Plant Breeding Full PPT (secA)This is course material for plant breeding..pdf

Chapter 1: introduction and history of plant breeding
I. introduction
What is plant breeding & why plant breeding
The goals of plant breeding
Overview of the basic steps in plant breeding
The art and science of plant breeding
Achievements plant breeder & breeding industry
II. History of plant breeding
Origins of agriculture and plant breeding
Plant manipulation efforts by early civilizations
pioneers of the theories and practices of modern plant breeding
 History of plant breeding technologies/techniques
 Plant breeding in the last half century

I. Introduction
What is plant breeding?
 Agriculture is deliberate planting plants and herding animals.
 This human discovery has impact on society and the environment.
 Plant breeding is branch of agriculture focuses on manipulating
plant heredity to develop improved plant for human use
 The term “plant breeding” is often used synonymously with “plant
improvement” in modern society
 When technology advances, breeders are increasingly able to
accomplish amazing plant manipulations,

What is plant breeding? CON”t
 professionals who conduct plant breeding called plant breeders.
 Plant breeders specialize different groups of plants.
Some focus on field crops (e.g. wheat, maize),
horticultural food crops (e.g., vegetables),
ornamentals (e.g., roses, pine trees),
fruit crops(e.g., citrus, apple),
foragespecies. (e.g., Bluegrass, fescue)
 crops (e.g., alfalfa,grasses),
 breeders tend to specialize on specific species in these
groups (e.g., corn breeder, potato breeder).
they improve the species of their choice.
principles & concepts of breeding are generally
applicable to breeding all plant species.

Why breed plants?
 Plants provide food, feed, fiber, pharmaceuticals & shelter
 plants also used for aesthetic in the landscape and indoors.
so, manipulating of plant perform according to needs of society:
 Addressing world food and feed quality needs
 Addressing food supply needs for a growing world population
 Need to adapt plants to environmental stresses
 Need to adapt crops to specific production systems
 Developing new horticultural plant varieties
 Satisfying industrial and other end-use requirements

Why breed plants? CON’T
Addressing world food and feed quality needs
 Food is the most basic of human needs.
 Plants are the primary food producers in the ecosystem
 Without plant, presence of higher organisms’ life is impossible.
 PB Address world food needs by enhance the value of food crops,
via improving their yield, their disease resistance and the
nutritional quality of their products,


Addressing food supply needs for a growing world population
 As world population increases, need for agricultural production
system increase.
 three billion people will be added to world population in next
three decades, requiring an expansion in world food supplies to meet
the projected needs.
 Unfortunately, land for farming is scarce. So, we have to increase
productivity per existing area via PB

Need to adapt plants to environmental stresses
 Due to climatic change modifying crop production based on
environment is needed
This means that new cultivars of crops need to be bred for new
production environments.
For example, development and use of drought resistant cultivars
is beneficial to crop production in areas of inconsistent rainfall
 Generally, Breeders need to develop new plant types that can resist
various biotic & abiotic stresses in the production environment

Need to adapt crops to specific production systems
 Breeders need to produce plant cultivars for specific production
systems. For example,
crop cultivars must be developed for rain-fed or irrigated
production ,mechanized or non-mechanized production.
In the case of rice, separate sets of cultivars are needed for
highland production and for flooded field production.
In organic production systems where pesticide use is restricted,
producers need insect & disease resistant cultivars

Developing new horticultural plant varieties
 horticultural production industry succeeds on the development of
new varieties through plant breeding.
 Aesthetics is of major importance to horticulture.
 Periodically, ornamental plant breeders release new varieties that
exhibit new colors & other morphological features (e.g., height,
size, shape).
 Also, breeders develop new varieties of vegetables and fruits with
superior yield, nutritional qualities, adaptation, & general appeal.

Satisfying industrial & other end-use requirements
 Processed foods are a major item in the world food supply system.
 Quality requirements for fresh product consumption are different
from those for the food processing industry.
 E.g, there are table grapes and grapes bred for wine production.
 Different markets have different needs that plant breeders can address
For example, potato is a multipurpose crop used for food and
industrial products.
D/t varieties are being developed by breeders for baking,
cooking, fries (frozen), chipping, and starch.
These cultivars differ in size, specific gravity, sugar content,
etc among other properties.

Goals of plant breeding & genetic manipulation of plant
characteristics
The goals of plant breeding
 Breeders aim to make crop producer’s job easier and more
effective in various ways:
modify plant structure: resist lodging and facilitate mechanical
harvesting.
develop plants that resist pests: farmer
does not apply pesticides, or applies smaller amounts
less environmental pollution from agricultural sources.
develop high yielding & high quality varieties
farmer can produce more for market to meet consumer
demands & improving income.
develop foods with higher nutritional value and more flavorful
Higher nutrition reduced illnesses in society

genetic manipulation of plant characteristics
 work of Mendel & others established that plant traits are controlled
by hereditary factors or genes.
These genes are expressed in an environment to produce a trait.
then to change a trait or its expression, we change its genotype,
and/or environment that it is expressed.
Changing environment needs modifying growing conditions.
This may be achieved through agronomic approach; like
application of production inputs (e.g., fertilizers, irrigation).
When supplemental environmental factors are removed, the
expression of the plant trait reverts to the original status
 plant breeders also modify plants via the expression of certain
selected traits by targeting specific genes.
Thus produces an alteration that permanently transfer from one
generation to the next.

Overview of the basic steps in plant breeding
 Plant breeding has come a long way
 Plant breeding methods & tools keep changing as technology
advances.
 Consequently, for convenience/ suitability plant breeding
approaches may be categorized into two general types:
conventional
 unconventional.

Overview of the basic steps in plant breeding CON’T
Conventional approach
 it is also called traditional or classical breeding.
 This approach uses older tools.
 Crossing two plants (hybridization) is the primary technique for
creating variability in flowering species.
 Various breeding methods are used to select most desirable
recombinant.
 selected genotype is evaluated for performance before release
 conventional approach remains pillar of plant breeding industry.
 It is accessible to average breeder & is relatively easy to conduct
compared to unconventional.

Unconventional approach
 uses superior technologies for breed that may not possible by
conventional methods.
 requires special technical skills and knowledge.
 expensive to conduct.
 The advent rDNA technology gave breeders a new set of powerful
tools for genetic analysis and manipulation.
 Gene transfer can now be made across natural biological barriers
 Molecular markers are available to aid the selection process to
make the process more efficient and effective.
These two basic breeding approaches considered as
complementary rather than independent approaches.

basic steps in plant breeding
 For both approach, breeder follows 5 general steps in conducting a
breeding project.
1. Set Objectives.
 breeder 1st set a clear objective to initiate breeding program.
 In selecting breeding objectives, breeders need to consider:
A. Considering grower: the cultivar profitability (need for high
yield, disease resistance, early maturity, lodging resistance).
B. Considering processor : consider the quality of cultivars when use
as row material (e.g., canning qualities, fiber strength).
C. Considering consumer preference (e.g., taste, high nutritional
quality, shelf life).

2. Germplasm Collection
 It is impossible to improve plants without genetic variability.
 Germplasm ( GP) considers as blood stream of breeders
 Once the objectives seated, breeder assembles germplasm to
initiate breeding program.
 new variability can be created through crossing of selected parents,
inducing mutations, or using biotechnological techniques.
 base population used to initiate a breeding program must include
the gene(s) of interest.
That is, you cannot breed for disease resistance, if disease
resistance gene does not occur in the base population.

3. Selection
 After creating or assembling variability, the next task
 select individuals with the desirable genotype to advance and
increase in order to develop potential new cultivars.
 Selection methods may be standard selection or breeding methods
suitable for the species and the breeding objective(s).

4. Evaluation
 Different experts like Agronomists may participate in this stage
 since it is comparing of superior candidate genotypes to select one
for release as a cultivar, evaluation is also a selection process,
 To identify the most promising one for release as a commercial
cultivar potential cultivars evaluate:
 in the field, sometimes at d/t locations and over several
years,
5. Certification and cultivar release.
 Before a cultivar is released, it is processed through a series of steps,
called the seed certification process,
increase experimental seed and to obtain approval for release
from designated crop certifying agency in the country.

The art, science & technology concept of PB
Art and the concept of the “breeder’s eye”
 Early plant breeders depended primarily on perception, skill, and
judgment in their work.
These are still desirable in modern day plant breeding.
 A good breeder should have a keen/strong sense of observation.
 Breeders have to discriminate among thousands of plants in a
population to select a small promising.
 Right now Visual selection is an art, but it can be facilitated by
selection aids such as genetic markers

The art and science of plant breeding CON’T
The scientific disciplines of plant breeding
 As knowledge & technology advances, modern breeders are
increasingly depending on science
 At the minimum, a plant breeder should have a good understanding
of genetics & principles and concepts of plant breeding.
 However, plant breeding as an applied science art is important to
the success achieved by a plant breeder.
 Science & technology component of modern plant breeding is
rapidly expanding.

Genetics
 Genetics is principal scientific basis of modern PB
 Since plant breeding is about targeted genetic modification of plants.
The science of genetics enables plant breeders to predict the
outcome of genetic manipulation of plants.
 The techniques and methods employed in breeding are determined
based on the genetics of the trait of interest
for example, number of genes coding for it and gene action.
Botany:
 Plant breeders need to understand the reproductive biology of their
plants as well as their taxonomic attributes.
to know if plants to be hybridized are cross-compatible,
about flowering habits to design most effective crossing
program.

Plant physiology:
 Physiological processes indicate d/t phenotypes observed in plants.
 Genetic manipulation alters plant physiological performance
biotic and abiotic stress are sources of physiological stress
when they occur at unfavorable levels.
So, Plant breeders need to understand stress effect on plant
physiology to develop cultivars that can resist the stress
Agronomy:
 breeders conduct their work in controlled or field environments.
 An understanding of agronomy (the art and science of producing
crops and managing soils) will help the breeder
 to provide appropriate cultural conditions & selection in field.
Without proper nurturing, genetic potential of an improved
cultivar would not be realized.

Pathology & entomology:
 Disease resistance breeding is a major plant breeding objective.
 breeders need to understand biology of pathogen against which
resistance is being required.
kind of cultivar to breed, methods to use in breeding &
evaluation depend on t kind of pathogen
e.g., its races or variability, pattern of spread, life cycle,
and most suitable environment.
Statistics:
 Breeders need to know principles of research design & analysis.
for effectively designing field & laboratory studies
To evaluate genotypes & release at end of breeding program.

biotechnology:
 In this era of biotechnology, breeders need to be familiar with
molecular basis of heredity like:
procedures of plant genetic manipulation at molecular level
use of molecular markers and gene transfer techniques.
Plant breeding team
 the breeder cannot be an expert in all of them.
 Modern plant breeding is more team work than solo effort.
 The teams have experts in all these key disciplines,
each one contributing to development & release of a successful
cultivar.

Technologies for plant breeding
 There are d/t technologies used in modern plant breeding
 Some of these tools are used to
to transfer genes from one genetic background
 to create variability for breeding.
facilitate the breeding process, for example, identifying
individuals with the gene(s) of interest (Selection).

Technologies for plant breeding …

Achievements plant breeder & breeding industry
Achievements plant breeder
 The achievements of plant breeders are numerous, but may be
grouped into several major areas of impact:
yield increase
enhancement of compositional traits
crop adaptation
the impact on crop production systems
breeding industry
 In different countries public and privet sectors are involving in
plant breeding program at national and international level.

1.2. History of plant breeding
 Origins of agriculture and plant breeding
 Plant manipulation efforts by early civilizations
 pioneers of the theories and practices of modern plant breeding
 History of plant breeding technologies/techniques
 Plant breeding in the last half century

Origins of agriculture and plant breeding
 Agriculture is a human creation that continues to impact society
and the environment.
 The tools & methods used by plant breeders developed &
advanced through the years.
 There are milestones in plant breeding technology
 plant breeding started after the invention of agriculture,
when people of primitive switched from a lifestyle of hunter–
gatherers to sedentary producers of selected plants & animals.

Origins of agriculture and plant breeding CON’T
 Fertile area in Middle East is believed to be foundation of
agriculture,
where deliberate tilling of the soil, seeding and harvesting
occurred over 10 000 years ago.
This was a gradual process which plants transformed from
wild to domesticated varieties.
 During this period humans discovered the traditional and most
basic plant breeding technique ( i.e. selection)
 In the beginnings of PB,
germplasm source was naturally occurring variants and
wild relatives of crop species.
selection was based solely on awareness, skill judgment of
operator

 In PB beginning time there are two non personally recognized
group of people (Unknown breeder) who impacted plant
improvement.
 These two Unknown breeder groups are:
 the “farmer-breeder”
The “no name” breeder
The “no name” breeder
 One of the common practices in modern PB is to refer to germplasm
whose source, name or is unknown as simply “No Name”.
 This unexpected acknowledgement appears to clear the breeder of
any deliberate and determined violation on intellectual property.

Farmer breeder
 They are leaded by people who unknowingly and indirectly
manipulated the nature of plants to their advantage.
 “farmer-breeders”, continues to impact world crop production today.
 farmers depend on their keen observation to save seed from
selected plants for planting the next crop.
 Performance and demand are two key factors in the decision making
process.
 Over time, farmers create varieties of crops
These creations are called farmer-selected varieties and
sometimes landraces

Plant manipulation efforts by early civilizations
 From historical records in early civilizations some of communities
engaged in basic plant manipulations without knowledge of plant
heredity.
 some ancient practices indicate that plant manipulation beyond
phenotypic selection among natural variability occurred.
Babylonians applied pollen to the pistils of female date palms to
produce fruit.
The Assyrians did likewise in about 870 BC, artificially
pollinating date palms.

pioneers of the theories & practices of plant breeding
Early pioneers of plant breeding
 Plant breeding as we know it today began in earnest in the
nineteenth century.
 Prior to this era, a number of groundbreaking discoveries and
innovations paved the way for scientific plant manipulation.
 Some of the early pioneers of plant breeding include the following:
Rudolph Camerarius (1665–1721).
Joseph Gottlieb Koelreuter (1733–1806).
Louis de Vilmorin (1902–1969).
Thomas Andrew Knight (1759–1838).
Carl Linnaeus (1707–1778).
Charles Darwin (1809–1882).
Gregor Mendel (1822–1884).
Luther Burbank (1849–1926).

Later pioneers and trailblazers
 Since the beginning of the nineteenth century, there has been an
explosion of knowledge in PB and its allied disciplines.
 Some of these innovations discovered by the following scientists:
Nikolai I. Vavilov. identified eight areas of the world which he
designated centers of diversity of crop species or centers of
origin of crops.
H.J. Muller. The pioneering experiments by Muller (1927) showed
that it is possible to alter the effect of gene Using X-rays.
H.H. Hardy and W. Weinberg: They independently demonstrated
that in a large random-mating population, both gene and
genotypic frequencies remained unchanged from one generation
to the next, in the absence of change agents like mutation,
migration and selection.
This later became known as the Hardy–Weinberg equilibrium
or law.

Watson and Crick:
 understanding of heredity that underlies the ability of plant breeders
to effectively manipulate plants at the molecular level to develop new
cultivars, depends on the important work of Watson and Crick.
Their discovery of the double helical structure of the DNA
molecule laid foundation for the understanding of the
chemical basis of heredity.
Norman Borlaug:
 In modern era of agriculture, Norman Borlaug deserves mention,
according to a methodology driven by his personal philosophy– the
first agriculturalist to be so recognized in the Green Revolution.

History of plant breeding technologies/techniques
 Modern plant breeding is an art and a science.
 creation (or assembling) of variation and discriminating (selecting)
two key activities in plant breeding to meet the breeding objectives.
Consequently, advances in plant breeding technologies and
techniques focus on facilitating and making these two distinct
activities more efficient and cost effective.

History of plant breeding technologies/techniques CON’T
Technologies/techniques associated with creation of variation
 Variation may be natural in origin or artificially
 breeders used various technologies & techniques for desired
variation.
A. Artificial pollination (controlled pollination)
 It is deliberate transfer of pollen from the flower (anther) of one
plant to the flower (stigma) of another plant ( an ancient practice).
 These ancient cultures did this without the benefit of knowing the
underlying science of pollination and fertilization.
 Artificial pollination is used in a variety of ways in modern plant
breeding.
 Naturally cross-pollinating species can be artificially self-pollinated
to create variability

B. Hybridization(crossing)
 It is commonly used techniques in modern plant breeding to create
variation in genetically different plants.
 F2 is the most variable generation in which selection is often
initiated.
 Breeders working in the field often have crossing blocks where
controlled hybridization is conducted.
 Depending on the species and breeding objective, pollination may be
done manually, or with the aid of natural agents (wind, insects).

C. Tissue culture/embryo culture
 Tissue culture entails growing plants or parts of plants
in vitro under an aseptic environment.
 It has various applications in modern plant breeding.
 Regarding the generation of variation, application of tissue culture is in
rescuing embryos produced from wide crosses.
The genetic incompatibility arising from genetic distance b/n
parents in wide crosses, embryo often not produce viable seed.
 technique of embryo culture enables breeders to aseptically extract
the immature embryo and culture it into a full grown plant that
can bear seed.

D. Chromosome doubling
 To avoid a major barrier to interspecific crossing, breeders use
chromosome doubling technique to double the chromosomes
 It uses in the hybrid created to provide paring partners for successful
meiosis and restoration of fertility.
 Chromosome doubling is achieved through the application of the
chemical colchicine.

E. Bridge cross
 This technique provides an indirect way of crossing two parents
that differ in ploidy level through a transitional or intermediate
cross.
This intermediate cross is reproductively sterile and is subjected
to chromosome doubling to restore fertility.

F. Protoplast fusion
 protoplast (excluding cell wall) fusion is a technique used by
breeders to effect in vitro hybridization in situations where normal
hybridization is challenging.
 It uses to overcome barriers to fertilization associated with
interspecific crossing ( hybridization b/n potato and tomato =
pomato)
 The first successful application of this techniques occurred in 1975.

G. Hybrid seed technology/technique
 Hybridization may also be done to create the end product of a
breeding program.
 discovery of heterosis phenomenon foundation for hybrid seed
technology.
 Breeders spend resources to design and develop special genotypes
to be used as parents in producing hybrid seeds.
 Hybrid seed is expensive to produce and hence costs more than
non-hybrid seed.
 terminator technology, was introduced as a means of deterring the
unlawful use of hybrid seed.
This technology causes a farmer cannot harvest seed to the next
season’s crop).

H. Seedlessness technique
 Whereas fertility is desired in a seed-bearing cultivar, sometimes
seedless fruits are preferred by consumers.
 The observation that triploidy (or odd chromosome number set)
results in hybrid sterility led to the application of this knowledge as a
breeding technique.
Crossing a diploid (2n) with a tetraploid (4n) yields a triploid
(3n), which is sterile and hence produces no seed.
It may be large fruit

I. Mutagenesis
 Evolution is driven by mutations that arise spontaneously in the
population.
 Since the discovery in 1928 by H. Muller of the mutagenetic effects
of X-rays on the fruit fly,
the application of mutagens (physical and chemical) have been
exploited by plant breeders to induce new variation.
 Mutation breeding is a recognized scheme of plant breeding that has
yielded numerous successful commercial cultivars, in addition to
being a source of variation.

J. DNA technology
 The advent of the recombinant DNA technology in
1985 revolutionized the field of biology and enabled researchers to
directly manipulate an organism directly at the DNA level.
 Simply put, DNA or gene from an animal may be transferred into
a plant.
 A new category of cultivars, GM cultivars, has been developed
using recombinant DNA technology.
 DNA technologies and techniques are exploding at a huge rate with
cost effective.
 One of the most useful applications of DNA technology in plant
breeding is in molecular markers.

Technologies/techniques for selection
 Selection or the discrimination among variability is the most
fundamental of techniques used by plant breeders throughout the
ages.
 In some cases, individual plants are the units of selection; in other
cases, a large number of plants are chosen and advanced in
breeding program.
 With time, various strategies (breeding schemes) have been
developed for selection in breeding programs.
Selection (breeding) schemes
 The most basic of these schemes is mass selection;
 others are recurrent selection, pedigree selection, and bulk
population strategy
These selection vary depending on the plant pollination and
reproduction system

Molecular marker technology for selection
 Marker technique is essentially selection by proxy/ indirect means.
 Markers are phenotypes that are linked to genotypes (or precisely
genes of interest).
 Molecular (DNA-based) markers have superseded morphological
markers in scale of use in plant breeding.
 Marker assisted selection (MAS) is used to facilitate plant breeding

Plant breeding in the last half century
plant breeding as a discipline and practice has changed
significantly over the years.
 Changes in to the science of breeding
 Changes in laws and policies
 Changes in breeding objectives
 Changes in the creation of variability
 Changes in identifying and evaluating genetic variability
 Selecting and evaluating superior genotypes

Group Assignment: Submission date :December 07/2023
Group 1: Wheat breeding
Group 2: Corn Breeding
Group 3: Rice Breeding
Group 4: Sorghum Breeding
Group 5: Soybean Breeding
Group 6: Potato Breeding
Group 7: Cotton Breeding
Group 8: Tomato breeding
Each group should discuss the breeding of crops based on:
The economic importance of the crop.
The origin and adaptation of the crop.
The genetics and cytogenetics of the crop that impact its breeding.
The germplasm resources for breeding the crop.
The general botany and reproductive biology of the crop
 The common breeding methods used in breeding crop.

Individual assignment : Common statistical methods in plant
breeding
 Discuss the role of statistics in plant breeding.
 Discuss the application of multivariate statistics in plant breeding.
 Discuss the procedure of path analysis and its application in breeding.
• Submission date :December 14/2023

Chapter 2: Population and quantitative genetic
principles to plant breeding
population genetics principles to plant breeding
 genetics
 Genetic properties of a population
 Mathematical model of a gene pool
 Selection
 Mating designs
 Inbreeding
 population improvement
 quantitative genetics principles to plant breeding
Gene action
Variance components of a quantitative trait
Heritability

Genetics
 Genetics is the study of heredity and variation.
Heredity refers to transmission of genetic information (genes)
from parents to offspring.
Variation refers to difference among individuals of a
species for a character.
It may be due to heredity or environment.

BRANCHES OF GENETICS
 genetics classified into three branches as
1. transmission /classical genetics,
2. molecular genetics
3. population genetics.

I. Population Genetics principles to plant breeding
 Some breeding methods focus on individual plant improvement,
whereas others focus on improving plant populations.
 genetic structure of a population determines its capacity to be
changed by selection for plant improvement.
 Understanding population structure is key to deciding the plant
breeding options and selection strategies.

population genetics…
 A population is a group of sexually interbreeding individuals.
It implies that every gene within group is accessible to all
members through sexual process.
 A gene pool is total number of genes and alleles in population that
can transfer to next generation.
 population genetics is concerned how the frequencies of alleles in a
gene pool change over time.
Breeding cross-pollinated species focus improving populations
Breeding self-pollinated species focus improving individual
plant

Genetic properties of a population
 genetic properties of population influenced by four factors when
genes transfer from one generation to next :
A. population size
B. differences in fertility and viability
C. migration and mutation
D. the mating system.

Mathematical model of a gene pool
 Population genetics uses mathematical models to describe
population phenomena.
 To apply mathematical models for calculating gene frequency it is
necessary to make assumptions of:
alarge population
random mating occurs
no mutation criteria
no gene flow between this population and others,
no selective advantage for any genotype

Calculating gene frequency
 Assume a population of N diploids in which two alleles (A, a) occur
at one locus.
 Assuming dominance at the locus, three genotypes – AA, Aa, and aa
– are possible in an F2 segregating population.
 Assume genotypic frequencies are D (for AA), H (for Aa) and Q
(for aa).
 Since the population is diploid, there will be 2N alleles in it.
 The genotype AA has two A alleles, also aa genotype has two aa alleles
 The proportion or frequency of A alleles (designated as p) in the
population is obtained as follows:

Hardy–Weinberg equilibrium
 the previous alleles (A/a) will yield genotypes AA, Aa, and aa, with
the corresponding frequencies of p2, 2pq, and q2, respectively.
Consequently, p2 + 2pq + q2= 1 or 100%
 This mathematical relationship is called Hardy–Weinberg
equilibrium.
They showed frequency of genotypes in a population depends
on frequency of genes/alleles in preceding generation, not
on frequency of the genotypes.

Factors affecting changes in gene frequency
 Gene frequency in a population may be changed dispersive &
systematic process.
dispersive process, change only in amount, not direction.
A systematic process causes a change in gene frequency both
direction and amount.
D.S. Falconer listed the systematic processes as selection,
migration, and mutation.

Selection
 Selection is the most important process by which plant breeders alter
population gene frequencies.
 This change may be greater or lesser than the population
mean, depending on the trait of interest.
 For example, breeders aim for higher yield but may accept and select
less toxic chemical containing genotype
 For selection to succeed:
there must be phenotypic variation for the trait to allow differences
between genotypes to be observed
the phenotypic variation must be partly genetic.

Modes of selection
 There are 3 basic selection – stabilizing, disruptive & directional
 These selection operate by natural and artificial selection.
A key difference lies in the goal.
In natural selection, goal is to increase fitness of species,
In artificial, breeders impose selection to direct
population toward a specific goal

Stabilizing selection
 Selection for population mean & against either extreme expression of
phenotype
 E.g. selection will favor neither early flowering nor late flowering.
Disruptive selection
 mode of selection in which extreme variants have higher adaptive
value than those around the average mean value.
 It promotes diversity/ polymorphism.
Directional selection
 favor towards to one extreme phenotype & leads to establishment
of dominance
Plant breeders, impose directional selection to change existing
genotypes to targeted trait(s) to or optimal expression.
To achieve this, breeder employs techniques like crossing to
reorganize genes form parents in a new genetic matrix by
recombination

Effect of mating system on selection
 They may be grouped into two broad categories as random mating
and non-random mating (genetic assortative mating, phenotypic
assortative mating, and disassortative mating).
Random mating
 In plants, random mating occurs when each female gamete has an
equal chance of being fertilized by any male gamete of the same
plant or with any other plant of the population
 If the goal of breeder is to preserve desirable alleles random
mating will be an effective method of breeding.

Non-random mating
 Non-random mating has two basic forms:
assortative mating or inbreeding (Promote homozygosity):
If mating occurs between mating pair has the same phenotype
Used to develop homozygous lines (e.g., developing
inbred lines for hybrid seed breeding )
disassortative mating (promoting heterozygosity): If mating
occurs between non similar phenotype

Mating designs for random mating populations
 mating design is usually applied to schemes used by breeders and
geneticists to impose random mating for a specific purpose.
 To use these designs, certain assumptions are made by the breeder:
poloids nature of plant material diploid.
genes controlling the trait of interest are independently
distributed among the parents (i.e., uncorrelated gene
distribution).
 The absence of:
 non-allelic interactions,
reciprocal differences,
multiple alleles at the loci controlling the trait,
G x E interactions.

Types of Mating designs
 There are several types of mating designs to impose random mating
for a specific purpose.
A. Biparental mating (or pair crosses) (BIPs)
B. Polycross
C. North carolina design I (NCM-I)
D. North carolina design II (NCM-II)
E. North carolina design III (NCM-III)
F. Diallel cross
Comparative evaluation of mating designs
 scientist summarized these mating design into 2 ways:
1. In terms of coverage of the population: BIPs > NCM-I > Polycross
> NCM-III > NCM-II > diallel,
2. In terms of amount of information: Diallel>
NCM-II > NCM-II > NCM-I > BIPs.

Inbreeding
 Inbreeding is measured by the coefficient of inbreeding (F), which is
the probability of identity of alleles by ancestry.
 range of F is zero (no inbreeding) to one (prolonged selfing).
Inbreeding and its implications in plant breeding
 inbreeding provides opportunity for recessive alleles to be expressed.
 inbreeding has little or no adverse effect in inbred species,
 in cross-bred species has adverse effect when recessive alleles are
less favorable & create inbreeding depression
it reduces performance due to expression of deleterious alleles.
 severity of inbreeding depression varies among species, e.g alfalfa
inbreeding produces plants that fail to survive.
 Inbreeding is desirable in some breeding programs.
Inbred cultivars of self-pollinated species retain their genotype
through years of production.
In cross-pollinated species, inbred lines are deliberately
developed for use as parents in hybrid seed production.

population improvement
 goal of improving cross-pollinated species is to change gene
frequencies in population towards favorable alleles while
maintaining a high degree of heterozygosity.
Strategy for population improvement
 The population can be changed by one of two general strategies
by population improvement
changing population by applying specific selection tactic.
by development of synthetic cultivars.
open-pollinated cultivar developed from combining inbred
or clonal parental lines called synthetic cultivars.
However, cultivar is not sustainable and must be
reconstituted from parental stock.

II. quantitative genetics
 Most of the traits that plant breeders are interested in are
quantitatively inherited.
What is quantitative genetics?
 Population genetics and quantitative genetics are closely related fields
 Both dealing with genetic basis of phenotypic variation among
individuals in a population.
Population genetics focuses on frequencies of alleles &
genotypes
quantitative genetics focuses on linking phenotypic variation
of complex traits to its underlying genetic basis

II. quantitative genetics…
 quantitative genetics focuses on the use of molecular genetics tools
(genomics, bioinformatics, transcrpitomics, etc.) to reveal links b/n genes
& complex phenotypes
 Genes control quantitative traits called quantitative trait loci (QTLs).
 Molecular-based QTL analyses are being used to evaluate:
 the link associations of polymorphic DNA sites with phenotypic
variations of quantitative & complex traits
 analyzing polymorphic DNA genetic architecture.
 quantitative genetics may be grouped as
classical quantitative genetics: deals with study of passage of
QTLs from one generation to next through breeding experiments
in individual organism
molecular quantitative genetics: evaluating link association of
polymorphic DNA sites with phenotypic variations of
quantitativetraits

Qualitative genetics versus quantitative genetics
 They mainly differ as follows:
Nature of traits
Qualitative genetics is concerned with traits that have
Mendelian inheritance and can be described according to kind
and, can be unambiguously categorized.
Quantitative genetic traits are described in terms of the degree
of expression of the trait, rather than the kind
 Scale of variability
Qualitative genetic traits provide discontinuous phenotypic
variation,
quantitative genetic traits produce continuous phenotypic
variation
Number of genes.
 In qualitative genetics, the effects of single genes are readily
detectable,
in quantitative genetics single gene effects are not discernible
(small indistinguishable effects).

Qualitative genetics versus quantitative genetics…
 Mating pattern.
 Qualitative genetics is concerned with individual matings and
their progenies.
 Quantitative genetics is concerned with a population of
individuals that may comprise of a diversity of mating kinds.
 Statistical analysis.
 Qualitative genetic analysis is quite straight forward; it is based
on counts and ratios.
 quantitative analysis provides estimates of population
parameters (using sample).

Quantitative trait & qualitative trait
Most traits encountered in plant are quantitatively inherited.
Many genes control such traits,
 each contributing a small effect to the overall phenotypic
expression of a trait.
Variation in quantitative trait expression is continuous.
The traits that exhibit continuous variations are also called
metric traits.
Any attempt to classify such traits into distinct groups is only
arbitrary.
For example, height is a quantitative trait.
 If plants are grouped into tall versus short plants,
relatively tall plants could be found in the short group
and vice versa

Gene action on quantitative trait
 There are four basic types of gene action: additive, dominance,
epistasis, and overdominance.
 Because gene effects do not always fall into clear-cut categories,
quantitative traits are governed by genes with small individual
effects,
 they are often described by their gene action rather than by the
number of genes by which they are encoded.
 It should be pointed out that gene action is conceptually the same for
major genes as well as minor genes,

Additive gene action
 The effect of a gene is said to be additive when each additional gene
enhances the expression of the trait by equal increments.
 Consequently, if one gene adds one unit to a trait, the effect of aabb
=0, Aabb =1, AABb =3, and AABB =4.
 In the case of a single locus (A, a) the heterozygote would be exactly
intermediate between the parents (i.e., AA =2, Aa 1, aa =0).

Dominance gene action
 Dominance action describes the relationship of alleles at the same
locus.
 When dominance is complete, the heterozygote is equal to the
homozygote in effects (i.e., Aa = AA).
The breeding implication is that the breeder cannot distinguish
between the heterozygous and homozygous phenotypes.
Consequently, both kinds of plants will be selected, the
homozygotes breeding true while the heterozygotes will not
breed true in the next generation
 (i.e., fixing superior genes will be less effective with
dominance gene action).

Overdominance gene action
 Overdominance gene action exists when each allele at a locus
produces a separate effect on the phenotype and their combined
effect exceeds the independent effect of the alleles.
 From the breeding standpoint, the breeder can fix overdominance
effects only in the first generation (i.e., F1 hybrid cultivars)

Epistatic gene action
 Epistasis is the interaction of alleles at different loci.
 It complicates gene action in that value of a genotype or allele at one
locus depends on genotype at other epistatically interacting loci.
the allelic effects at one locus depend on the genotype at a
second locus.
 An effect of epistasis is that an allele may be considered “favorable”
at one locus and then considered “unfavorable” under a different
genetic background.
 Epistasis is sometimes described as the masking effect of the
expression of one gene by another at a different locus.

Gene action and plant breeding
 Understanding gene action is critical to success of plant breeding.
 It is used by breeders several ways:
in the selection of parents used in crosses to create segregating
populations in which selection is practiced;
in choice of the method of breeding used in crop improvement;
in research applications to gain understanding of the breeding
material by estimating genetic parameters.

Variance components of a quantitative trait
 The genetics of a quantitative trait centers on study of its variation.
 As D.S Falconer stated, it is in terms of variation that the primary
genetic questions are formulated.
 K. Mather expressed the phenotypic value of quantitative traits in
this commonly used expression:

Heritability
What is heritability?
 Heritability is the ratio of genetically caused variation to total
variation (including both environmental and genetic variation).
Estimates of heritability
 is Heritability may be estimates using the total genetic variance
(VG) is called broad sense heritability.
 It is expressed mathematically as:
 H = VG/VP
Factors affecting heritability estimates
 The magnitude of heritability estimates depends on the
 genetic population used,
sample size,
the method of estimation.

Chapter 3: Plant Reproductive systems
 Plant reproduction and autogamy
 Auto & Allogamy
Hybridization
Clonal propagation and in vitro culture

Plant reproduction and autogamy
 Plant Reproduction is process of plants multiply themselves.
 mode of reproduction determines method of breeding
Importance of mode of reproduction to plant breeding
 Why plant breeders need to know mode of plant reproduction
I. Since genetic structure depend on mode of reproduction to
understand the genetic structure
II. to perform artificial hybridization
III. to apply Pollination control mechanism
IV. To determines procedures for multiplication & maintenance of
cultivars.

Reproductive options in plants
 There are 4 broad & contrasting pairs of reproductive mechanisms
I. Hermaphrodity versus unisexuality.
II. Self-pollination versus cross-pollination.
(iii) Self-fertilization versus cross-fertilization.
IV. Sexuality versus asexuality.

Sexuality versus asexuality
A. Sexually reproducing plants
produce seed as the primary propagule.
Seed is produced after sexual union of gametes.
Gametes are products of meiosis so seeds are genetically
variable.
B. Asexual or vegetative reproduction mode
use any vegetative part of the plant for propagation.
Asexual reproduction is also applied to the condition whereby
seed is produced without fusion of gametes (called apomixis).

Sexual lifecycle of a plant (alternation of generation)
 A flowering plant goes through two basic growth phases
vegetative phase,
plant produces vegetative growth only (stem, branches etc.).
reproductive phase
 flowers are produced.
 In some species environmental factor like temperature, photoperiod
is required to switch from the vegetative to the reproductive phase.

Sexual reproduction process
 Two processes must occur in sexually reproducing species.
 first process, meiosis, diploid (2n) goes to haploid (n)
second process, fertilization, unites nuclei of two gametes,
 In higher plants male gametophyte generation is reduced to a tiny
pollen tube & three haploid nuclei (called the microgametophyte).
 The female gametophyte (called the megagametophyte) is a single
multinucleated cell, also called the embryo sac.

Duration of plant growth cycles
 plant breeder should know lifecycle of plant b/se breeding
influenced by duration of plant growth cycle.
 Angiosperms (flowering plants) may be classified into four
categories based on the duration of their growth cycle
i) Annual.
 Complete their lifecycle in one growing season.
Examples of such plants include corn, wheat, and sorghum.
ii) Biennials.
 completes their lifecycle in two growing seasons.
 In first season basal roots, stem and leaves produce
 in second season flowers, fruits & seed, produce plant.
 These plant may requires a special environmental condition
(e.g., vernalization) to be induced to enter reproductive phase.

(iii) Perennial
 have ability to repeat their lifecycles indefinitely by avoiding
death stage and need 5 to 10 years to change their growth stage
 They may be underground rhizomes, aboveground stolons & woody
like fruit crop
(iv) Monocarps
 They are annuals or biennials, but some persist in vegetative
development for very long periods before they flower and set seed
 Once flowering occurs, the plant dies. (e.g., bamboo).
That is, monocarps are plants that flower only once.
 top part may dies & new plants arise from root system of old plant.

The flower structure
 In breeding the technique of crossing needs flowers.
 To be successful, the plant breeder should be familiar with the
flower structure.
 Flower structure affects the way of flower emasculation
 The size of the flower affects the kinds of tools and techniques that
can be used for crossing.
Morphology of flower
 Four major parts of flower are: petal, sepal, stamen & pistil.
stamen: Male part of flower
Pistil: female part of flower
Sepal: leaf-like structures that enclose
the flower
Petal: showiest parts of the flower

Types of flowers
 Complete flower: has all four major parts
 incomplete flower: lacks certain parts (often petals or sepals),
 perfect flower (bisexual): both stamens & pistil in same flower
 It may be monoecious plant like corn
 imperfect flower: flowers is either stamens or pistil
 If imperfect flowers have stamens are called staminate flowers.
 When only a pistil occurs, the flower is a pistilate flower.
 E.g papaya plant said to be dioecious plants.
 Flowers may either singly or an inflorescence.
 So, it is clear plant breeder know specific characteristics of
flower select appropriate techniques for crossing.

Gametogenesis
 Sexual reproduction entails gametes

Pollination and fertilization
 Pollination is transfer of pollen grains from anther to stigma
 This transfer is achieved through a vector or pollination agent.
 common pollination vectors are wind, insect, mammals, and birds.
 When compatible pollen falls on a receptive stigma, a pollen tube
grows down style to micropylar
 tube penetrates sac through the micropyle.
 One of sperms unites with the egg cell, a process called fertilization.
 On basis of pollination mechanisms, plants grouped into two
Self pollinated or cross-pollinated.
Self-pollinated species accept pollen primarily from the anthers of
the same flower (autogamy).
The flowers, must be bisexual.
 Cross-pollinated species accept pollen from different sources.

Autogamy prevention& ensuring mechanism
 Certain natural mechanisms ensure self-pollination,
Cleistogamy is the condition in which the flower fails to open
(flower opens only after it has been pollinated)
stigma of the flower is closely surrounded by anthers, making it
prone to selfing.
 mechanisms prevent self-pollination (e.g., selfincompatibility via
several reasons , male sterility, Dichogamy: the maturing of pistils
and stamens of a flower at different times).

Plant breeding implications of self-incompatibility
 Self-incompatibility promotes heterozygosity.
 selfing selfincompatible plants can create significant variability from
which a breeder can select superior recombinants.
Self-incompatibility may be used in plant breeding (for F1
hybrids, synthetics, triploids), but first homozygous lines must
be developed.

Allogamy
What is allogamy?
 Allogamy occurs when fertilization of the flower of a plant is effected
by pollen donated by a different plant within the same species.
 This is synonymous with cross-pollination, cross-fertilization or
outbreeding

Examples of predominantly cross-pollinated species.

Mechanisms that favor allogamy
 allogamy commonly have taller stamens to better ensure the dispersal
of pollen to other plants flowers.
 timing of the receptiveness of the stigma and shedding of pollen
and, thereby prevent autogamy within the same flower
Protandry flower: anthers release pollen before stigma of the
same flower is receptive
protogyny flower: stigma is receptive before the pollen is shed
from the anthers of the same flower.
 Several mechanisms occur in nature by which cross-pollination is
ensured, the most effective are:
 dioecy: sexes occur on different plants
Monoecy: sexes occur in different locations on same plant
Dichogamy: maturing of pistils and stamens of a flower at
different times.
 selfincompatibility

Breeding implications of allogamy
 increase heterozygous because of lack of restriction on pollination.
 open-pollinated cultivars are less stable, changing genetic identity of
all constituting plants from one generation to next.
 From generation to generation certain genes may be selected
against or for, changing the allele frequencies.
For example, after a cold period plants with low frost tolerance
may die, while plants possessing one or more alleles for cold
tolerance will have normal reproduction.
Such an event will cause an increased allele frequency for
frost tolerance.

Hybridization
Gene transfer and hybridization
 In flowering species gene transfer or gene combination is by crossing
or sexual hybridization.
 The product of hybridization is called a hybrid.
 Sexual hybridization can occur naturally through agents of
pollination.
 Artificial hybridization is common conventional breeding to
generating a segregating population for selection
 tools of modern biotechnology now enable the breeder to transfer
genes by circumventing the sexual process (i.e., without crossing).

Applications of crossing in plant breeding
 crossing is done for specific purposes, within the general framework
of generating variability. These are :.
 Gene transfer:
Recombination.
 Break undesirable linkages.
For heterosis..
 For maintenance of parental lines. E.g hybrid seed development
programs,
 For maintenance of diversity in a gene pool.
For evaluation of parental lines
For genetic analysis

Artificial hybridization
 Artificial hybridization is deliberate crossing of selected parents
 There are specific methods on crossing depend on species but certain
basic factors to consider in preparation for hybridization:
Parents should belong to same or closely related plant species.
parents should supply critical genes to the breeding objective
select one parent to be a female and the other a male
The female parent usually needs some special preparation like
removing the anthers ( emasculation)
Transfer pollen physically or manually

Artificial pollination control techniques
(i) Mechanical control
 This approach entails manually removing anthers from bisexual
flowers
(ii) Chemical control
 A variety of chemicals called chemical hybridizing agents ( male
gametocides, male sterilants, pollenocides, androcides) are used to
temporally induce male sterility in some species.
iii) Genetically control
 Certain genes are known to impose constraints on sexual biology by
incapacitating the sexual organ or inhibiting the union of normal

Flower and flowering issues in hybridization
 The success of a crossing program depends on the condition of the
flower regarding
 overall health,
 readiness or receptiveness to pollination or exact flowering
time or Synchronization of flowering
Maturity etc

Clonal propagation and in vitro culture
What is a clone?
 In biology, a clone is an organism whose genetic information is
identical to that of parent from which it was created.
 In plants, a clone means a genetically uniform plant material
derived from a single individual and propagated exclusively by
vegetative (non-seed) methods.
 This may occur through
modified underground
sub-acrial stems, and
through bulbills

Clones, inbred lines, and pure lines
 The terms pure line, inbred line, and clone are applied to materials
developed by plant breeders
 Pure lines: genotypes developed as cultivars of self-pollinated
crops for direct use by farmers.
 Inbred lines: genotypes that are developed to be used as parents in
the production of hybrid cultivars and synthetic cultivars in the
breeding of cross-pollinated species.
 Clones: Clones are identical copies of a genotype

Categories of clonally propagated species for breeding purposes
 For breeding purposes they grouped into four
 normal flowering and seed set
 They produce normal flowers and are capable of sexual
reproduction without artificial intervention (e.g., sugar cane).
 normal flowers but have poor seed set
 produce normal looking flowers that have poor seed set, or set seed
only under certain conditions but not under others.
 Produce seed by apomixis.
 The phenomenon of apomixis results in the production of seed
without fertilization,
 Over 100 species of perennial grasses have this reproductive
mechanism.
 Non-flowering species.
 These species may be described as “obligate asexually
propagated species” because they have no other choice.

Significance of Vegetative Reproduction
 Vegetative reproducing species offer unique possibilities in breeding.
A desirable plant may be used as a variety directly regardless of
whether it is homozygous or heterozygous.
 mutant buds, branches or seedlings, if desirable, can be
multiplied and directly used as varieties.

In vitro culture
 In vitro culture is used as a technique by plant breeders
 It is critical in modern plant breeding approaches, in which genetic
alterations are conducted under aseptic conditions.
 Tissues and even single cells can be nurtured to develop into full
plant

Chapter 4 :Germplasm for breeding

Variation: types, origin & scale
 Classifying plants
Types of variation among plants

Plant domestication
Evolution
Center of origin & center of diversity

Plant genetic resources
Sources of germplasm for plant breeding
gene pools of cultivated crops
genetic vulnerability
Plant genetic resources conservation

Variation: types, origin & scale
Classifying plants
 Plant taxonomy is science of classifying & naming plants.
 Organisms are classified into five major groups
 Plant breeders directly concerned plant kingdom
 An international scientific body sets the rules for naming plants.
 Standardizing naming of plants eliminates confusion from
numerous culture-based names of plants.

E.g corn in the United States is called maize in Europe
 The binomial nomenclature was developed by Carolus Linnaeus and
uses two names based on genus & species,

Binomial name writing
 There are specific ways of writing binomial name:
It must be underlined or written in italics (being non-English).
genus name must start with upper case letter & species a lower
The term “species” is both singular & plural, may be shortened
to sp. or spp.
 letter ‘L’ indicates that Linnaeus first named the plant.
If revised later, the person responsible is identified after the ‘L’,
 for example, Glycine max L. Merr (for Merrill).
generic name may be abbreviated.
 Zea mays- Z. mays,
cultivar or variety name may be included in the binomial name.
 E.G.Solanum lycopersicum cv. “Big Red”, or S. lycopersicum
“Big Red”.
The cultivar (cv) name, however, is not written in italics.

Rules of classification of plants
 science of plant taxonomy is coordinated by International Board of
Plant Nomenclature, which makes the rules.
 The Latin language is used in naming plants.
 Sometimes, names given reflect specific plant attributes/ use
some name indicate color, e.g. alba (white) and aureum (golden);
others are sativus (cultivated), tuberosum (tuber bearing), and
officinalis (medicinal).
 The ending of a name is often characteristic of the taxon.
Class names often end in opsida (e.g. Magnoliopsida),
orders in ales (e.g. Rosales), and
families in aceae (e.g. Rosaceae).

Operational classification systems
 Crop plants may be classified for specific purposes,
a) Seasonal growth cycle.
On this basis, crop plants may be classified as annual, biennial,
perennial, or monocarp,
(b) Stem type.
 woody, non-woody stems, herbs (or herbaceous plants), Shrubs
(c) Agronomic use.
Cereals, Pulses, Grains, Forage, Roots &Tubers ,Oil crops, Fiber
crops ,Sugar crops ,Green manure crops , Cover crops
e) Adaptation.
Temperature adaptation as either cool or warm season plants.

Types of variation among plants
 phenotype (the observed trait) is the product of the genotype and the
environment (P = G + E).
 The phenotype may be altered by altering G, E, or both.
Environmental variation
 When identical genotypes are grown in field exhibit differences in
expression of some traits because of non-uniform environment.

field is often heterogeneous with respect to plant growth
factors; nutrients, moisture, light, and temperature
 plants that occur in more favorable parts of the field would perform
better than disadvantaged plants.

due to the environmental variation if breeder selects inferior
genotype by mistake, breeding program will be slowed.

Genetic variability heritable variation
 It is Variability that can be due to genes that encode specific traits &
can transmitted from one generation to next.
 since genes are expressed in environment, degree of expression
impacted by its environment
 Heritable variability is crucial to plant breeding.
 Heritable variability constantly expressed generation to generation.
 e.g purple-flowered genotype always produce purple flowers.
a mutation can permanently alter an original expression.
E.g, a purple-flowered plant may be altered by mutation to
become a white-flowered plant.

Origins of genetic variability
 There are 2 main ways in w/c genetic variability originates in nature;
sexual reproduction
 Crossing over (in prophase I),
Random assortment of chromosomes (in metaphase I),
Random fusion of gametes from different,
Mutation (both point & cheromosomal)
 plant breeders use a variety of techniques make these variation
source more targeted for their breeding programs.
With advances in science and technology (e.g., gene
transfer, somaclonal variation)
.

Scale of variability
 variability can be readily categorized by
 counting and placing into distinct nonoverlapping groups;
this is said to be discrete or qualitative variation.
Traits that exhibit this kind of variation are qualitative traits.
 Other kinds of variability occur on a continuum and cannot be
placed into discrete groups by counting
this is said to be nondiscreteor quantitative variation
 Traits that exhibit this kind of variation are quantitative traits.

Plant domestication
Evolution
 Evolution is a population phenomenon, not individuals, evolve.
 Evolution concerned changes in frequency of alleles in a population,
It leads genetic diversity and the ability of the population to
undergo evolutionary divergence.
 Darwin stated, variation is a feature of natural populations.
individuals with best genetic fitness for specific environment will
survive & reproduce more successfully :
 become more competitive than other individuals.
The discriminating force, called natural selection by
Darwin
 A key factor in evolution is time.

How breeder use the evolution to develop cultivar?
 When individuals form subpopulation & reproductively isolated
from the original population new species will eventually form.
Patterns of such evolutionary changes have been unconsciously
copied by plant breeders to development new cultivars.
Plant breeders have discarded unfavorable plant types from
favored to be represented in next plant generations.
This natural selection (like frost tolerance) supported by man-
guided selection
resulting in plant populations that better and better
fitted the needs of man.

What principle of natural selection are core of breeding?
(i) Variation
variation in morphology, physiology, and behavior exist among
individuals in a natural population.
(ii) Heredity
offspring resemble their parents more than they resemble unrelated
individuals.
(iii) Selection
some individuals in a group are more capable of surviving and
reproducing than others (i.e., more fit)

Domestication
What is domestication
 Domestication is the process genetic changes in wild plants by a
selection process imposed by humans for their benefit.
 It is also an evolutionary process in which selection (both natural &
artificial operation) applied to change plants:
genetically

Morphologically
physiologically
 The results of domestication are plants that are adapted to
supervised cultural conditions and by producers & consumers.

Centers of domestication or origin & center of diversity
 Plant breeders are interested in centers of plant
 the most important centers of domestication are also the regions
where farming started.
 Vavilov of Russia, on his plant explorations in the world in 1920s &
1930s, noticed extensive genetic variability within a species
 He summarized his observation
center of origin of a crop plant exhibits maximum diversity of
varieties & ancestral species occurs in that region in the wild
 centers of domestication are almost always also centers of diversity,
but the reverse is not true.
E.g. China is highest in diversity of waxy corn, which was
domesticated in Central America.

Changes associated domestication
 assortments of morphological & physiological traits modified in
domestication process is domestication syndrome by J.R. Harlan.
 exact composition of the domestication syndrome traits depends on
particular species, certain basic characteristics are common
Genetic bottleneck
 A notable characteristic of most domesticated plants is a reduction in
the genetic diversity due to the so called genetic bottleneck.

In the widely studied maize crop, diversity reduction between
teosinte and modern corn is about 30%.
Tempo/speed of domestication
 The conventional view of domestication had for a long time
 The recent time domestication syndrome is quick

the conscious or artificial selection pressure and its high
influence in modifying genetic patterns of diversity.

Plant genetic resources/ germplasm
What is germplasm?
 Germplasm is the lifeblood of plant breeding without which
breeding is impossible to conduct.
 It is genetic material that can be used to maintain a species or
population.
 Germplasm provides materials (parents) used to initiate a
breeding program.
 When breeders need to improve plants, they have to find a source of
germplasm

Sources of germplasm for plant breeding
 The major sources of germplasm for plant breeders may be
categorized into three broad groups:
1. domesticated plants,
2. undomesticated plants
3. other species or genera.

Domesticated plants
There are various types of such material (commercial cultivar,
breeding material, Landraces, Plant introductions & Genetic stock)
Commercial cultivars.
There are two forms of this material – current cultivars and
retired or obsolete cultivars.
These are products of formal plant breeding for specific
objectives.
If desirable parents are found in these cultivars, breeder
can use them for other objective.

 Breeding materials.
These are Ongoing or more established breeding programs
materials
Many of the genotypes have unique traits will be retained as
breeding materials to be considered in future projects.
Landraces.
 Landraces are farmer-developed and maintained cultivars.
They are developed over very long periods and have co-adapted
gene complexes.
They are adapted to the growing region and are often highly
heterogeneous.

Plant introductions.
 The plant breeder may import new, unadapted genotypes from
another country (called plant introductions).
 these may be evaluated and adapted to new production regions as
new cultivars, or used as parents for crossing in breeding projects.
Genetic stock.
 This consists of products of specialized genetic manipulations by
researchers
 (e.g., by using mutagenesis to generate various chromosomal
and genomic mutants).

Undomesticated plants
When desired genes are not found in domesticated cultivars,
breeders seek them from wild populations.
from wild type undesirable trait also will be transferred to
modern cultivation.
These undesirable traits have been selected against through the
process of domestication.
Other species and genera
These materials are from other species or genera via wide cross
Since wide crosses is less successful, often requiring special
techniques (e.g., embryo rescue)

gene pools of cultivated crops
J.R. Harlan categorized gene pools of cultivated crops according to
the feasibility of gene transfer or gene flow
3 categories were defined, primary, secondary, & tertiary gene
pools:
Harlan suggested that breeders first utilize the germplasm in the
GP1 and proceed outwards.
Crop gene
pools

genetic vulnerability
What is genetic vulnerability?
 Genetic vulnerability is a term used to indicate genetic homogeneity
and uniformity of a group of plants that predisposes to:
 pest, pathogen/ environmental hazard of large-scale
proportions.
A case in point is the 1970 epidemic of southern leaf blight in the
United States that devastated the corn industry.
This vulnerability was due to uniformity corn widespread use
of T-cytoplasm in corn hybrid seed production.

What plant breeders can do to address crop vulnerability?
1. Reality check
First, plant breeders need to understand genetic vulnerability is a
real and present danger.
2. Use of wild germplasm
Many of the world’s major crops are grown extensively outside
the centers of origin where they co-evolved with pests and
pathogens.
Breeders should exploit genes from wild progenitors of their
species that are available in all over the world.

3. Paradigm shift
 The researchers proposed a shift from the old paradigm of looking for
phenotypes to a new paradigm of looking for genes.
the modern techniques of genomic used to screen germplasm by
a gene-based approach.
the use of molecular linkage maps and a new breeding technique
called advanced backcross QTL introgression
4. Use of biotechnology to create new variability
Biotechnological tools like recombinant DNA, cell fusion,
somaclonal variation, Genetic engineering etc
5. Gene pyramiding
It is introducing more than one resistance gene into one genotype.

Plant genetic resources conservation
 breeding programs narrowed overall genetic base of modern
cultivars
Why conserve plant genetic resources?
There are several reasons:
 Plant germplasm is exploited for d/t purposes (food, fiber etc)
 As a natural resource, germplasm is a depletable resource.
 Without genetic diversity, plant breeding cannot be conducted
 Genetic diversity determines crop productivity and survival.
 To cater for future needs.

Genetic erosion
 It is the decline in genetic variation in cultivated/ natural populations
 It may be caused by natural or human factors
1. Natural factors.
 it includes natural disasters (large-scale floods, wild fires,
prolonged drought etc).
2. Human factor
This factor include several mechanism of human action
Action of crop producers.
Action of breeders.
problems with germplasm conservation
General public action

Approaches to germplasm conservation
 There are 2 basic approaches (in situ and ex situ).
1. In situ conservation
It is the preservation of variability in its natural habitat (i.e., on site).
More applicable to wild plants
These protected areas are called by various names (e.g., nature
reserves, wildlife refuges, natural parks)
2. Ex situ conservation
It is the preservation out of their natural places of origin
 it needs supervision of professionals
 the site or locations is called gene banks.

Germplasm collection
Planned collections conducted by experts to regions of crop origin.
These trips are often multidisciplinary expertise in botany, ecology,
pathology, population genetics, and plant breeding.
Familiarity with the species of interest and the culture of the regions
to be explored are advantageous.
 Most of the materials collected are: seeds, vegetative parts (e.g.,
bulbs, tubers, cuttings, etc.) and pollen may be collected.

Seed material viability
 Based on viability, seed may be classified into two main groups –
orthodox and recalcitrant seed.
(i) Orthodox seeds.
These can prolong their viability under reduced moisture content
and low temperature in storage.
 E.g include cereals, pulses, and oil seed like rape.
(ii) Recalcitrant seeds.
Low temperature and decreased moisture content are intolerable
to these seeds (e.g., coconut, coffee, cocoa).
In vitro techniques might be beneficial to these species for long-
term maintenance.

Types of plant germplasm collections
 Germplasm is stored in four categories:(base collections, backup
collections, active collections & breeders’ or working collection.
 These categorizations are only approximate since one group can
fulfill multiple functions.
Base collections
These are not intended for distribution to researchers, but are
maintained in long-term storage systems.
Storage conditions are low humidity at freezing temperatures (-
10 to-20 oC) or cryogenic (-150 to -195 0C), depending on the
species.
Materials can stored for many decades under proper conditions.

Backup collections
This collections is to supplement the base selection.
In case of a disaster at a center act as duplicate collection
This provide an insurance against the loss of seed in the event of a
large scale catastrophic regional or global crisis.
Active collections
the materials in active collections are available for distribution to
plant breeders or other patrons upon request.
Working or breeders’ collections
It is primarily composed of elite germplasm that is adapted.
 They include enhanced breeding stocks & recombinant DNA
(rDNA) with unique alleles for introgression into adapted plants.

Germplasm storage technologies
Once collected, germplasm is maintained in the most appropriate
form by the gene bank with different storage technologies.
Seed storage
Field growing
Cryopreservation
In vitro storage
Molecular conservation

International conservation efforts
germplasm transactions need international cooperation for success.
No one country is self-sufficient in its germplasm needs.
Most of the diversity resides in tropical and subtropical regions of
the world where most developing nations occur.
These germplasm-rich nations, unfortunately, lack the resources and
the technology to make the most use of this diversity

Who owns biodiversity?
Biodiversity is sum of genetic differences existing in living
organisms at molecular, individual, population & ecosystem
levels.
It is crucial to the development of new and improved cultivars.
ownership of biodiversity became more important beginning in the
1970s, partly for political as well as economic reasons.
Prior to that time, biodiversity was treated as common property to
humankind (common heritage
it is know pointed out that biodiversity resides within the borders
of sovereign nations.
access to biodiversity is not without restrictions.
oE.g the governments of Peru and Bolivia restrict the
export of planting materials of quinine

Chapter 5: Breeding objectives
Yield and morphological traits
Quality traits
 Breeding for resistance to diseases and insect pests
Breeding for resistance to abiotic stresses

Yield and morphological traits
 what is the first step of plant breeding?
Yield trait
 Plant growth depend on interaction of biochemical & physiological
processes.
 These processes influenced by both genetic & environment.
 major physiological processes are:
 photosynthesis
respiration
translocation and transpiration
So, Crop yield depend on the processes of these
quantitatively inherited traits

What is yield?
 Yield is general term describe amount of crop that is harvested from
a given area at harvesting season.
 Yield may be grouped as biological and economical
Biological yield
 total dry matter produced per plant or per unit area (i.e.,
biomass).
 All yield is firstly biological yield.
Economic yield
 total weight per unit area of a specified plant product that is of
marketable value or other use to the producer.

Ideotype/ idealized appearance of a plant variety
 breeders may be associated to plant structural for high yield.
 Certain plant organs have the capacity to act as:
 sinks (importers of substrates) &
 sources (exporters of substrates).
But organ can be source for one substrate & sink to another.
E.g. leaves are sinks for nutrients absorbed from soil while they
serve as sources for newly formed a.a
 Plant genotypes differ in patterns for partitioning.
So, breeders can influence dry matter partitioning.

Improving the efficiency of dry matter partitioning
 harvest index is the proportion of the plant that is of economic value.
 It is calculated as a ratio as follows:
 Harvest index use as a selection criterion for yield
yield potential
 It is crop inherent optimum capacity to perform under a given
environment.
 only 20–40% of this yield potential can be attained economically in
actual production on farmers’ fields. Why?

yield plateau
 Even though global total crop yields are continually rising, the rate of
yield growth is slowing.
This trend is termed yield stagnation or yield plateau,
 e.g. yield growth rates for wheat declined from 2.92% (between
1961 and1979) to 1.78% (between 1980 and 1997).
Yield stability
 Breeder is not only interested to develop high yielder cultivars.
interested in developing cultivars with sustained/ stable high
performance over seasons and years (yield stability).

Morphological trait
 It is general aspects of visible biological form & arrangement of
plant parts
 There are several types of morphological traits related with
breeder objectives
Lodging resistance
Shattering resistance
Reduced plant height
Breeding determinacy
Photoperiod response
Early maturity

Lodging resistance
 Lodging resistance may be defined as the leaning, bending, or
breaking of the plant prior to harvesting.
Nature, types, and economic importance of lodging
 There are two basic types of lodging that may be caused by biotic or
abiotic factors.
 Lodging may originate at the root level (root lodging) or at the
stem or stalk level (stalk lodging).

Genetics and breeding of lodging resistance
 Breeding for lodging resistance is challenging, because:
 it is a quantitative trait,
 its expression is significantly impacted by the environment.
 It may occur at different stages in plant growth, or never at all.
 However, resistance to lodging may be improved by targeting a
combination of the following traits (depending on species)
 short stature
stronger stalk
 strong stem
thick outer layer
strong root system
resistance to stalk or stem biotic factors

Shattering resistance
 Dry fruits that split open upon maturity to discharge their seeds are
called dehiscent fruits.
 it is undesirable in modern crop production
Nature, types, and economic importance
 fruits split along only one side (called a follicle), (beans, peas)
 split along two sides (called a legume), e.g. nuts
 multiple sides (called a capsule) e.g Cotton
 the splitting of dry fruits to release their seeds prior to harvesting is
called grain shattering.
 some cultivars can lose over 90% of their seed to shattering, if
harvesting is delayed by just a few days.

Breeding grain shattering resistance
 grain shattering resistance is also a complex trait.
 There is a large variation in the degree of shattering in plant genotype.
researchers have identified d/t genes that condition shattering
e.g. in rice, including sh1, sh2, sh4.

Reduced plant height
 Modern production of crops is dominated by semidwarf or dwarf
cultivars (e.g., rice, wheat, sorghum).
 plant height is associated with lodging resistance.
 Cultivars are environmentally more responsive & responding to
agronomic inputs.
 e.g. fertilizers, for increased productivity.

Breeding determinacy
 Plant growth form may be indeterminate or determinate.
 Some species, like corn and wheat, are determinate in growth
 soybeans have both determinate and indeterminate types.
• In indeterminate cultivars, new leaves continue to be initiated
even after flowering has begun.

Photoperiod response
 Photoperiodism is a photomorphogenic responsive to day length
 There are three categories of responses :
(i) Long-day (short-night) plants.
(ii) Short-day (long-night) plants.
(iii) Day-neutral (photoperiod insensitive).
Nature and economic importance
 It affects photosynthate partitioning in some species
 Decreasing partitioning to grain favors partitioning to vegetative
parts of the plant,
 resulting in increased leaf area & dry matter production.
 Crop cultivars that are developed for high altitudes should mature
before the arrival of winter, why?

Early maturity
 Crop maturity can be affected by a variety of factors in production
environment, including:
photoperiod,
temperature,
altitude,
moisture,
 soil fertility,
and plant genotype.
 Early maturity used to address some environmental stresses in crop
production, such as drought & temperature.
 Maturity impacts both crop yield and product quality.
 premature harvesting produces product quality for premium
prices.

Nature, types, economic importance
 There are two basic types of maturity
 physiological and
 harvest (market) maturity.
Physiological maturity
 It is stage at which plant cannot benefit from additional production
inputs (i.e. fertilizer, irrigation etc.)
because it has attained its maximum dry matter.
harvest (market) maturity
 In certain crops, the product is harvested before physiological
maturity to meet market demands.
 This stage of maturity is called harvest maturity.
E.g, green beans are harvested before physiological maturity to
avoid the product becoming “stringy” or fibrous.

Quality trait
 Quality means different things to different people.
The terms used to describe quality vary from crop production
to food consumption and
 it include terms for
appearance
storage quality
processing quality
nutritional quality.
Quality is highly crop specific. E.g.
milling quality and baking quality of wheat,
chipping or baking quality of potatoes,
malting quality of barley
fermenting quality of grapes.
 breeders should be very familiar with market quality standards
for their crops.
 b/se, these standards, highly crop specific.

Nutritional quality of food crops
 cultivars of the same species may differ significantly in total protein
as well as the nutritional value of the protein.
 The a.a profiles of cereal grains and legumes differ according to
certain patterns.
 Rice averages about 8% protein, corn 10%, potato 2%, versus 38–
42% in soybean, and 26% in peanut.
So. Protein augmentation /increase is a major breeding
objective in many major world crops.

Breeding seedlessness
 Fresh fruits without seeds are more convenient to eat, because there
are no seeds to spit out.
 Common fresh fruits in which seedless cultivars exist include
watermelon, grape, orange, and strawberry.

Breeding for resistance to diseases & insect pests
Selected definitions related to this topic
 Pest: An organism that is damaging to a crop & it includes plant
pathogenic fungi, bacteria, viruses, insects, and mammals.
 Parasite: An organism that feeds, grows, and is sheltered on or in a
different organism with out any contribution to the host
 Pathogen: An agent ( bacteria, viruses, fungi) that causes disease.
 Disease: Any condition caused by the presence of an invading
organism or a toxic component that damages the host.
 Pathogenecity. The ability of an organism to enter a host and cause
disease.
 Virulence. The degree of pathogenecity (the comparative ability to
cause disease)

 Infection: The invasion/attack & multiplication of a pathogenic
mircrooganism bodily part ; may lead to tissue injury and disease.
 Resistance: A response to a cause
 Immune: when genotype shows completely or totally resistant to
pathogen, (not showing any sign of infection).
 Host resistance: ability of specific plant species to resist specific
insects & pathogens b/se of a certain genetic architecture in the
plant.
 Non-host resistance: it is general phenomenon of immunity against
the majority of pathogens.

Groups of pathogens and pests targeted by plant breeders
 These pathogens may be airborne or soil borne.
Biological & economic effects of plant pathogens and pests
 There are several basic ways by which diseases & pests adversely
affect plant yield. They include the following:
Complete plant death
Partial plant death
Stunted growth
Vegetative destruction.
Direct product damage
Other effects

Methods for control of plant pathogens and pests
 Crop producers use variety of pathogen and pest control methods:
Quarantine
Phytosanitation and Cultural Practices
Application of pesticides
Biological control
Improvement of host resistance

Disease Resistance Mechanism of plant
 nature of mechanism may be biochemical, physiological, anatomical
or morphological.
 Resistance is a relative term for the genetic-based capacity of a host
to reduce the adverse effect of a pathogenic attack.
 It does not necessarily imply complete blocking of infection.
 host resistance mechanisms may be constitutive/ passive resistance
or induced / activated
constitutive/ passive
 Just because of the presence of various chemicals or any other
(e.g., catechol) in its outer scales.
induced / activated
 several genes/chemicals activate upon the attachment of the
pathogen exit

 In case of induce, infection-induced defense reactions are d/t
 hypersensitive
 overdevelopment of tissue
 underdevelopment
Hypersensitive reaction
 infection induces a rapid localized reaction,
 cells immediately surrounding point of attack die so that the
infection is restricted.
 pathogen eventually dies, leaving a necrotic spot (necrosis).
Overdevelopment of tissue
 Meristematic activity may be stimulated, resulting in disease free
tissue growth
 In some cases, a layer of suberized cells forms around invaded
tissue to limit the spread of the pathogen.
Underdevelopment of tissue
 plants become stunted in growth or organs become only partially
developed.

Types of genetic host resistance
 based on several associated criteria host resistance is generally
categorized into two major kinds: vertical or horizontal.
Vertical resistance
 it is race- or pathotype-specific in its effect,
 its inheritance is based on major genes resistance, and
 its effect in agricultural applications is usually not durable
Horizontal Resistance
 It is mostly controlled by polygenes and called minor gene
resistance.
 It Is considered to be durably effective

Biotic stress Resistance breeding strategies
 breeders have developed certain strategies
 first step in breeding resistance to pathogens is assemble and
maintain sources of resistance genes.
 resistant breeding needs :
Planned deployment of resistance genes
Gene pyramiding
Multilines
host population that is heterogeneous for resistance
genes
 it provides a buffering system against destruction
from diseases.

Challenges of breeding for pest resistance
 A major problem is when the crop cultural environment changes as
well as pathogen and pest (through evolution).
So, Breeders need to keep up the developing new cultivars with
appropriate resistance genes to ensure stability of production
Tolerance
 It is measured in terms of economic yield,
 it is not applicable to pathogens or insect pests that directly attack the
economic part of the plant (e.g., grain, tuber or fruit).
 it may be applied to a situation in which a plant recovers quickly
following a pest attack, such as grazing by a mammal.
 From the point of view of virologists, plants with little or no
symptoms are described as tolerant.

Applications of biotech on biotic stress resistance breeding
 Hundreds of R-genes have been cloned in many more crops to
many more pathogen and pest species.
Engineering insect resistance
 There are two basic approaches to genetic engineering of insect
resistance in plants:
(i) The use of protein toxins of bacterial origin.
(ii) The use of insecticidal proteins of plant origin.

Breeding for resistance to abiotic stresses
Types of abiotic environmental stresses
 Any stress environment may adversely impact plant growth
 common stresses abiotic stress include:
 Drought: perceived by plant as a consequence of water deficit.
 Heat: occurs when To are high enough damage in plant function.
 Cold: expose to low To that cause physiological disruptions
 Salinity: when the dissolved salts accumulate in the soil solution to
an extent that plant growth is inhibited.
 Mineral toxicity: when an element in the soil solution is present at a
concentration such that plants are physiologically impaired.

Drought stress
 It occurs above ground (atmospheric drought) or below ground (soil
drought).
 Its duration short time & without severe adverse impact, entire
growing season complete devastation of crops.
Breeding drought resistance
 Drought resistance is highly specific to crop region.
 Drought resistance is a major objective in dryland farming systems.
 to perform breeding drought resistance we considers several points:
Understand the principle
Characterizing the drought environment
Identifying Plant traits affecting drought response
Identify Mechanisms of drought resistance
Understand the principle
 breeder should understand nature of trait to be manipulated.
 Like developing genotype that had water-saving capacity.

Characterizing the drought environment
 Look its combination of physiological stress factors (rather than
one), even though one may predominate.
 E.g, drought may associated with low or high To,
 In irrigated production it is associated with salinity stress.
Identifying Plant traits affecting drought response
 Major traits play role in plant drought resistance response include:
 phenology (timing of vegetative activities, flowering, fruiting, and
their relationship to environmental factors),
 development and size
 root, plant surface
 non-senescence
 stem reserve utilization
 photosynthetic systems
 water use efficiency.

Identify Mechanisms of drought resistance
 Several general mechanisms:
 Escape (develop early maturing cultivars)
 Avoidance (avoid stress by decreasing water loss)
 Tolerance
 Recovery (

Salinity stress
 Salinity is the accumulation of dissolved salts in the soil solution to a
degree that it inhibits plant growth and development.
 Soils with salinity problems are described as salt affected.
 salt concentration measured in terms of electrical conductivity (ECe)
 when it is more than 4 dS/m (dissolved salts ) & the pH is less
than 8.5, the soil is called a saline soil.
 When the ECe value is less than 4 dS/m and the pH is more than
8.5, the soil is a sodic soil.
 Sodic soils are high in sodium (Na+) but low in other soluble salts.

Cause & consequence of salinity
 It may have natural origin (called primary salinity) as a result of
weathering of parent materials that are rich in soluble salts.
 Human-aided salinity (called secondary salinity) occurs by
agricultural activities like irrigation with salt-rich water.
 Plants that are tolerant to high soil salt concentration are called
halophytes.

Chapter 6 : Selection methods in plant breeding
Common plant breeding notations
 Selection &types of selection
Mass selection
Pure line selection
Pedigree selection
Bulk selection
Single seed descent selection
Clonal selection
Backcrossing
Types of cultivars

Common plant breeding notations
 breeders use standard genetic notations.
F(filial)
 It denotes the progeny of a cross between two parents.
 subscript (x) represents specific generation (Fx).
Selfing F2 plants produce F3 plants, and so on.
seed is one generation ahead of the plant, that is, F2 plant bears
F3 seed.

Notation pedigree and parent
 Some of the common notations are as follows:
A ‘/’ indicates a cross;
a figure between slashes, /2/, indicates order of crossing.
A/2/ is equivalent to//and indicates the second cross.
Similarly, /is the first cross, and///the third cross.
A backcross is indicated by *
Examples:
 Pedigree 1. MSU48-10/3/Pontiac/Laker/2/ MS-64. Interpretation:
1st cross was Pontiac (as female) x Laker (as male).
cross was [Pontiac/Laker (as female)] x MS-64 (as male)
 3rd cross was MSU48-10 (as F)x[Pontiac/Laker//MS-64 (as M)
 Pedigree 2. MK2-57*3/SV-2: Interpretation:
 genotype MK2-57 was backcrossed 3 times to genotype SV-2

SELECTION
 Once assembled or created varieties, breeders used selection
strategies to developed cultivars.
 Selection strategies may vary based on modes of reproduction
 It is isolation of desirable plant from population
 There are two agencies involved in carrying out selection:
Natural selection: for a long period it played more role
 artificial selection: plays important role in modern plant
breeding

Basic Principles of Selection:
 There are three basic principles of selection (Walker, 1969)
1. Selection operates on existing variability:
 it cannot create new variation.
2. Selection acts only through heritable differences:
Environmental variability cannot be of any use under selection.
3. Selection works when some individuals are favored in
reproduction at the expense of others :
These superior individuals are retained for reproduction while
others discarded under selection.
:

Selection intensity/strength :
 It is amount of selection applied expressed as proportion of the
population favored (selected).
 selection intensity is inversely proportional to percentage proportion
selected (PS)
Thus, larger the size of I, more stringent is the selection
pressure (hence low fraction is selected) and vice versa.

The progeny test
 It is evaluation of plants on basis of performance of their progenies
 The progeny test serves two valuable function;
1. Determines the breeding behaviour of a plant i.e. whether it is
homozygous or heterozygous.
2. Whether the character for which the plant was selected is
heritable i.e. is due to genotype or not.

Types of selection in plant breeding
1. Mass selection
 It is an example of selection variable population in genetic origin.
 in 1903 Danish biologist, W. Johansen, developed it
 described as oldest method of selection but still useful,
 Its purpose is population improvement by increasing gene
frequencies of desirable genes.
 Selection is based on plant phenotype
 Mass selection is imposed once or recurrent mass selection.
 cultivar development is by improving average performance of base
population.

Plant Breeding Full PPT (secA)This is course material for plant breeding..pdf

Plant Breeding Full PPT (secA)This is course material for plant breeding..pdf

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