Hybridization is the crossing of two plants to combine their genotypes. The objectives include combination breeding to transfer traits, transgressive breeding to create variations beyond parental limits, and producing hybrids with hybrid vigor. The process involves selecting parents, emasculating the female parent, bagging, tagging, pollinating, harvesting F1 seeds, and further handling plants. Polyploid breeding uses variations in chromosome number like polyploidy to induce trait changes. Haploids are useful for developing pure lines and aneuploids through chromosome doubling.

1. PRINCIPLES OF CROP PRODUCTION
ABT-320
(3 CREDIT HOURS)
LECTURE 04
PLANT HYBRIDIZATION
POLYPLOID BREEDING

2. PLANT HYBRIDIZATION
Genotype peculiarities of two or more different varieties or species of
plants could be brought together only by crossing them. The mating or
crossing of two plants or lines of dissimilar genotype is called
hybridization. In plant hybridization, one of the plants is taken as the
female plant and the other as the male plant. Pollen grains from the
male parent are made to pollinate the stigma of the flowers of the
female parent. The seeds obtained from such a cross are called F1 seeds
and the progeny raised from it is called F1 (First Filial) generation. The F1
is selfed to produce F2 and the subsequent generations like F3, F4 etc are
raised in the same way. These generations are called segregating
generations and they are handled differently based on the scope and
objectives of the breeding program.

3. OBJECTIVES OF HYBRIDIZATION
The major objectives of hybridization are:
A. Combination Breeding
Combination breeding is the transfer of one or more characters from other
varieties to a particular variety. These characters may be oligogenic or
polygenic. In this way, genes for disease resistance, quality traits etc can be
transferred.
B. Transgressive Breeding
Transgressive breeding is based on transgressive variation of characters in
segregating generations like F2. A cross is made between two strains of plants
and the F2 is screened for transgressive variations.
Transgressive segregation is the segregation of characters beyond the parental
limits, in the segregating generations like F2.
C. Production of Hybrids
Hybrid (F1) plants show higher vigor and yield when compared to parents, in
some cases. This phenomenon is called hybrid vigor. F1 seeds can be raised in
bulk through hybridization and distributed directly for cultivation, especially in
cross-pollinating crops.

4. TYPES OF HYBRIDIZATION
Based on the genetic difference between parents, hybridization can be
classified into:
1. Inter-varietal Hybridization
2. Distant Hybridization

5. INTER-VARIETAL HYBRIDIZATION
The cross between the members of the same species (intra-specific) is
called inter-varietal hybridization. In this type of hybridization, different
cross patterns can be used.
1. Simple Cross
In this case, two parents are used to produce an F1 hybrid.
2. Complex Crosses
In complex crosses, more than two parents are involved. Such
crosses can be called convergent crosses since they bring genes
from different sources together.

6. DISTANT HYBRIDIZATION
• Hybridization between the members of different species or hybridization
beyond species level is called distant hybridization. Thus, it may be
interspecific (intra-generic) or inter-generic. When conventional methods
of hybridization fails, para-sexual methods are used in such cases.
• Para-sexual hybridization is the technique of fusing somatic protoplasts
when reproductive cells fail to fuse or fertilize.

7. THE PROCESS OF HYBRIDIZATION
The major steps involved in the process of hybridization are:
1. Selection of Parents
2. Emasculation
3. Bagging
4. Tagging
5. Pollination
6. Harvesting F1 Seeds
7. Further handling of the plants

8. SELECTION OF PARENTS
The choice of the parents depends on the objective of the cross. In
combination breeding, the genetic diversity of the parents is not
important. In the case of transgressive breeding, genetically diverse
plants are selected as parents. If the characteristics of the parents are
not completely known, they are evaluated for the agronomic features.

9. EMASCULATION
In the case of crops with bisexual flowers, stamens of the flowers of the
female parents are removed or the pollen grains are killed. This process
is called emasculation. Mechanical, physiological or genetic methods of
emasculation are used, depending upon the nature of the crop and the
cross.

10. MECHANICAL METHODS OF
EMASCULATION
Here, the anthers are removed from the flowers of the female parents.
Hand emasculation and suction method are generally used. For hand
emasculation, the flower buds are opened carefully before anthesis (First
opening of the flower) and the anthers are removed with the help of
forceps. Care should be taken so that the gynoecium of the flowers in
not damaged. In suction method, the petals are removed from the
flowers before anthesis, with the help of forceps. Then, a thin rubber or
glass tube attached to a suction hose is used to suck the anthers from
the flowers.

11. PHYSIOLOGICAL METHODS OF
EMASCULATION
Here, the anthers are killed with the help of heat treatment, cold
treatment or alcohol treatment.

12. GENETIC EMASCULATION
Genetic or cytoplasmic male sterility factors are introduced into the
female parents to make them sterile.

13. BAGGING
The emasculated inflorescences of female plants are covered using
butter paper bags or cloth bags. However, in the case of cross-pollinated
crops, male plants may also be bagged if desired, so as to avoid pollen
mixture. The bags are removed 2-3 days after pollination.

14. TAGGING
Emasculated flowers are tagged properly after bagging. Circular or
rectangular tags may be used. Details of the cross, date of emasculation,
date of pollination and the number of flowers emasculated must be
noted on the tag. Carbon pencil or permanent ink may be used for
tagging.

15. POLLINATION
Mature, fertile and viable pollen grains are collected from the male
parent and dusted on the stigma of the female parent. Care should be
taken to see that the pollen grains are dusted at the optimum stage of
viability.

16. HARVESTING F1 SEEDS
Crossed seeds are harvested carefully and stored to raise the F1
generation.

17. FURTHER HANDLING OF THE PLANTS
Further handling of the hybrids depends on the objective of the cross. In
the case of hybrid seed production, the F1 seeds are directly released to
farmers. In the case of combination breeding and transgressive breeding,
F2 is raised and the most appropriate solution program is used.

18. POLYPLOIDY BREEDING
In somatic cells, chromosomes are present in homologous pairs whereas
in gametes chromosomes are present in single set. Hence, each organism
has two types of chromosome numbers, the somatic chromosome
number (2n) and the gametic chromosome number (n). However, each
genetic set is formed of either a group of different chromosomes or a
few groups of such chromosomes. Hence in some cases, the gametic set
consists of a few numbers of identical sets. Here, each of such sets
represents a basic set of chromosomes and the number of chromosomes
in such a set can be called the basic chromosome number (x). Hence n
may be equal to x, 2x, 3x etc. When n=x, the organism is diploid, when
n=2x, the organism is a tetraploid and when n=3x, it is a hexaploid (2n =
2x, 4x and 6x respectively). Besides the type of variation, absence or
additional presence of individual chromosomes can also be seen in
organisms. Such variations can be exploited in plant breeding because
they bring about desirable character changes in many cases.

19. VARIATIONS IN CHROMOSOME NUMBER
TYPE CHARACTERS
1. EUPLOIDY Numerical changes in the entire genome
(a) Monoploidy Only set of gamete (x)
(b) Haploidy Only the haploid (gametic) set of genomes (n)
(c) Diploidy Two sets of genomes (2x)
(d) Polyploidy More than 2 sets of genomes (3x onwards)
(i) Triploidy 3x
(ii) Tetraploidy 4x
(iii) Pentaploidy 5x
(iv) Hexaploidy 6x
2. ANEUPLOIDY Change in the number of a one or a few
chromosomes
(a) Hypoploidy Loss of chromosomes from the diploid set
(i) Monosomy Loss of one chromosome from the diploid set (2n - 1)
(ii) Nullisomy Loss of one chromosome pair from the set (2n - 2)
(b) Hyperploidy Additional presence of chromosomes along with the
diploid set
(i) Trisomy Addition of one chromosome to the set (2n + 1)

20. HAPLOIDY BREEDING
• Haploids can be used in many ways in plant improvement. They are
useful for the development of pure lines and inbred lines and for the
production of aneuploids. Pure lines can be obtained by chromosome
doubling of haploids. Such pure lines can be used as cultivars or parents
in hybridization.
• PRODUCTION OF HAPLOIDS
Haploids originate spontaneously in small numbers. Haploid production
can be induced by inter-specific cross, use of alien cytoplasm, anther
culture, pollination with foreign pollen, use of irradiated pollen, chemical
treatment etc.

21. THE END