Plant breeding

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vPLANT BREEDING
Plant Breeding: Art and Science
"Plant breeding means the improvement in the heredity of crops and production of new
crop varieties which are far better than original types in all aspects."
Smith (1966) defined plant breeding the following way: "Plant breeding is the art and science of
improving the genetic pattern of plants in relation to their economic use. Usually and ideally it involves
the effective cooperation with and help from the workers in somewhat remote disciplines”
Riley, 1978 defined plant breeding as a technology of developing superior crop plants/ varieties
for various purpose.
Frankel, 1958 defined plant breeding as the genetic adjustment of plants to the service man.
“Plant breeding is usually defined as the art and science for the improvement of crop plant science”. Its
objectives are to improve yield, quality, disease-resistance, drought and frost-tolerance and important
characteristics of the crops.
Objectives of Plant Breeding:
The prime aim of plant breeding is to improve the characteristics of plants that they become more
useful automatically and economically. Some of the objectives may be summarized as follows.
1. Higher Yield:Higher yield of grain, fodder, fibre, sugar, oil etc. developing hybrid varieties of Jawar,
Maize, Bajara, etc.
2. Improved Quality:The quality characters may vary from one crop to another such as grain size, shape,
colour, milling and backing quality of wheat, cooks quality in rice, malting in barley. Size shape and
flavour in fruits and keeping quality of vegetables, protein contents in legumes, methionine and
tryptophan contents in pulses etc.
3. Disease and Pest Resistance: Resistant varieties offer the cheapest and most convenient method of
disease and pest control. They not only helps to increase the production but also stabilize the productivity
E.g. Rust resistance in wheat.
4. Maturity Duration:aIt permits new crop rotation and extends crop area. Thus breeding for early
maturing varieties suitable for different dates of planting. This enables the farmer to take two-three crops
in a year.
5. Agronomic Characters:Three includes the characters such as dwarf, profuse tillering, branching erect
resistance and fertilizer responsiveness.
6. Photo and Thermo Insensitivity: Development of photo and thermo insensitive varieties in rice and
wheat will permit to extend their cultivation to new areas.
E.g Cultivation of wheat in Kerala and West Bengal, Cultivation of rice in Punjab and Himachal Pradesh.

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7. Synchronous Maturity: It is desirable in crops like mung ( Vigna radiate) where several pickings are
necessary.
8. Non-Shattering Characteristics: E.g. Mung, Black Gram, Horse Gram, etc.
9. Determinate Growth Habit: It is desirable in mung, pigeon pea and cotton, etc.
10. Dormancy: In some crops, seeds germinate even before harvesting if there are rains at the time of
maturity. E.g Mung, barley, etc. A period of dormancy in such cases would check the loss due to
germination while in other cases it may be removed it.
11. Varieties for a New Season: Breeding crops suitable for seasons.
E.g Maize (Kharif) which is grown in Rabi and summer also.
12. Moisture Stress and Salt Tolerance: Development of varieties for a rain fed area and saline soils
would help to increase crop production in India.
13. Elimination of Toxic Substance: It will help to make them safe for consumption E.g Khesari
( Lathyrus sativus) seeds have a neurotoxin causing paralysis.
14. Wider Adaptability: It helps in stabilizing the crop production over region and seasons.
15. Useful for Mechanical Cultivation: The variety developed should give response to application of
fertilizers, manures and irrigation, suitable for mechanical cultivation etc.

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PLANT INTRODUCTION
According to Allard (1960) plant introduction is the acquisition of superior varieties by importing
them from other areas. Or Plant introduction is the process of taking / introducing plants/ genotype or
group of genotype into new environment where they were not being grown before. Introduction may
involve new varieties of a crop already grown in the area wild relatives of the crop species or totally new
crop species for that area. Plant introduction may within the country between the countries or confirmed
between the states or within the state. The plant may be introduced from the country of another coninenet
.
“ The process of introducing plants from their native country to a new country”
Ex. Introduction of Ridley wheat varieties from Australia.
Introduction may be classified into two categories:
a) Primary b) Secondary
(1) Primary Introduction: -Introduction that can be used for commercial cultivation as a variety
without any change in the original genotype is referred to as primary introduction. There are several crops
in which direct use of introduced material has been successful. In wheat, varieties Sonora 64, Lerma
Rojo are examples of direct release of introduced material in India. These varieties were introduced from
Mexico and released directly for commercial cultivation in India. Similarly in semi-dwarf rice IR 8. IR 20
and IR 36 are examples of primary Introduction. Introductions that are immediately adapted to the
changed environment are known as direct introductions. Thus primary introduction can also be called as
direct introduction. Any foreign variety which is directly recommended for commercial cultivation in the
new environment (country) is called exotic variety.
(2) Secondary Introduction:- The introduced variety is subjected to selection, to isolate superior
variety or may be hybridized with local variety to transfer one or few desirable characters to the local
variety, known as secondary introduction. Secondary introduction is much more common than primary
introduction particularly in countries having well- organised crop improvement programme. Ex. Kalyan
sona and sonalika varieties selected from the material introduced from CIMMYT. Mexico (Centro
International de Mejoramieno de maize ‘Y’ Trigo) commonly known as Internation centre for maize and
wheat Research. . Thus secondary introduction can also be called as indirect introduction.
Procedure of Plant Introduction:
Plant introduction is one of the very old and effective methods of plant breeding. It consists of following
steps:
i) Procurement of Germplasm: Any individual or scientist or institute can introduce germplasm, but the
entire introduction must be routed through NBPGR, from the known source of the country or neighboring

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countries. While introducing germplasm scientist has to allow two routes. In case of the first route
individual make a direct request to individual or institution abroad and in the second route individual
submit his requirement to the NBPGR, by giving much detail information about the requirement.
Generally, the required materials are obtained through correspondence as gift, an exchange, purchased
etc. The plant part to be introduced depend upon the crop species, it may be seed, tubers, runners, suckers,
stolons, bulbs, Rhizome, cutting, bud or seedling. The part of the plant used for the propagation of a
species is known as propagule. The nature of propagules varies from species to species. Seeds general
have more viability than propagules and are packed and transported more easily, while propagules require
special packing techniques.
ii)Quarantine:-Quarantine means to keep the materials in isolation to prevent the spread of disease,
weeds etc. all the introduced material is thoroughly inspected for contamination with weed, disease and
insect pests. The material is fumigated or treated to avoid the contamination. If necessary, the materials
are grown in isolation for observation of disease, insect, pest and weeds, this entire process is known as
quarantine and the rules prescribed them are known as quarantine rules. All the materials being
introduced must be covered by an authentic phytosanitary certificate from the source of country i.e the
must be declared free from disease, weed and pests. If any country or material does not fulfill the
quarantine rules, that materials are likely to be destroyed by NBPGR or would return to the source
country.The quarantine controls is exercised by NBPGR at prescribed part of entry. E.g Mumbai, Calcatta
and Madras and this process is required at least three weeks.
III) Catloguing: -The introduced material is entered in accession register and is given on entry number.
The information regarding the name of the species, crop variety, and place of origin, adoption and
morphological character are reduced. The plant materials are classified into three groups viz.
a) Exotic Collection (EC)
b) Indigenous Collection (IC)
c) Indigenous Wild Collection (IW)
IV) Evaluation: -The introduced material is evaluated to assess the potential of new introduction and
their performance. These materials are evaluated at different substation. The material resistance to disease
and pest is evaluated under favourable environment conditions, and the promising one is either released
as such as a variety or subjected to selection or hybridization.
V) Multiplication and Distribution:-After evaluation promising material from production may be
increased by multiplication and released for general cultivation as varieties after necessary trials. Most of
there are identified for desirable character and maintain for future use.

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VI) Acclimatisation:-The process that leads to the adoption of a variety to a new environment is known
as acclimatisation. Generally the introduced varieties perform poorly because they are often not adapted
to the new environment. Sometimes the performances of that variety improve in the new environment by
growing it for number of generations. Acclimatisation is brought about by a faster growing it for number
of generations. Acclimatisation is brought about by a faster multiplication of those genotype that are
better adopted to new environment. The population having more variability is easily acclimatised i.e cross
pollinated crops is easily acclimatised than self pollinated crop.

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The Work of De Candolle
Alphonse de Candolle was a Swiss botanist. In 1883, he attempted to solve the mystery of the problems
of centres of origin of cultivated plants. He used historic writings, archaeological and ethnological
findings and linguistic writings to gather the information. Further, importance was given to areas
occupied by wild relatives of cultivated plants.
De Candolle concluded that cultivated plants had evolved from wild ancestors in restricted areas,
in the remote past. He pointed out , such centres - Old World and one centre in the New World. The
cultivated plants originated in these centres and spread to others areas.
The Old World Centres
The Old World refers to Europe, Asia and Africa. It has three centres of origin of cultivated
plants. They are china, south -West Asia and Egypt. Based on the time of domestication, De Candolle
classified the cultivated plants into three groups. They are mentioned below .
1. Plants Cultivated for at least 4000 Years
All plants cultivated before 2115 BC are included in this group,
Eg:,
Ahnond fig Rice
Apple Grape Sorghum
Banana Hemp Soya bean
Barley Mango Tea
Cabbage Onion Wheat
Date
All plants domesticated in between 2115 8C and 115 BC are included in this group. Examples-
Alfaalfa Oats Pepper Walnut
Asparagus Carrot Citrus
Mustard Pea Sugarcane
3. Plants Cultivated for Less than 2000 years
All plants domesticated after 115 BC are included in this group,
Examples-
Cofee Raspberry
Muskmelon Strawberry
The New World Centres
The New World represents the North Amenica and the South America. It has only one centre of the
origin of cultivated plants. it occupies interetropical America. Based on the time of domestication, the
cultivated plants are grouped into three categories. They are mentioned below

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All plants domesticated before 115 BC are included in this group,
Cacao Sweet potato
Maize Tobacco
2. Plants Domesticated Before the Time of Columbus
All plants domesticated before 1498 AD are included in this group. Examples-
Cotton Pineapple
Guava Potato
Groundnut Pumpkin
Tomato
3. Plants Domesticated Since the Time of Columbus
All plants domesticated after 1498 AD included in this group. Examples-
Black walnut Plum
Chinchona Rubber
De Candolle concluded that each cultivated plant has a single Centre of domestication. However,
he failed to explain the wild, ancestors and the changes of the ancestors during the repeated cultivations.
This is the drawback of De Candolle's system.
The Work of Vavilov
Nikolai Ivanovich Vavilov (1926, 1951), a Russian geneticist and plant breeder, was the pioneer
man who realized the significance of genetic diversity for crop improvement. Vavilov and his colleagues
visited several countries and collected cultivated plants and their wild relatives for use in the Russian
breeding programme to develop varieties for various agro climatic conditions of USSR. Based on his
studies of global exploration and collection, Vavilov proposed eight main centres of diversity and three
subsidiary centres of diversity given as follows
1. Main centres- Main centres of crop diversity as proposed by Vavilov are (1) China, (2) India
(Hindustan), (3) Central Asia, (4) Asia Minor or Persia, (5) Mediterranean, (6) Abyssinia, (7)
Central America or Mexico, and (8) South America.
2. Subsidiary Centers - There are three subsidiary centres of diversity. These are: (1) Indo-Malaya, (2)
Chile, and (3) Brazil and Paraguay. All these centres are known as centres of origin or centres

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of diversity or Vavilovian centres of diversity. Vavilovian centres of diversity of crop plants
–– Main crops for which genetic diversity is found
A)Main centres
I. China Naked oat (SC), Soybean, Adzuki bean, Common bean (SC), Small Bamboo,
Leaf Mustard (SC), Peach, Orai Sesame (SC), China tea, etc.
2. Hindustan Rice, Chickpea, Moth Bean, Rice bean, Horsegram, Brinjal, Cucumber, Tree
Cotton,Jute, Pepper, African Millet, Indigo, etc.
3. Central Asia Bread wheat, Club wheat, Shot wheat, Rye (SC), Pea, Lentil, Chickpea,
Sesame, Flax,Safflower, Carrot, Radish, Apple, Pear and Walnut.
4, Asia Minor or Persia Einkorn wheat, Durum wheat, Poulard wheat, Bread wheat, Two Rowed
barley, Rye, Red oat, Chickpea (SC) lentil, Pea (SC), Flax, Almond,
Pomegranate, Pistachio, Apricot and Grape.
5. Mediterranean Durum wheat, Husked oats, Olive, Broad bean and Lettuce
6. Abyssinia Durum wheat, Poulard wheat. Emmer wheat, Barley, Chickpea, Lentil, Pea,
Flax. Sesame, Castor bean, African Millet, and coffee.
7. Central America or
Mexico
Maize, Common bean, Upland cotton, Pumpkin Gourd, Squash, Sisal hemp
and Pepper.
8. South America Potato Sweet potato, Lima bean, Tobacco and Sea Island cotton
B.Subsidiary entres
9. Indo-Malaysia Banana, Coconut, Yam, and Pomelo
10. Chile Potato
11. Brazil and Paraguay Peanut, Rubber, Cocoa, Pineapple.
Kinds Of Germplasm

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The sum total of all the hereditary material is referred as germplasm. In other words, gene pool refers to a
whole library of different alleles of a species Germplasm or gene pool is the basic material with which a
plant breeder has to initiate his breeding programme.
A. Land races
Land races are nothing but primitive cultivar which were selected and cultivated by the farmers for many
generations.
Land races have high level of genetic diversity which provides them high degree of resistance to biotic
and a biotic stresses. Biotic stress refers to hazards of diseases and insects, whereas a biotic stress means,
drought, salinity, cold, frost, etc.
Land races have broad genetic base which again provides them wider adaptability and protection from
epidemic of diseases and insects.
B. Obsolete Cultivars
Improved varieties of recent past are known as obsolete cultivars. These are the varieties which were
popular earlier and now have been replaced by new varieties.
For example, varieties K68, K65 and Pb 591 were most popular traditional tall varieties
before introduction of high yielding dwarf Mexican wheat varieties.
C. Modern Cultivars
The currently cultivated high yielding varieties are referred to as modern cultivars. These varieties have
high yield potential and uniformity as compared to obsolete varieties and land races.
Modem cultivars constitute a major part of working collections and are extensively used as parents in the
breeding programme.
D.Advanced Breeding lines
Pre-released plants which have been developed by plant breeders for use in modem scientific plant
breeding are known as advanced lines, cultures and stocks.
E.Wild forms of Cultivated Species
Wild forms of cultivated species are available in crop plants. Such plants have generally high degree of
resistance to biotic and a biotic stresses and are utilized in breeding programmes for genetic improvement
of resistance to biotic and a biotic stresses.
F. Wild Relatives Those naturally occurring plant species which have common ancestry with crops and
can cross with crop species are referred to as wild relatives or wild species.
Wild relatives are important sources of resistance to biotic (diseases and insects) and a biotic (drought,
cold, frost, salinity, etc.) stresses.
G. Mutants

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Mutation breeding is used when the desired character is not found in the genetic stocks of cultivated
species and their wild relatives. Mutations do occur in nature as well as can be induced through the use of
physical and chemical mutagens.
For example, mutant genepool Dee-Geo-Woo-Gen in rice and Norin 10 in wheat proved to be valuable
genetic resources in the development of high yielding and semi dwarf varieties in the respective crop
species.
Types of Centres of Diversity of Crops
The centres of crop diversity of three types viz:
1) Primary centres of diversity,
2) Secondary centres of diversity
3) Micro –Centres.
1. Primary Centres of Diversity:
Primary centres are regions of vast genetic diversity of crop plants. These are original homes of the crop
plants which are generally uncultivated areas like, mountains , hills, river valleys, forests, etc. Main
features of these centres are given below:
1. They have wide genetic diversity.
2. Have large number of dominant genes.
3. Mostly have wild characters.
4. Exhibit less crossing over.
5. Natural selection operates.
2. Secondary Centres of Diversity:
Vavilov suggested that values forms of crop plants are found for away from their primary area of
origin, which he called secondary centres of origin or diversity. These are generally the cultivated areas
and have following main features.
1. Have lesser genetic diversity than primary centres.
2. Have large number of recessive genes.
3. Mostly have desirable characters.
4. Exhibit more crossing over
5. Both natural and artificial selections operate.
3. Microcenters:
In some case, small areas within the centres of diversity exhibit tremendous genetic diversity of some
crop plants. These areas are referred to as micro-centres. Microcenter is important sources for collecting
valuable plant forms and also for the study of evolution of cultivated species. The main features of micro
centres are given below:
1. They represent small areas within the centres of diversity.
2. Exhibit tremendous genetic diversity.
3. The rate of natural evolution is faster than larger areas.
4. They are important sites for the study of crop evolution.

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Germplasm Activity – Conservation
Conservation refers to protection of genetic diversity of crop plants from genetic erosion. There
are two important methods of germplasm conservation or preservation viz.
1)In situ conservation, 2) Ex situ conservation.
1) In-situ Conservation: -Conservation of germplasm under natural habitat is referred to as in situ
conservation. It requires establishment of natural or biosphere reserved national parks or protection of
endangered areas or species. In this method of conservation, the wild species and the complete natural or
semi natural ecosystem are preserved together. This method of preservation has following main
disadvantages.
1. Each protected are will cover only very small portion of total diversity of a crop species, hence several
areas will have to be conserved for a single species.
2. The management of such areas also poses several problems.
3. This is a costly method of germplasm conservation.
2) Ex-Situ Conservation:
It refers to preservation of germplasm s. This is the most practical method of germplasm conservation.
This method has following three advantages:
1. It is possible to preserve entire genetic diversity of a crop species at one place.
2. Handling of germplasm is also easy.
3. This is a cheap method of germplasm conservation.
The germplasm is conserved either 1) In the form of seed. Or 2) In the form of meristem cultures.
Preservation in the form of seed is most common and easy method. Seed conservation is relatively safe,
requires minimum space (except coconut, etc) and easy to maintain .Glass, tin or plastic containers are
used for preservation and storage of seeds. The seeds can be conserved under long term (50 to 100 years),
medium term (10-15 years) and short term ( 3-5 years) storage condition. Roberts (1973) has classified
seeds into two groups for storage purpose, viz. 1) orthodox and 2) Recalcitrant.
1. Orthodox:
Seeds which can be dried to low moisture content and stored at low temperature without losing
their viability are known as orthodox seeds. This group includes seeds of corn, wheat, rice, carrot, beets,
papaya, pepper, chickpea, lentil, soybean, cotton, sunflower, various beans, egg plant and all the
Brassicas. These seeds can be dried and stored at low temperatures for long periods of time.
2. Recalcitrant:
Seeds which show very drastic loss in viability with a degree in moisture content below 12 to 13%
are known as recalcitrant seeds. This group includes cocoa, coconut, mango, tea, coffee, and rubber,
jackfruit, and oil palm seeds. Such seeds cannot be conserved in seed banks and therefore, require in situ
conservation. Crop species with recalcitrant seeds are conserved in field gene banks which are simply
areas of land in which collections of growing plants are assembled.

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For conservation of meristem cultures, meristem cultures, meristem or shoot tip banks are established.
Conservation of genetic stocks by meristem cultures has several advantages as given below:
1. Exact genotype can be conserved indefinitely free from virus or other pathogens and without loss of
genetic integrity.
2. It is advantages for vegetatively propagated crops like potato, sweet potato, cassava, etc, because seed
production in these crops is poor.
3. Vegetatively propagated material can be saved from natural disasters or pathogen attack.
4. Long regeneration cycle can be envisaged from meristem cultures.
5. Perennial plants which take 10-20 years to produce seeds can be preserved any time by meristem
cultures.
6. Regeneration of meristem is extremely easy.
7. Plant species having recalcitrant seeds can be easily conserved by meristem cultures.
Germplasm Activity – Utilization
Utilization refers to use of germplasm in crop improvement programmes. The germplasm can be
utilized in various ways. The uses of cultivated and wild species of germplasm are briefly discussed
below:
Cultivated Germplasm:
The cultivated germplasm can be used in three main ways:
1) As a variety,
2) as a parent in the hybridization, and
3) as a variant in the gene pool.
Some germplasm lines can be released directly as varieties after testing. If the performance of an
exotic line is better than a local variety, it can be released for commercial cultivation. In some cases, new
variety is developed through selection from the collection. Some germplasm lines are not useful as such,
but have some special characters, such as disease resistance, good quality of economic produce, or wider
adaptability. These characters can be transferred to commercial cultivars by incorporating such
germplasm lines in the hybridization programmes. Transfer of desirable character from cultivated
germplasm to the commercial cultivars is very easy because of cross compatibility.
Wild Germplasm:
The wild germplasm is used to transfer resistance to biotic and abiotic stresses, wider adaptability and
sometimes quality such as fibre strength in cotton. However, utilization of wild germplasm poses three
main problems: viz 1) Hybrid inviability- inability of a hybrid to survive, 2) Hybrid sterility – Inability of

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a hybrid to produce offspring, and 3) Linkage of undesirable characters with desirable ones. Thus
utilization of wild germplasm for crop improvement is a difficult task.
Gene Banks
Gene bank refers to a place or organization where germplasm can be conserved in living state. Gene
banks are also known as germplasm banks. The germplasm is stored in the form of seeds, pollen or in
vitro cultures, or in the case of a field gene bank, as plants growing in the field. Gene banks are mainly of
two types,
(1) Seedgene banks (2) Field gene banks
1. SeedGene bank
A place where germplasm is conserved in the form of seeds is called seed gene bank. Seeds are very
convenient for storage because they occupy smaller space than whole plants. However, seeds of all crops
can not be stored at low temperature in the seed banks. The germplasm of only orthodox species (whose
seed can be dried to low moisture content without losing variability) can be conserved in seed banks. In
the seed banks, there are three types of conservation, viz.,
(1) Short term (2) Medium term (3) Long-term.
Base collections are conserved for long term (50 years or more) at -18 or -20°C.
Active collections are stored for medium term (10-15 years) at zero degrees Celsius.
Working collectionis stored for short term (3-5 years) at 5-10°C.
Advantages of gene banks
1. Large number of germplasm samples or entire variability can be conserved in a very small space.
2. In seed banks, handling of germplasm is easy.
3. Germplasm is conserved under pathogen and insect free environment.
Disadvantages
1. Seeds of recalcitrant species can not be stored in seed banks.
2. Failure of power supply may lead to loss of viability and thereby loss of germplasm.
3. It requires periodical evaluation of seed viability. After some time multiplication is essential to get new
or fresh seeds for storage.
2. Field Gene banks
Field gene banks also called plant gene banks are areas of land in which germplasm collections of
growing plants are assembled. This is also called ex-situ conservation of germplasm. Those plant
species that have recalcitrant seeds or do not produce seeds readily are conserved in field gene banks. In
field gene banks, germplasm is maintained in the form of plants as a permanent living collection. Field

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gene banks are often established to maintain working collections of living plants for experimental
purposes. They are used as source of germplasm for species such as coconut, rubber, mango, cassava,
yam and cocoa. Field gene banks have been established in many countries for different crops.
Established field gene banks
Name of country Crop species for which field gene bank is established
Malaysia Oil palm has been conserved on 500 ha.
Indonesia Marked 1000 ha. Area for coconut and other perennial crops.
Philippines South East Asian germplasm of banana has been conserved.
India Global collection of coconut has been conserved to Andman and Nicobar.
Advantages
1. It provides opportunities for continuous evaluation for various economic characters.
2. It can be directly utilized in the breeding programme.
Disadvantages
1. Field gene banks can not cover the entire genetic diversity of a species. It can cover only a fraction of
the full range of diversity of a species.
2. The germplasm in field gene banks is exposed to pathogens and insects and sometimes is damaged by
natural disasters such as bushfires, cyclones, floods, etc.
3. Maintenance of germplasm in the field gene banks is costly.
NBPGR:
National Bureau of Plant Genetic Resources was established by Indian Council of Agricultural
Research (ICAR) in 1976 in New Delhi. In India, introduction started in 1946 at IARI. New Delhi in the
division of Botany. In 1961 a separate division of Plant Introduction was established under the leadership
of Dr. H.B. Singh who made remarkable contribution in the field of plant Introduction in India. He made
huge collections of germplasm of various crop species and systematized the work. In 1976, the division
of plant Introduction was elevated to the status of independent agency known as NBPGR.
The basis function of NBPGR is to conduct research and promote collection, conservation, evaluation,
documentation and utilization of crop genetic resources in India. NBPGR is assigned by various crop
research institutes in the collection, conservation, evaluation and documentation of crop genetic
resources. The main function of NBPGR is briefly presented below:
Functions:

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1. NBPGR is the sole agency in India for Import and export of plant genetic resources. Thus it helps in
exchange of germplasm.
2. It promotes, national genetic resources activities, viz collection, conservation, evaluation,
documentation and utilization of crop plants, and coordinates in all these activities.
3. NBPGR has five stations which are located at 1) Shimla, Himachal Pradesh, 2) Jodhpur, Rajasthan,
3) Akola, Maharashtra, 4) Kanya Kumari, Kerala, and 5) Shillong, Meghalaya. Collections of
various crops are evaluated by these centres.
4. NBPGR also organise short term training courses on collection, conservation, evaluation,
documentation, and utilization of crop genetic resources.
5. National and International exploration and collection trips are also organised by NBPGR, National
collection trips are organised in collaboration with the help concerned Crop Research Institutes and
International trips are arranged with the help of IPGR/FAO.
6. NBPGR provides guidance about development of cold storage facilities for medium and short term
conservation of germplasm.
7. NBPGR also takes decision about setting up of gene sanctuaries for endangered crop species.
SELECTION
One of the oldest method of breeding and is the basis for all crop improvement, practised by
farmer in ancient times. Selection is essentially based on the phenotype of plants. Consequently the
effectiveness of selection primarily depends upon the degree to which the phenotypes of plants reflect
their genotype.
Selection may be natural or artificial by which individual or group of plants are isolated from a mixed
population. Before domestication, crop species were subjected for natural selection. Natural selection is
the rule and has resulted in evolution of several local varieties of crop. After domestication man has
knowingly or unknowingly practiced some selection known as the artificial selection. For a long period
under domestication natural selection was perhaps the more selection is a little value and current breeding
method entirely depends on artificial selection.
Selection has two basic characteristics or limitation
i)Selectionis effective for heritable differences.
ii) Selection does not create variation, it only utilize the variation already present in the population. Thus

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the two basic requirement of selection are a) Variation must be present in the population and b) Variation
must be heritable.
Methods of selection
i) Pure Line Selection ii) Mass Selection. iii) Clonal selection
Pure Line Selection
The concept of pure line was proposed by Danish botanist Johannsen in 1903 on the basis of his
studies on Princess beans (Phaseolus vulgaris) , which is highly self pollinated species. He obtained
commercial seed lot of princess variety of bean. The commercial seed lot showed variation for seed size.
He selected large and small seeds and grew them separately. The progenies thus obtained differed in seed
size. The progenies of larger seeds are generally larger than those obtained from smaller seeds. This
clearly showed that the variation in seed size in the commercial seed lot of princess’s variety of French
bean had genetic basis, due to which selection for seed size was effective.
Johanssen further studied and established 19 pure line, each line was a progeny of a single seed
from the original seed lot. Within each pure line has again selected large and small seeds. The progenies
of the large and small seeds from a single pure line varied in weight of individual seed, but the average
weight of progeny from larger seed was quite similar to the average weight of progeny from the small
seed within the same pure line.
He concludes that the population of self-fertilized species consists of several homozygous
genotypes. Variation in such a population has genetic base and therefore, selection is effective. The
progenies of single self fertilized homozygous plants having identical genotypes Pure Lines and the
variation within pure lines is purely environment and thus selection within pure lines is ineffective.
Pure Line Selection:
In pure line selection, large numbers of plants are selected from a self-pollinated crop and is
harvested individually, individual plant progenies from them are evaluated separately and the best one is
released as pure line variety. Therefore it is also known as individual plant selection.
Characteristics of Pure Line :
1. All plant within a pure line has same genotype as the plants from which the pure lines are derived.
2. The phenotypic differences (variation) within a pure line is environmental and therefore non heritable.
3. The pure line becomes genetically variable with time, due to mechanical mixture, mutation, etc.
Uses of Pure Line:
1. Superior line is used as variety.
2. It is used as parent in development of new variety by hybridization.
3. Pure lines are used for studying mutations and other biological investigations such as medicine,
immunology, physiology, and biochemistry.

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IQC ASL
Procedure of Pure Line Selection:
The pure line selectionhas three steps.
1. Selection of individual plants from a local variety or from mixed population.
2. Visual evaluation of individual plant progenies.
3. Yield Trials.
First Year:
Select large number of plants (200-3000) from local variety or some other mixed population and their
seeds are harvested separately. In case of individual plants can’t be identified individual heads may be
selected on the basis of easily observable characters, such as flowering, maturity duration disease,
resistance, presence of awns , plant height etc. It is advisable to select plants for easily observable
characteristics.
Second Year:
Selected individual plants progenies are grown with proper spacing weak along with standard variety
row. Progenies are evaluated visually and poor weak and defective segregating progenies are rejected on
the basis of visual characteristics. The member of progenies selected should be less to facilitate replicated
yield trials if necessary this process may be repeated for one or more years.
Third Year:
Grow the selected progenies in a replicated trails for critical evaluation. The best variety is used as
a check for comparison and planted after every 20-25 progenies. If sufficient seeds are available,
preliminary yield trial may be conducted. Selection is made for easily observable, preliminary yield trial
may be conducted. Selection is made for easily observable characters including disease resistance and
numbers of progenies are reduced.
Fourth to Seventh Year:
Replicated main yield trails are conduced using best variety as a check quality test is also conducted and
used as a basis of selection. Each progeny is an experimental stain as it is pure line. The promising strains
are evaluated at several locations along with other strains in cordianted yield trials. The most promising
strains are identified.
Eight Year:
The best progeny is released as a new variety and its seed is multiplied for distribution to farmers.
Merits of Pure Line Selection Method:
1. Pure line selection achieves maximum possible improvement over the original variety.
2. Being extremely uniform, more liked by farmers and consumers than those developed by other
methods like mass selection.
3. It is easier than hybridization required less skill.

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IQC ASL
4. Used for developing inbred lines and pure lines.
5. Due to extreme uniformly, it is easily indentified in seed certification.
Demerits of Pure Line Selection Method:
1. It is not practiced in cross pollinated crops because it is expensive, laborious.
2. The variety developed can’t be easily maintained by the farmers.
3. The varieties developed by pure line selection don’t have wide adaptability and stability in production.
4. The upper limit on the improvement is created by the genetic variation present in the original
population.
5. It requires more time and laborious than mass selection.
6. The breeder’s has to devote more time to pure line selection than mass selection.
Applications of Pure Line Selection:
1. It is used for improvement of local varieties, have a considerable genetic variability, e.g Wheat var.NP-
4 and NP-52.
2. It is practised in introduced material to develop suitable varieties e.g shining mung -1 selected from
Kulu type-1, Kalyan sona from CIMMYT.
3. It is used for improvement of old pure line varieties, e.g Chafa, from No.816 (gram) , Jalgaon 781 from
China Mung 781.
4. It provides an opportunity for selection of new characteristics, such as disease resistance, grain type ,
plant type, etc.
5. It provides an opportunity for selection in the segregating generation from crosses.
Achievements:
A large number of improved varieties have been developed in self pollinated crop like wheat, barley, rice,
pulses, and oilseeds, cotton and many vegetables etc. Many wheat varieties developed include NP-4, NP-
6, NP-12, NP-28, Mung Var, T-1, B-1, tobacco chatham special-9, etc.
Mass Selection:
Mass selection is a simplest , common and oldest method of crop improvement, in which large
number of plants of similar phenotype are selected and their seeds are harvested and mixed together to
constitute the new variety. This method is practised in both self and cross – pollinated crops and plants
are selected on the basis of their phenotype of appearance. Therefore, selection is done for easily
observable characteristics such as plant height, ear/type, grain colour, grain size, etc.
The original population would have been a mixture of several pure lines and the plants selected from it
would be homozygous. But the variety developed through mass selection would have a considerable
genetic variation and consequently, further mass selection or pure line selection may be done in such a
variety. Generally, the plants selected in mass selection are not subjected to progeny test.
There are two methods of mass selection.

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IQC ASL
1) Hallets Method (1869):
In this method the crop is grown under the best environmental conditions and maximum amounts of
water and fertilization to given and then mass selection practised.
2) Rimpar Method (1867):
In this method the crop is grown under ordinary condition or unfavourable conditions with minimum
water and fertilizers and the mass selection is practised. It is more effective and easily applicable.
Application of Mass Selection:
In self pollinated crops, mass selection has two major applications. i.e
i) Improvement of local varieties
ii) Purification of existing pure line varieties.
i) Improvement of Local or Deshi Varieties:
The local varieties are mixtures of several genotypes, which may differ in flowering or maturity plant
height, disease resistant etc. Many of these plants type would be inferior and low yielding, such plants
will be eliminated through mass selection and local variety would be improved without adversely
affecting its adaptability and stability. Because the new variety would be made up of the most of the
superior plants type present in the original local variety.
ii) Purification of Existing Pure Line Varieties:
Pure lines tend to become variable with time due to mechanical mixtures, natural hybridization,
mutation etc. therefore, it is necessary that the purity of pure line varieties be maintained through regular
mass selection. Mass selection is generally important and practised in cross-pollinated crop and has the
only limited application in self pollinated crop.
Procedure of Mass Selection:
First Year:
A large number of phenotypically similar plants are selected at the time of harvest on the basis of their
vigour, plant type, disease resistance and other desirable characteristics. Few hundred to several thousand
plants are selected. The unit of selection may be plant, head of seed. The selected plants are harvested and
seed mixed together to grow next generation. Selection of too more plants should be avoided in the first
year.
Second Year:
The composite seed is planted in a preliminary yield trial along with standard variety as a check. If this
method is used for purification of old mixed variety from which the selection was made, should also be
included as a check. Observe the phenotypic characters critically. The best performances are retained and
others are discarded.

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IQC ASL
Third to Sixth Year:
The superior strains are evaluated for their performance in co-ordinated yield trails at several locations,
first in an initial evaluation trail (IET) for one year, if found promising promoted to uniform variety trail
(UVT) for two or more years. Only promising one is identified for release as new variety.
Seventh Year:
Promising strain may be released for cultivation by multiplication and distribution to the farmer for
general cultivation. If recommended by central variety release committee.
Advantages of Mass Selection:
1. Since large numbers of plants are selected, the variety developed through mass selection is more
widely adapted than pure lines.
2. It is easiest , simplest and quickest method of plant breeding because there is no controlled pollination,
no progeny testing and prolonged yield trials as well as it is more of an than a science.
3. Mass selection retains considerable genetic variability and hence variety can be improved after few
years by another mass selection.
4. The breeder can developed more time to another programme as it is less demanding method.
5. Used for improving wind local variations to meet the immediate need of the farmers.
Disadvantages of Mass Selection:
1. The varieties developed by this method show variation and are not uniform as pure lines hence less
preferred by the farmers than pure lines.
2. In the absence of progeny test, it is not possible to determine whether the selected plats are
homozygous for specific characters. Similarly, whether phenotypic superiority of selected plants is due to
environment of the genotype can’t be determined.
3. The varieties developed by mass selection are more difficult to identify than pure lines in seed
certification programme.
4. It utilizes the variability already present, in the population hence, it can’t generate new genetic
variability.
5. It is not useful for improvement in quantitative characters, such as yield because phenotypic and
environmental effects can’t be separated out.
6. Improvement is short lived, since the variety produced is a mixture of different genotypes, hence,
required to be repeated every year in cross-pollinated crops.
Breeding Procedures of Clonal Selection
The procedure of selection used for asexually propagated crops is known as clonal selection,
since the selected plants are used to produce new clones. Or Improvement of asexually propagated crop
y selecting superior clones is known as clonal selection. Superior clones can be isolated from three types
of materials viz. 1) Local variety, 2) Introduced variety, and 3) Inter crossed populations.

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IQC ASL
The phenotypic value of a plant or clone is due to the effects of its genotype (G) , the environment (E)
and the genotype X environment ( G X E) interaction of these only the genotypic ( G) effects are heritable
and therefore stable. The environment and interaction effects are non- heritable and cannot be selected
for. Therefore, selection for quantitative characters based on the observation on single plants is highly
unreliable. In view of this consideration , in the earlier stage of clonal selection , when selection is based
on single plant or single plots the emphasis is given on elimination of weak and undesirable plants or
clones.
The Various Steps Involved in Clonal Selection:
1. First Year: From a mixed variable population few hundred to few thousand desirable plants are
selected. A rigid selection can be done for simply inherited characters with high heritability. Plants with
obvious weaknesses are eliminated.
2. Second Year: Clones from the selected plants are grown separately, without replication. This is done
in view of the limited supply of propagating material for each clone and because of the large number of
clones involved. The number of clones is drastically reduced, and inferior clones are eliminated. The
selection is based on visual observation. Finally, fifty to one hundred clones may be selected on the basis
of clonal characteristics.
3. Third Year:
A replicated preliminary yield trial is conducted by using suitable check for comparison. Few superior
performing clones with desirable characteristics are selected for multi location trails.
4. Fourth to Sixth Years:
A replicated yield trail is conducted at several locations along with a suitable check. The best clone that is
superior to the check in one or more characteristics is identified for release as a new variety.
5. Seventh Year:
The superior clone is multiplied and released as a new variety.

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IQC ASL
HYBRIDIZATION
Hybridization is one of the methods for developing new variety by crossing two lines or plants having
unlike genetic constitution or it is the mating or crossing of two plants or lines of dissimilar genotype
inorder to combine desirable characters from both the parents.
One of the objectives of hybridization is to create genetic variation. Two genotypically different plants
are crossed together to obtain F1 generation. F1 is advanced to generate F2generation. The degree of
genetic variation in F2 and subsequent generation depend on number of heterozygous genes in F1.
Procedure of developing hybrid variety
The breeder has clear cut objective in developing the variety. He has to select the variety accordingly.
1. Choice of parents: One of the parent involved in crosses should be a well adapted and proven variety
in the area. The other variety should be having the character that are absent in this variety. Combining
ability of the parents serves as useful guides in the selection of parents, which produce superior F1 and
F2.
2. Evaluation of parents: Parents are evaluated for their combining ability.
3. Emasculation: The removal of stamens/anther without affecting the female reproductive organs, hand
emasculation is mostly followed.
(If flowers are large enough to do manual emasculation, forceps or scissor method is adopted for
emasculation. Egs. Padt, Wheat, cotton, etc. The base of flower is held between thumb and index finger
of the left hand. With the right hand, the flower bud is opened using forceps and then stamens are pulled
out with the forceps or scissors. This is a tedious and painstaking work in hybridization.. ·
In plants with very small-sized flowers, emasculation is done by using hot water method. Eg. Sorghum,
barley etc. The panicle is kept dipped in hot water (45-53oC) in a jug for 1-10 minutes. The hot water
inacavates the stamen to avoid sepollination.
In some crops, male sterility is introduced into plants either by back cross method or by treatment with 2,
4-D or NAA or maleic hydroxide during the growth stage. Then the male sterile plant is used as a female
parent. Here. There is no need for emasculation. This method is often called male sterility method.)
4. Bagging: Immediately after emasculation the flowers are enclosed in suitable bags to prevent cross
pollination.
5. Tagging: The emasculated flowers are tied with a thread. The information on date of emasculation,
date of pollination, name of female and male parents are recorded in the tag with pencil. The name of the
female parent is written first then male parent.
6. Pollination: Mature fertile and viable pollen from the male parent should be placed on receptive stigma
of emasculated flowers to bring about fertilization. Pollen grain is collected, allowed for dehiscence and
pollination is carried out with camel hair brush.

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IQC ASL
7. Harvesting and storing of F1 seeds: The crossed heads/pods should be harvested and threshed. The
seeds should be dried and properly stored to protect them from storage pests.
8. Rising the F1 generation: Identify the selfed seeds in the F1generation by using dominant marker gene.
Larger F1 population is desirable, because both the genes are present in heterozygous condition.
9. Selfing: To avoid cross pollination andto ensureself pollination. In often cross pollinated crops they are
bagged to prevent cross pollination.
Pedigree method
In pedigree method individual plants are selected from F2 and their progenies are tested in subsequent
generations. A record of the entire parent off spring relationship is maintained and known as pedigree
record. The pedigree may be defined as a description of the ancestor of an individual and it generally goes
back to some distant ancestor. So each progeny in every generation can be traced back to the F2 plant
from which it is originated.
Procedure:
1. Hybridization: The selected parents are crossed to produce a simple / complex cross(F1 seed)
2. F1generation: F1 seeds are space planted to each produces maximum number of F2 seed. 15-30
F1plants are sufficient to produce good F2 populations.
3. F2generation: 200-10000 plants are space planted and 100-500 plants are selected and their seeds are
harvested separately. He should select as many as F2 plants as he can handle efficiently.
The selection depends on skill of the breeder and his ability to judge to select F2 which produce good
progeny.
4. F3 Generation: Individual plant progeny are space planted. Individual plant with desirable characters
from superior progenies is selected.
5. F4 Generation: Individual plants progenies are space planted desirable pants are selected undesirable
progenies are rejected. Progenies are compared visually and more plants are selected from superior
progenies. Selection of desirable plants from superior progenies selection is practiced within / between
family.

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IQC ASL
6. F5Generation: Many families have
reached homozygous and may be
harvested in bulk. The breeder has to
assess the yielding potential of progenies,
25-100 progenies are advanced and tested
inpreliminary yield trial.
7. F6 Generation: Multi row plots and
evaluated visually progenies harvested
bulk and they have become homozygous.
8. F7 Generation: Preliminary yield
trail with replication to identify the
superior progenies. Progenies are
evaluated for other component
character 2-5 outstanding lines
superior to check are advanced to
multi location testing.
9. F8 –F10 Generation: Replicated
yield trial at several locations. They
are tested for yield as well as for
resistance.
10. F11: Seed multiplication and release.

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IQC ASL
Bulk method
Bulk method was first used by Nilsson Ehlein 1908. F2 and the subsequent generation are harvested as
bulks to raise the next generation. At the end of bulking period individual plants are selected and
evaluated in a similar manner as in the pedigree method.The duration of bulking may vary from 7-30
generation artificial selection may seldom be practiced
Procedure for Bulk method
1. Hybridization: Parents are selected and crossed
2. F1 generation : F1is space planted more than 200 F1 plants
3. F2-F6 Generation: Planted at commercial seed rate, spacing and harvested as bulk, during this period.
Frequency of population changes due to out break of disease or pest.
4. Artificial selection is done, largepopulation is raised,30000-50000 plants in each generation.
5. F7 generation: 50000 plants are space planted about 1000-5000 plants with phenotype is selected and
the seeds are harvested separately.
6. F8 generation: Individual plant progenies are single/multi row plants, since progenies are homogygous
and harvested in bulk weak and inferior progenies are rejected and 100-300 individual plant progenies
with desirable characters.
7. F9 Generation: Preliminary yield trial with standard check, yield and quality parameter is taken
for selection.
8. F10---F12 generation: Replicated yield trails are conducted. Yield and its component characters are
evaluated along with the check. Superior progenies are released as variet
9. F13 generation: Seed multiplication of the newly released variety and distribution to farmers.

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IQC ASL
DISTANT HYBRIDIZATION
Distant hybridization Hybridization between individuals from different species
belonging the same genus (interspecific hybridization) or two different genera of same
family (intergeneric hybridization) is termed as distant hybridization and such crosses are
known as distant crosses or wide crosses
Main features of Interspecific or Intergeneric hybridization
1. It is used when the desirable character is not found within the species of a crop.
2. It is an effective method of transferring desirable gene into cultivated plants from their related
cultivated or wild species.
3. It is more successful in vegetatively propagated species like sugarcane and potato than in seed
propagated species.
4. It gives rise to three types of crosses viz. a) fully fertile, b) Partially fertile and c) Fully sterile in
different crop species.
5. It leads to introgression which refer to transfer of some genes from one species into genome of another
species
Ex. Sugarcane varieties have been developed by crossing Saccharum oficinarum X Saccharum
barberi, while in cotton G.arboreum X G. hirsutum. When two different species belongs to different
genera known as Intergeneric hybridization. Ex. Triticale is developed by crossing Triticum aestivum
X secale cereal (Rye). Generally the objectives of such crosses are to transfer one or few characters,
like disease resistance.
Male Sterility
Male sterility is defined as an absence or non-function of pollen grain in plant or incapability of
plants to produce or release functional pollen grains. The use of male sterility in hybrid seed production
has a great importance as it eliminate the process of mechanical emasculation.
Types of Male Sterility:
The male sterility is of five types 1) Genetic male sterility, 2) Cytoplasmic male sterility, 3) Cytoplasmic
genetic male sterility, 4) Chemical induced male sterility and 5) Transgenic male sterility.
1) Genetic Male Sterility:
The pollen sterility, which is caused by nuclear genes, is termed as genic or genetic male sterility.
It is usually governed by a single recessive gene ms or ‘s’ with monogenic inheritance, but dominant gene
governing male sterility are also known E.g Safflower. The male sterility alleles may rise spontaneously
or it can be induced artificially and is found in several crops viz. Pigeon pea, castor, tomato, limabean,
barley, cotton, etc. A male sterile line may be maintained by crossing it with heterozygous male fertile
plant, such a mating produces 1:1 male sterile and male fertile plants.
Utilization in Plant Breeding:
Genetic male sterility is usually recessive and monogenic hence can be used in hybrid seed production. It
is used in both seed propagated crops and vegetatively propagated species. In this progeny from crosses (

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IQC ASL
msms X Msms) are used as a female and are inter planted with homozygous male fertile ( MsMs)
pollinator. The genotypes of msms and Msms lines are identical except for the ‘ms’ locus i.e. they are
isogenic and are known as male sterile A) Maintainer B) Line respectively. The female line
would . Therefore contain both male sterile and male fertile and male fertile plants, the later must be
identified and removed before pollen shedding. This is done by identifying the male fertile plants in
seeding stage either due to the pleiotrophic effect of ms gene or due to phenotypic effect of closely lined
genes. In this rouguing of male fertile plant from the female is costly operation and due to this cost of
hybrid seed is higher. Therefore, GMS has been exploited commercially only in few crops by few
countries. E.g. In USA used in castor while in India used for hybrid seed production of Arhar (cajanus
cajan).
2) Cytoplasmic Male Sterility:
The pollen sterility which is controlled by cytoplasmic genes is known as cytoplasmic male
sterility (CMS). Usually the cytoplasm of zygote comes primarily from the eggs cell and due to this
progeny of such male sterile plants would always be male sterile. CMS may be transferred easily to a
given strain by using that strain as a pollinator (recurrent parent) in the successive generation of backcross
programme. After 6-7 backcrosses the nuclear genotype of male sterile line would be almost identicle to
that of the recurrent pollinator strain. The male sterile line is maintained by crossing it with pollinator
strain used as a recurrent parent in backcross, since the nuclear genotype of the pollinator is identicle with
that of the new male sterile line. Such a male fertile line is known as maintainer line or ‘B’ line and ‘male
sterile line is also known as ‘A ‘ line. Cytoplasmic male sterile is not influenced by environmental factor
and it resides in maize in mitochondria.
Utilization in Plant Breeding:CMS has limited application. It cannot be used for development of hybrid,
where seed is the economic product. But it can be used for producing hybrid seed in certain ornamental
species or asexually propagated species like sugarcane, potato, and forage crops.
3) Cytoplasmic Genetic Male Sterility:
When pollen sterility is controlled by both cytoplasmic and nuclear genes is known as cytoplasmic and
nuclear genes is known as cytoplasmic genetic male sterility. Jones and Davis first discovered this type of
male sterility in 1944 in onion.
This is the case of cytoplasmic male sterility, where a nuclear genes restoring fertility in the male sterile
line is known. The fertility restore gene ‘R’ is dominant and found in certain strains of the species. This
genes restores male fertility in the male sterile line, hence is known as restores gene.

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IQC ASL
(This system includes A, B, and R lines. A line is a male sterile line, B is similar to ‘A’ in all features but
it is a male fertile and R is restore line it restore the fertility in the F1 hybrid. since B line is used to
maintain the fertility and is also referred as maintainer line. The plants would be male sterile line in the
presence of male sterile cytoplasm if the nuclear genotype is rr, but would be male fertile if the nucleus is
Rr or RR. New male sterile lines may be developed following the same procedure as in the case of
cytoplasmic system, but the nuclear genotype of the pollinator strain used in transfer must be the fertility
would be restored. Development of new restorer strain is somewhat indirect. First a restorer strain (R) is
crossed with male sterile line. The resulting male fertile plants are used as the female parent in repeated
backcrosses with the strain (C) used as the recurrent parent to which transfer of restorer gene is desired.
In each generation, male sterile plants are discarded and the male fertile plants are used as female for
back crosses. This acts as selection device for the restores gene R during the backcross programme. At
the end of back cross programme a restorer line isogenic to the strain ‘C’ would be recovered.)
Utilization in Plant Breeding: Cytoplasmic genetic male sterility is widely used for hybrid seed
production of both seed propagated species and vegetatively propagated species. It is used
Relevance of Self Incompatibility: Self incompatibility effectively prevents self pollination. As a result,
it has a profound effect on breeding approaches and objectives.
1. In self – incompatible fruit trees, it is necessary to plant two cross compatible varieties to ensure fruit
fulness. Further, cross- pollination may be poor in adverse weather condition reducing fruit set.
Therefore, it would be desirable to develop self- fertile forms in such cases.
2. Some breeding scheme. E. g Development of hybrids etc. Initially require some degree of inbreeding.
Although summating leads to inbreeding, but for the same degree of inbreeding it takes twice as much
time as selfing. Further, for the maintenance of inbred lines selfing would be necessary.
3. Self –Incompatibility may be in hybrid seed production. For this purpose
1) Two self incompatible, but cross – compatible, Lines are inter planted, seed obtained from both the
lines would be hybrid seed.
2) Alternatively, a self incompatible line may be interred planted with a self compatible line. From
this scheme, seed from only the self – incompatible line would be hybrid.
3) Schemes for the production of double cross and triple cross hybrids have also been proposed and
their feasibility has been demonstrated in the case of Brassicas
INBREEDING AND INBREEDING DEPRESSION
Definition of Inbreeding:
Inbreeding is a form of mating system in sexual organism. It implies mating together of individual that
are close to each other by ancestral or pedigree relationship.

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IQC ASL
When the individuals are closely related E. g Full sib was mating, half sib mating. The highest degree of
inbreeding is achieved by selfing. The chief effect of inbreeding is to increase homozygosity in the
progeny, which is proportionate to the degree of inbreeding. Cross – pollinated and asexually reproducing
species are highly heterozygous in nature. These species show a severe reduction in fertility and vigour
due to inbreeding (inbreeding depression). It contrast to this hybridization between unrelated strains leads
to an increased vigour and fertility (hybrid vigour or heterosis). These two aspects are of great
significance in breeding of these species. In fact heterosis and inbreeding depression may be considered
as the two opposite sides of the same coin.
Inbreeding Depression:
It refers to decrease in fitness and vigour due to inbreeding or it may be defined as the reduction or loss
in vigour and fertility as a result of inbreeding.
The most revealing impact of inbreeding is the loss of vigour and the physiological efficiency of an
organism characterised by reduction in size and fecundity. For example selfing reduces heterozygosity,
by a factor ½ in each generation. In fact the dwgree of inbreeding in any generation is equal to the degree
of homozygosity in that generation. Inbreeding depression results due to fixation of unfavourable
recessive genes in F2, while in heterosis the unfavourable recessive genes of one line (parent) are covered
by favourable dominant genes of other parent.
Man has recognised inbreeding depression for a long time. In many species marriage between closely
related ancestries have been prohibited. In hindu society perhaps presents the extreme example, where
marriages between individual related by ancestry is prohibited.
Effects of Inbreeding
Inbreeding is due to a reduction in vigour and reproductive capacity that is fertility. There is a general
reduction in the size of various plant parts and in yield. The effects of inbreeding may be summarised as
under.
a) Appearance of Lethal and Sublethal Alleles: Inbreeding to the appearance of lethal, sublethal and
subvital characteristics. Such characteristics include chlorophyll deficiencies E.g Albino, chlorine rootles
seedlings , defects in flower structure etc. generally, plants carrying such characteristics cannot
maintained and are lost from the population.
b) Reduction in Vigour: There is a general reduction in the vigour of the population. Plants become
shorter and weaker because of general reduction in the size of various plant parts.
c) Reduction in Reproductive Ability:The reproductive ability of the population decreases rapidly.
Many lines (plant progenies) reproduction poorly that they cannot be maintained.

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IQC ASL
d) Separation of the Population into Distinct Lines: The population rapidly separates into
phenotypically distinct lines. This is because of an increase in homozygosity due to which there is
random fixation of various alleles of different lines. Therefore, the lines differ in their genotype and
consequently in phenotype.
e) Increase in Homozygosity:Each line becomes increasingly homozygous following inbreeding.
Consequently, the variation within a line decreases rapidly. Ultimately, after 7 to 8 generations of selfing,
the lines become almost uniform. Since they approach complete homozygosity (> 99 percent
homozygosity). The lines, which are almost homozygous due to continued inbreeding and are maintained
through close inbreeding, are known as inbred lines or inbreds.
i) Reduction in Yield: Inbreeding generally leads to a loss in yield. The inbred lines that is able to
survive and be maintained yield much less than the open pollinated varieties from which they were
derived. In maize, the best – inbred lines yield about half as much as the open pollinated varieties from
which they were produced. In alfalfa and carrot, the reduction in yields is much greater, while in onions
and many cucurbits the reduction in yield is very small.
Degree of Inbreeding Depression
The various plant species differ considerably in their responses to inbreeding. Inbreeding depression may
range from very high to very low or may even be absent into the following four broad categories.
1) High inbreeding depression
2) Moderate inbreeding depression
3) Low inbreeding depression
4) Absence of inbreeding depression.
High Inbreeding Depression:-Several plant species, E. g alfalfa (M. sativa) carrot (D. carota) , hayfield,
tarweed etc show very high inbreeding depression. A large proportion of plants produced by selfing
shows lethal characteristics and do not survive. The loss in vigour and fertility is so great that very few
lines can be maintained after 3 to 4 generation of inbreeding. The line shows greatly reduced yields,
generally less than 25 percent of the yield of open – pollinated varieties.
Moderate Inbreeding Depression:-Many crops species, such as maize, jowar, bajara etc. shows
moderate inbreeding depression. Many lethal and sublethal types appear in the selfed progeny, but a
substantial proportion of the population can be maintained under self- pollination. There is appreciable
reduction in fertility and many line reproduce so poorly that they are lost. However, a large number of
inbred lines can be obtained, which yield upto 50 percent of the open- pollinated varieties.
Low Inbreeding Depression:-Several crop plants, E. g onion (A. cepa), many cucurbits, rye (S. cereale),
sunflower (Hannus) , hemp etc show only a small degree of inbreeding depression. Only a small

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IQC ASL
proportion of the plants show lethal or subvital characteristics. The loss in vigour and fertility is small;
rarely a line cannot be maintained due to poor fertility. The reduction in yield due to inbreeding is small
or absent. Some of the inbreds lines may yields as much as the open pollinated varieties from which they
were developed.
Lack of inbreeding Depression:-The self- pollinated species do not show inbreeding depression
although they do not show heterosis. It is because their species reproduce by self – fertilization and as a
result, have developed homozygous balance. In cost of the cross- pollinated species exhibit heterozygous
balance.

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IQC ASL
BACK CROSS METHOD
“A cross between F1 hybrid and one of its parents is known as a backcross”. It is proposed by Harian
and Pope in 1922, as a method breeding for small grains and is employed in improvement of both hybrid.
In this method two plants are selected and crossed and hybrid successively backcross to one of their
parents. As a result the grain hybrid backcross progeny becomes increasingly similar to that of the parents
to which it identical with the parent used for backcrossing. In this method the desirable variety which are
lacking in some characteristics known as a recurrent or recipient parent, while the undesirable variety on
wild variety processing only one or two desirable characteristics known as donor parent or non recurrent
parent. The objectives of this method are to improve one or two specific defects of high yielding variety.
For the successful development of a new variety, following requirements must be fulfilled.
1) A suitable recurrent parent must be available which lack in one or two characters.
2) A suitable donor parent must be available which passes the characters be transfer in highly intense
form.
3) The character to be transferred much have high heritability.
4) A sufficient number of backcrossed should be made so that the genotype of the recurrent parent is
recovered in full.
.
Application of the Backcross Method:
This method is commonly used for the transfer of disease resistant from one variety to another. But is also
suitable for the transfer of quantitative characters and is applied is both self and cross pollinated crops.
1) Intervarietal transfer of simply inherit characters such as disease resistance , seed colour , plant height
etc.
2) Intervarietal transfer or quantitative characters. Such as earliness, seed size, seed shape may be
transferred from one variety to another belongings to same species.
3) Interspecific transfer of simply inherited characters i.e disease resistance from related species to
cultivated species. Ex. Transfer of leaf and stem rust resistance from Triticum monococum to Triticum
aestivum.
4) Transfer of cytoplasm from one variety or species to another and is desirable in case of cytoplasmic
male sterility.
5) Transgressive segregation – Backcross method may be modified to produce Transgressive segregants.
6) Production of isogenic line.
Genetic Consequences of Back Crossing:
1) It results in rapid increase in homozygosity and frequency of homozygote.
2) The repeated backcrossing results in increase in frequency of desirable genotype thus the genotype of
progeny become increasingly similar to recurrent parent.
3) The gene under transfer must be maintained by selection in the back cross generation. Therefore, there
would be opportunity in each backcross generation for crossing over to occur between the gene being
transferred and tightly linked genes.

34
IQC ASL
Procedure of Back Cross Method
The plan of back cross method depend upon whether the gene being transferred is recessive or
dominant. The plan for transfer of a dominant gene is quite simple than for recessive gene.
Transfer of Dominant Gene:
Let us suppose that a high yielding and widely adopted variety ‘a’ is susceptible to stem rust (rr) and
another variety ‘b’ is poor yielding but resistant to stem rust (RR) i.e dominant to susceptibility. In this
back cross programme rust resistance trait is transfer from donor parent into a recurrent parent.
1) Hybridization:-Variety ‘A’ is crossed with variety ‘B’ in which variety ‘A’ is used as female parent
which is recurrent and variety ‘B’ is used as donor parent.
2) F1 Generation:-During the second year F1 plants are backcrossed to variety ‘A’ since all the F1 plants
will be heterozygous for rust resistance. Selection for rust resistance is not necessary.
3) First Back Cross Generation:-In the third year half of the plant would be resistant and remaining half
would be susceptible to stem rust, rust resistant plants are selected and backcross to variety ‘A’.
4) BC2 –BC6 Generation:-In each backcross generation, segregation would occur for rust resistance.
Rust resistant plant are selected and backcrossed to the variety ‘A’ selection for plant type of variety ‘A’
may be practised particularly in BC2 and BC3 generation.
5) BC6 Generation:-On an average the plant will have 98490 genes from variety A rust resistant plants
are selected and selfed, their seeds are harvested separately.
6) BC6 F2 Generation:-Individual plant progenies are grown from the selected plants. Rust resistance
once plant, which are similar to variety ‘A’ are selected and selected plants are harvested separately.
7) BC5 F3 Generation:-Individual plant progenies are grown homozygous progenies resistant to rust and
similar to plant type of variety ‘A’ harvested in bulk. Several similar progenies are mixed to constitute the
new variety.
8) Yield Test:-The new variety is tested in R.Y.T i.e replicated yield trials along with the variety ‘A’ as a
check. Plant type dates of flowering date of maturity, quality, etc are critically evaluated. The new variety
would be identical to variety ‘A’ in performance. Therefore detail yield test are not required, and the
variety may be directly released for cultivation.
Transfer of Recessive Gene:

35
IQC ASL
When rust resistant is due to a recessive gene, all the backcross cannot make one after other. After the
first backcross and after every two backcrosses F2 must be grown to identity the rust resistant plants. The
F1 and the back cross progenies are not inoculated with rust because they would be susceptible to rust.
Only F2 is tested for rust resistant.
1) Hybridization:The recurrent parent is crossed with rust resistant donor parent. The recurrent parent is
generally used as female. i.e ( rr X RR).
2) F1 Generation:-F1 plants are backcrossed to the recurrent parent.
3) BC1 Generation:-If rust resistance is recessive all the plant will be rust susceptible. Therefore, there is
no test for rust resistance. All the plants are self- pollinated.
4) BC1 (F2) Generation:-Rust resistance plants are selected and backcrossed with recurrent parent. i.e
variety ‘A’. Selection is made for the plant type and other characteristics of the variety ‘A’.
5) BC2 Generation:-No rust resistance test, plants are selected, which is identical to the recurrent parent
( A) and backcrossed with the recurrent parent.
6) BC3 Generation:-No disease resistance test. The plants are self – pollinated to raise F2. selection is
made for the plant type identical to variety ‘A’.
7) BC3 F2 Generation:-Plants are inoculated with stem rust. Rust resistant plant, similar to ‘A’ are
selected and backcrossed to variety ‘A’.
8) BC4 Generation:-No rust resistance test plants are backcrossed to variety ‘A’.
9) BC5 Generation:-No rust resistance test plants are self pollinated to raise F2 generation.
10) BC5 (F2) Generation:-Plants are subjected to rust epidemic, resistance plant for rust and having
similar characteristic of variety. ‘A’ is selected and self seed are harvested separately.
11) BC5 (F3):-Individual plant progenies are grown and subjected to rust epiphytotic selection is done
for rust resistance and for characteristics of variety ‘A’ seeds from several similar rust resistant
homozygous progenies are mixed to constitute new variety.
12) Yield Test:-Same as in case of transfer of dominant gene.
Merits of Backcross Methods:
1) The genotype of new variety is nearly identical with that of the recurrent parents.
2) It is not necessary to test the variety developed by this method, because the performance of recurrent
parent is known.
3) It is not depend upon environment.
4) It is useful for developing disease resistance var generally interspecific gene transfer.
5) It is rapid, predicted and repeatable.
6) It is useful for removing some defects such as abnormality, disease resistant etc.
Demerits of Backcross:
1) New variety cannot be superior to the recurrent parent except foe the character transfer from donor
parents.

36
IQC ASL
2) Undesirable genes may also transferred to the new variety.
3) Hybridization has to be done for each backcross so time required is more.
4) Does not permit combination of genes from more than two parents.
Achievement:
Backcross method has been widely used for the development of disease resistant varieties in both self and
cross pollinated crops. Cotton: Gossypium herbaceum var. V-797, Digvijay, Vilalpa and Kalyan. Wheat-
Kharchia 65, NP-853, NI-5439 etc.
Heterosis
The superiority of F1 hybrid over both its parents in terms of yield or some other characters or
heterosis is increased vigours, growth, yield or function of a hybrid over the parents, resulting from
crossing of genetically unlike organisms.
The term heterosis was first coined by Shull in 1914. Generally heterosis manifested as an
increase in vigour, size, growth, yield or some other characteristics. But in some cases, hybrid may be
inferior to the weaker parent this is also regarded as heterosis. The superiority of F1 is estimated over
average of the two parents (mid parent). This practise has found some acceptance particularly in the
practical studies. However, in practical plant breeding the superiority of F1 over mid parent is of no use
since it does not offer the hybrid any advantage over the better parent. Therefore, average heterosis is of
little or no use to the plant breeder. More generally, heterosis is estimated over the superior parent such
heterosis is referred as heterosis. The term heteroecism is not commonly used since most breeders regard
this to be only case of heterosis and referred to as such i.e Heterosis.
However, the commercial usefulness of a hybrid would primarily opened on its performance in
comparison to the best commercial variety. In many cases the superior parent may be inferior to the best
commercial variety. In such cases, it will be desirable to estimate heterosis in relation to the best
commercial variety is commonly known as economic or useful heterosis. Economic heterosis is the only
estimate of heterosis, which is of commercial or practical value in 1944. Powers suggested that, the term
heterosis should be used only when the hybrid is either superior or inferior to both the parents.
Theories of Heterosis
There are two main theories which have been used to explain the mechanism of heterosis. One is the
dominance hypothesis and the second is overdominace hypothesis. The epistasis is also considered to be
associated with heterosis. Thus, there are three possible genetic causes of heterosis viz.
1)Dominance
2)Over dominance
3) Epistasis

37
IQC ASL
1) Dominance Hypothesis:
This theory was proposed by Davenport (1908) Bruce (1910) and Keeble and Pellew (1910). This
is the most widely accepted hypothesis of heterosis. According to this hypothesis, heterosis is the result of
the superiority of dominant alleles, when recessive alleles are deleterious; here the deterious recessive
genes of one parent are hidden by the dominant genes of another parent and the hybrid exhibits heterosis.
Both the parents differ for dominant genes. Suppose genetic constitution of one parent is AABBccdd and
that of another as aabbCCDD. A hybrid between these two parents will have four dominant genes and
exhibit superiority over both the parents which have two dominant genes each. Thus heterosis is directly
proportional to the number of dominant genes contributed by each parent.
AABBccdd X aabbCCDD -------) AaBbCcDd
Parent 1 Parent 2 Hybrid
(one parent may have one set of dominantgenes and the other parent may have yet other set of
dominantgenes. Crossing may bring together dominant genes in F 1 generation from both parents. As a
result, F1 hybrids have more increased vigour than their parents. Suppose one parenthas the genotype
KKggPnnRR and theother parent has the genotype kkGGp pNNrr for ear length. Here,one parent has
three dominant genes for ear length and the otherparent has two dominant genes for that trait.
Hybridization bringsout heterozygosity in the F1 individuals and hence all dominant genes are brought
together the genotype of f1 will be KkGgPpNnRr So the F 1 individuals show increased ear length than
both of their
ParentsI X Parent II
KKggPPnnRR kkGGppNNrr
K+P+R= 15 k+p+r= 3
g+n=2 G+N=10
17cms 13cms
Kk Gg Pp Nn Rr
(F1 hybrid)
[K + G + P + N + R = 25 cms]
If each of the dominant genes contributes 5cms ear length and each of recessive genes contributes
1 cms ear length, parent I shows1 7cms length and the parent II shows 1 3cms ear length. Fl hybrids have
five dominant genes so that they produce 25cms long ears.Thus crossing brings togecher dominant genes
to produce hybridvigourin Fl individuals.
2) Overdominace Hypothesis:
It was independently proposed by Shull and East in 1908 and supported by Hull ( 1945). This theory is
called by various names such as stimulation of heterozygosis, cumulative action of divergene alleles,
single gene heterosis, super dominance and over dominance. Though this theory was proposed by Shull

38
IQC ASL
and East in 1908, the overdominace was coined by Hull in 1945 working on maize. This term is now in
common use.
According to this hypothesis is the result of superiority of heterozygote over its both homozygous
parents. Thus heterosis is directly proportional to the heterozygosis.
1) Production of superior hybrid substances in heterozygote is completely different from either of the
homozygous products.
2) Greater buffering capacity in the heterozygote resulting from cumulative action of divergent alleles of
stimulation of divergent alleles. East in 1936 further elaborated this theory by proposing a series of alleles
a1,a2,a3,a4 ----- of gradually increasing divergence in function. Thus a combination of more divergent
alleles will exhibit higher heterosis than less divergent combinations. For example, combination of a1, a4
will exhibit higher heterosis as compared to combination as a1, a2, a3 and a4. Overdominace has been
reported in barley. In maize, available evidence suggest that if overdominace occurs, it is either infrequent
in occurrence or small in magnitude. Dominance and overdominace hypothesis have some similarities
and some dissimilarity.
3) EPISTASIS:
Epistasis refers to interaction between alleles of two or more different loci. It is also known as non-allelic
interaction. The non-allelic interaction is of three type’s viz. additive X additive, dominance X dominance
and heterosis has positive association with the presence and magnitude of non allelic interaction.
Epistasis, particularly that involves dominance effects (dominance X dominance) may contribute to
heterosis. This has been observed in cotton and maize. Epistasis can be detected or estimated by various
biometrical models.
Manifestation (Effects) of Heterosis:
1) Increase Yield:-Heterosis is generally expressed as an increase in the yield of hybrid and may be
measured in terms of grain, fruit, seed, leaf, tubers, etc.
2) Increased Reproductive Ability:-Hybrids exhibiting heterosis show an increase in fertility or
reproductive ability.
3) Increase in Size and General Vigour:-The hybrids are generally more vigour, healthier and faster
growing.
4) Better Quality:-In many cases, hybrid show improved quality. Ex. In Onion keeping quality.
5) Earlier Flowering and Maturity:-Hybrids are earlier in flowering and maturity than the parents. Ex.
Tomato.

39
IQC ASL
6) Greater Resistant to Disease and Pests:-Hybrid exhibits a greater resistance to insect of disease than
parents.
7) Greater Adaptability:-Hybrids are more adopted to environmental changes than inbreds.
8) Faster Growth Rate:-Hybrids shows faster growth rate than their parents but the total size may be
comparable to that of the parent.
9) Increase in Number of Plant Parts:-In some cases, there is an increase in the number of nodes,
leaves and other plants parts, but the total plant size may not be larger.
Use of Heterosis in Plant Breeding:
Heterosis is exploited through the development of hybrid. It is commercially exploited in seed
production of cross pollinated crops like Jawar, maize, bajara, onion, and cucurbit. It has been also used
in some self- pollinated species such as Rice, wheat, tomato, and brinjal, etc.

40
IQC ASL
Ideotype Breeding
Ideotype breeding or plant type breeding can be defined as a method of crop improvement which
is used to enhance yield potential through genetic manipulation of individual plant characters are chosen
in such a way that each character contributes towards increased economic yield. The term Ideotype was
first proposed by Donald in 1968 working on wheat. The main points about Ideotype are given below:
1. Crop Ideotype refers to model plants or ideal plant type for a specific environment.
2. Ideotype differs from Ideotype
3. Donald included only morphological characters to define an Ideotype of wheat, subsequently,
physiological and biochemical traits were also included for broadening the concept of crop Ideotype.
Main features of Ideotype breeding ;
1. Emphasis on Individual Trait:-In Ideotype breeding, emphasis is given on individual morphological
and physiological trait which enhances the yield. The value of each character is specified before initiating
the breeding work.
2. Includes Yield Enhancing Traits:-Various plant characters to be included in the Ideotype are
identified through correlation analysis. Only those characters which exhibit positive association with
yield are included in the model.
3. Exploits Physiological Variation:-Genetic difference exists for various physiological characters such
as photosynthetic efficiency. Photo respiration, nutrient uptake, etc. Ideotype breeding makes use of
genetically controlled physiological variation in increasing crop yields, besides various agronomic traits.
4. Slow Progress:-Ideotype breeding is a slow method of cultivar development, because incorporation of
various desirable characters from different sources into a single genotype takes long time. Moreover,
sometimes undesirable linkage affects the progress adversely.
5. Selection:-In Ideotype breeding selection is focussed on individual plant character which enhances the
yields.
6. Designing of Model:-In Ideotype breeding, the phenotypes of new variety to be developed is specified
in terms of morphological and physiological traits in advance.
7. Interdisciplinary Approach:-Ideotype breeding is in true sense an interdisciplinary approach. It
involves scientist from the disciplines of genetics, breeding, physiology, pathology, entomology etc.
8. A Continuous Process:-Ideotype breeding is a continuous process, because new Ideotype have to be
developed to meet changing and increasing demands. Thus development of Ideotype is a moving target.

41
IQC ASL
Ideotype breeding differs from traditional breeding in the sense that values for individual traits are
specified in case of Ideotype breeding, whereas such values are not fixed and then efforts are made to
achieve such model. In traditional breeding, such models are not developed before initiation of breeding
programmes. There are several differences between traditional breeding and Ideotype breeding.
Steps in Ideotype Breeding
Ideotype breeding consists of four important steps, viz:
1) Development of conceptual theoretical model,
2) Selection of base material,
3) Incorporation of desirable characters into single genotype, and
4) Selection of ideal or model plant type. These steps are briefly discussed below:
1. Development of Conceptual Model: -Ideotype consists of various morphological and physiological
traits. The values of various morphological and physiological traits are specified to develop a conceptual
theoretical model. For Example, value for plant height, maturity duration, leaf size. Leaf number, angle of
leaf, photosynthetic rate etc. are specified. Then efforts are made to achieve this model.
2. Selection of Base Material:-Selection of base material is an important step after development of
conceptual model of Ideotype. Genotype to be used in devising a model plant type should have broad
genetic base and wider adaptability (Blixt and Vose. 1984) so that the new plant type can be successfully
grown over a wide range of environmental condition with stable yield. Genotypes for plant stature,
maturity duration, leaf size, and angles are selected from the global gene pool of the concerned crop
species. Genotypes resistant or tolerant to drought, soil salinity, alkalinity, disease and insects are selected
from the gene pool with the cooperation of physiologist, soil scientist, pathologist and entomologist.
3. Incorporation of Desirable Traits:-The next important step is combining of various morphological
and physiological traits from different selected genotypes into single genotype. Knowledge of the
association between various characters is essential before starting hybridization programme, because it
help in combining of various characters. Linkage between procedures, viz single cross, three way cross,
multiple cross, backcross, composite crossing. E.g. Mutation breeding, heterosis breeding, etc. are used
for the development of ideal plant types in majority of field crops. Backcross technique is commonly used
for transfer of oligogenic traits from selected germplasm lines into the background of an adapted
genotype.
4. Selection of Ideal Plant Type:-Plant combining desirable morphological and physiological traits are
selected in segregating population and intermated to achieve the desired plant type. Morphological
features are judged through visual observation and physiological parameters are recorded with the help of
sophisticated instruments. Screening for resistance to drought, soil salinity, alkalinity, disease and insects

42
IQC ASL
is done under controlled conditions. This task is completed with the help of scientist from the disciplines
of physiology, soil science, pathology and entomology. Finally, genotypes combining traits specified in
the conceptual model are selected, multiplied, tested over several locations, and released for commercial
cultivation.
Crop Ideotype
The crop Ideotype consists of several morphological and physiological traits which contribute for
enhanced yield or higher yield than currently prevalent crop cultivars. The morphological and
physiological features of crop Ideotype is required for irrigated cultivation or rainfed cultivation. Ideal
plant whether the Ideotype is required for irrigated cultivation or rainfed cultivation. Ideal plant types or
model plants have been discussed in several crops like wheat, rice, maize, barley, cotton, and bean. The
important features of Ideotype for some crops are briefly described below:
Wheat:
The term Ideotype was coined by Donald in 1968 working on wheat. He proposed Ideotype of wheat with
following main features.
1. A short strong stem. It imparts lodging resistance and reduces the losses due to lodging.
2. Erect leaves. Such leaves provide better arrangement for proper light distribution resulting in high
photosynthesis or CO2 fixation.
3. Few small leaves. Leaves are the important sites of photosynthesis, respiration, and transpiration. Few
and small reduce water loss due to transpiration.
4. Larger ear. It will produce more grains per ear.
5. Presence of awns. Awns contribute towards photosynthesis.
6. A single culm.Thus, Donald included only morphological traits in the Ideotype. However, all the traits
ere based on physiological consideration. Finally (1968) doubted the utility of single clum in wheat
Ideotype. Considered tillering as important features of wheat flag type a wheat plant with moderately
short but broad flag leaf, long flag leaf sheath, short ear extrusion with long ear, and moderately high
tillering capacity should give yield per plant (Hsu and Watson, 1917). Asana proposed wheat Ideotype for
rainfed cultivation. Recent workers included both morphological and physiological characters in wheat
Ideotype.
Rice:
The concept of plant type was introduced in rice breeding by Jennings in 1964, through the term
Ideotype was coined by Donald in 1968. He suggested that the rice an ideal or model plant type consists
of 1) Semi dwarf stature. 2) High tillering capacity, and 3) Short, erect, thick and highly angled leaves

43
IQC ASL
(Jennings, 1964, Beachell and Jennings, 1965). Jennings also included morphological traits in his model.
Now emphasis is also given to physiological traits in the development of rice Ideotype.
Maize:
In 1975, Mock and Pearce proposed ideal plant type of maize. In Maize , higher yields were obtained
from the plants consisting of 1) Low tillers, 2) Large cobs, and 3) Angled leaves for good light
interception. Planting of such type at closer spacings resulted in higher yields.
Barley:
Rasmusson (1987) reviewed the work on Ideotype breeding and also suggested ideal plant type of six
rowed barley. He proposed that in barley, higher yield can be obtained from a combination of 1) Short
stature, 2) Long awns, 3) High harvest index, and 4) High biomass. Kernel weight and kernel number
were found rewarding in increasing yield.
Achievements in Ideotype Breeding
Ideotype breeding has significantly contributed to enhanced yields in cereals (Wheat and rice) and
millets. (Sorghum and pearl millet) through the use of dwarfing genes, resulting in green revolution.
Semidwarf varieties of wheat and rice are highly responsive to water use and nitrogen application and
have wide adaptation. These qualities have made them popular throught the world. Spontaneous
mutations have played significant role in designing new plant types in wheat and rice. The Norin 10 in
wheat and Dee-geo-Woo-gene in rice are the source of dwarfing genes. These sources of dwarfing genes
were obtained as a result of spontaneous mutations. Several high yielding Semidwarf varieties have been
evolved in wheat and rice through the use of respective dwarf mutant. The Norin-10, dwarfing gene in
wheat, the Dee-geo-woogen dwarfing gene in rice and the genic cytoplasmic male sterile system in
sorghum and pearl millet laid the foundation of green revolution in Asia (Swaminathan, 1972). Thus,
Ideotype breeding has been more successful for yield improvement in cereals and millets than in other
crops.
In rice, the improved plant type includes,
1) Erect, short and thick leaves.
2) Dwarf stature,
3) Light leaf sheath,
4) High tillering capacity,
5) Responsiveness to high levels of nitrogen, and
6) High harvest index,
Examples of Semidwarf varieties of rice are IR-8, IR-20, TN1 etc. The Chinese variety Dee-geo-woogen
is the source of dwarfing gene in all these varieties.
In wheat, the improved plant type included,
1) Short and still straw,

44
IQC ASL
2) Insensitivity to photoperiods,
3) High response to nitrogen application,
4) High harvest index,
5) Resistance to different rusts.
Merits and Demerits of Ideotype Breeding
Merits:
1. Ideotype breeding is an effective method of enhancing yield through manipulation of various
morphological and physiological crop characters. Thus, it exploits both morphological and physiological
variation.
2. In this method of various morphological and physiological traits are specified and each character or
trait contributes towards enhanced yield.
3. Ideotype breeding involves experts from the discipline of plant breeding, physiology, biochemistry,
entomology and plant pathology. Each specialist contributes in the development of model plants for traits
related to his field.
4. Ideotype breeding is an effective method of breaking yield barriers through the use of genetically
controlled physiological variation for various characters contributing towards higher yield.
5. Ideotype breeding provides solution to several problems at a time like disease, insect and lodging
resistance, maturity duration, yield and quality by combining desirable genes for these traits from
different sources into a single genotype.
6. It is efficient method of developing cultivars for specific or environment.
Demerits:
1. Incorporation of several desirable morphological and physiological and disease resistance traits from
different sources into a single genotype is a difficult task. Sometimes, combining of some characters is
not possible due to tight linkage between desirable and undesirable characters. Presence of such linkage
hinders the progress of Ideotype breeding.
2. Ideotype breeding is a slow method of cultivar development, because combining together of various
morphological and physiological features from different sources takes more time than traditional breeding
where improvement is made in yield and one or two other characters.
3. Ideotype breeding is not a substitute for traditional or conventional breeding. It is a supplement to the
former.
4. Ideotype is a moving object which changes with change in knowledge, new requirements, national
policy, etc. Thus new Ideotype have to evolved to meet the changing and increasing demands of
economic products.

45
IQC ASL
Introduction Resistance Breeding
pesticides).
Stress refers to adverse conditions for crop growth and production imposed by either
environmental factors or biological factors, thus stress is of two types, viz. 1) Biotic and 2) Abiotic. The
stress that is caused by biological agents or factors, such as disease, insects and parasitic weeds, is known
as biotic stress. When the stress is caused by environmental factors or non biological factors, it is
referred to as abiotic stress. Abiotic stress is generally caused by factors like deficiency or excess of
nutrition, moisture, temperature and light; presence of harmful gases or toxicants; and abnormal soil
conditions such as salinity, alkalinity and acidity. All crop plants suffer from both biotic and abiotic
stresses to varying degrees. This chapter deals with breeding for resistance to disease.
Genetic Resistance
Genetic resistance refers to those heritable features of a host plant that suppress or retard development of
a pathogen or insect. In other words, genetic resistance is the ability of some genotypes to give higher
yields of good quality than other varieties at the same initial level of pest infestation under similar
environmental conditions, thus resistance is defined in relation to susceptible varieties. Genetic
resistances are considered as a major form of biological control of biotic stresses. Main features of
genetic resistances are given below:
1. Genetic resistance is governed by nuclear genes or cytoplasmic genes or both in other words; genetic
resistance is an inbuilt mechanism or inherent property.
2.Genetic resistance is measured in relation to susceptible varieties or genotypes.
3. Breeding of resistant cultivars takes into account the genetic variability of both pest and host plant.
4. The resistant variety may become susceptible after few years due to formation of new races of
pathogen or new biotypes of an insect
5. Breeding for disease and insect resistance differs from breeding for higher yield. There is triangular
interaction is between genotype and environment only.
Types of Genetic Resistance:
1. Vertical or Specific Resistance:
Specific resistance of a host to the particular race of a pathogen is known as vertical resistance. This type
of resistance is governed by one or few genes and, therefore , is referred as oliogenic(a heritable
characteristic: controlled by a few genes.) resistance. When the resistance is controlled by single gene, it
is called monogenic resistance. Since vertical resistance controls only one race of a pathogen, it is also
termed as specific resistance. Because of its simple inheritance, it is known as major gene resistance. As
the controlling genes have distinct effect, it is also known as major gene resistance. The host with vertical
resistance controls only one race; therefore, it is also known as non-uniform resistance. Main features of
vertical resistance are given below:

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