This is paper presented at department of plant biology, Bayero university, Kano. the paper talks extensible on Methods involves in hybridization

1. Term Paper presentation on the
topic: methods involve in
hybridization and selection
by
Isah Salisu

2. Introduction
 Hybridization
 Hybrid
 Selection
 Most breeding methods incorporate sexual hybridization as a method of generating
new genetic variability.
 Hybridization may occur naturally, as in the case of out-crossing species, or it may
require tedious manipulation of flowers in the case of a self-pollinating species.
 In special cases, sexual hybridization has been used as a method to combine traits
from species that are rarely cross-fertile.

3. Inroduction cont…
Generally the method of hybridization and selection to be employ by breeders depend
on the mode of pollination and propagation of the plants species to be hybridize.
 self-pollinated species
 Outcrossing species
 Vegetative Propagated species

4. Methods Involve In Hybridization And Selection
Of Self-Pollinated species
 Pedigree method
 Single seed descent method
 Bulk method
 Back cross method

5. Pedigree method
 selection method, which is used in segregating population of self-pollinated
species and keeps proper record of plants and progeny selected in each
generation is known as pedigree breeding.
 This method is widely used for the development of varieties in self-pollinated
crops.
 In this method individual plants are selected till the progenies become
homozygous.
 Selection for plants in the desired combination of characters is started in the F
generation and continued in succeeding generations until genetic purity is
reached.
 Due to successive self-pollination most of the lines become homozygous and
uniform.

6. Pedigree method Cont…
Advantages of pedigree Method
 It is the quickest method.
 Plant breeders can also obtain the genetic information.
 There are chances of recovering transgenic segregation by this method.
Disadvantages of pedigree Method
 Maintenance of accurate pedigree record is not easy. It takes much time.
 Selected material becomes so large that handling of the same becomes very
difficult.
 Success of this method depends upon the skill of the breeder.

7. Single-Seed Descent Method
 The single-seed descent (SSD) method addresses all the short comings of pedigree
method mentioned above.
 This method select lines and families in early generations, a large F2 population is
created, and one random line is developed from each F2.
 Thus, the pedigree of each F2 line is represented by exactly one random line in each
following generation by taking a single seed from each F2 family in every segregating
generation.
Advantages of Single-Seed Descent Method
 The SSD method can also be used to derive populations of nearly inbred lines (NILs).
).
 These populations are useful in genetic experiments because segregation can be
considered random such that “good” lines can be contrasted with “bad” lines to identify
genetic determinants.

8. Single-Seed Descent Method Cont..
Disadvantages of Single-Seed Descent Method
 Lack of roper record keeping.
 Information on the inheritance of characters cannot be obtained.

9. Bulk Methods
 A bulk breeding method is any method whereby generations are advanced by
bulking and planting seed from the previous generation.
 However, if all seed from a given generation is harvested, then there will likely be
too much seed to plant in the following generation, so some seed must be
discarded or held in reserve.
 The SSD method is actually a special type of bulk breeding whereby each
generation is advanced by saving only one seed per plant from the previous
generation.
 In other methods of bulk breeding, the reduction of seed is achieved randomly, or
through a selection process that is applied uniformly but indiscriminately.

10. Bulk Methods Cont…
Advantages of Bulk Methods
 The bulk method is simple, convenient, inexpensive and less labour consuming
(no pedigree record is to be kept).
 During early segregating generations, very little work and attention is needed,
which gives the breeder more time to concentrate on other breeding projects.
 Selection is done by nature only and it increases the frequency of superior types
in the population.
 This method is suitable for studies on the survival of genes and genotypes in
populations.

11. Bulk Methods Cont…
Disadvantages of Bulk Methods
 This method takes much longer time to develop a new variety.
 The breeder is enable to exercise his skill and judgment in selection and therefore
the method is less satisfying to him.
 Information on the inheritance of characters cannot be obtained.
 This method is totally dependent on natural selection to select the superior types.
These types may not be necessarily the best yielding types.

12. Backcross Method.
 Backcross breeding method is quite different from the methods discussed so far.
It involves much smaller populations and greater numbers of hybridizations.
 The objective of a backcrossing program is to preserve as many genes as
possible in an inbred parent that has proven adaptation to a given environment.
 Each time a backcross is made, the progeny receive half their alleles from each
parent; thus, the proportion of alleles that remain from the donor parent are
reduced by 50% each generation.

13. Backcross Method. Cont…
Advantages Backcross Method
 This is the most common method used for transfer for oligogenic character like
disease resistance.
 Role of environment is almost negligible. So time required for developing new
variety may be drastically reduced because off-season nurseries and
greenhouses can be used for developing 2-3 generations each year.
 Breeder does not require to handle large populations.
 Extensive yield tests are not required because the performance of the recurrent
parent is already known.

14. Backcross Method. Cont…
Disadvantages of Backcross Method.
 The new variety is superior over the already available variety only in the
transferred character.
 Hybridization has to be done for each backcross. It requires lot of time and
money.
 Sometimes undesirable genes are closely linked with desirable one and get
transferred to the new variety.

15. Methods of Hybridization and selection
in Cross- Pollinated Species
 Like self-pollinated species, hybridization in cross-pollinated species involves
crossing of two or More inbreeds.
 Inbreeds are combined in any one of the following types of crosses;
(1) Single cross:
 Crossing of two inbreeds or varieties are called single cross such as A x B or C x
D. This cross was proposed by Shull (1909).
 The total number of possible different single crosses produced by a given number
of inbreeds can be calculated by the formula n (n-1)/2 where n is the number of
inbreeds. e.g., from four inbreeds six single crosses can be produced.

16. Cont…
2. Double Cross:
 Commercial hybrids are produced by this method. These hybrids give very high
yield in small land without any increase in the cost of production. All the hybrid
seeds of maize to farmers for cultivation are nothing but double crosses.
 It can be three-way cross, e.g. a cross of a single cross (used as female) with
another inbred (used as male), i.e., it involves three inbreeds [(A x B) x C],
 It can also be synthetic cross i.e, cross among inbreeds, clones or sibbed lines
without control of pollination.
 This is the cross of a number (4-10) pretested hybrids and is done by open
pollination in isolation.
 Seeds of these inbreeds are mixed in equal proportion and sown in isolated plots.
Natural cross pollination takes place and the harvested produce becomes
synthetic cross. This cross is used in forage cross where floral structure causes
difficulties in artificial pollination.

17. Methods of Hybridization and Selection
in Vegetative Propagated species
 Some crop plants are propagated naturally and/or artificially through
vegetative propagation rather than through sexually produced seeds.
 Improved clones of asexually propagating plants are selected and
allowed to grow under conditions, which favour flowering and seed
setting.
 Desirable clones are crossed together and the hybrids are multiplied by
cloning. Each F plant is a potential source for a new clone. This
procedure has been used for developing many improved varieties of
sugarcane, potato etc. (Calam, 2009).