Principles and method of breeding in cross pollinated crops

1. College of Horticulture and Forestry, Pasighat
Central Agricultural University, Imphal
Assignment
Course :- Breeding of Vegetable Crops (VSC 503)
Topic :- Principles and methods of breeding in cross
pollinated crops
To
Dr. Nangsol Dolma Bhutia
Assistant Professor
Department of Vegetable Science
College of Horticulture and Forestry
Pasighat
From
Teju C M
04-H(M)-20
M.Sc. Vegetable Science
CHF, Pasighat

2. PRINCIPLES AND METHODS OF BREEDING IN CROSS POLLINATED CROPS
Introduction
Various approaches that are used for genetic improvement of crop plants are referred to as plant
breeding methods.
The choice of breeding methods mainly depends on;
 The mode of pollination,
 Mode of reproduction,
 Gene action and
 Breeding objective of crop species
Cross pollination – One flower is pollinated by the pollen of different flower either from same
plant or different plant.
Mechanism promoting cross-
1) DICLINY: It refers to unisexual flowers. This is of two types: i) monoecy and ii)
dioecy. When male and female flowers are separate but present in the same plants, it is known
as monoecy. In some crops, the male and female flowers are present in the same inflorescence
such as in mango, castor and banana. In some cases, they are on separate inflorescence as in
maize. Other examples are cucurbits, grapes, strawberry, cassava and rubber. When staminate
and pistillate flowers are present on different plants, it is called dioecy. It includes papaya,
date palm, spinach, hemp and asparagus.
2) DICHOGAMY: (from the Greek dikho-apart and gamous-marriage) It refers to maturation of
anthers and stigma of the same flowers at different times. Dichogamy promotes cross
pollination even in the hermaphrodite species. Dichogamy is of two types: viz. i) protogyny
and ii) protandry. When pistil matures before anthers, it is called protogyny such as in pearl
millet. When anthers mature before pistil, it is known as protandry. It is found in maize,
sugarbeet and several other species.
3) HETEROSTYLY: When styles and filaments in a flower are of different lengths, it is called
heterostyly. It promotes cross pollination, such as linseed.
4) HERKOGAMY: Hinderance to self-pollination due to some physical barriers such as
presence of hyline membrane around the anther is known as herkogamy. Such membrane does
not allow the dehiscence of pollen and prevents self-pollination such as in alfalfa.
5) SELF-INCOMPATIBILITY: The inability of fertile pollens to fertilize the same flower is
referred to as self-incompatibility. It prevents self-pollination and promotes cross pollination.
Self-incompatibility is found in several crop species like Brassica, Radish, Nicotiana, and
many grass species. It is of two types sporophytic and gametophytic.

3. 6) MALE STERILITY: In some species, the pollen grains are non-functional. Such condition
is known as male sterility. It prevents self-pollination and promotes cross pollination. It is of
three types: viz. genetic, cytoplasmic and cytoplasmic genetic. It is a useful tool in hybrid seed
production
Characteristics of cross pollinated plants
1) Each genotype has equal chances of mating with all other genotypes.
2) Plants are highly heterozygous in nature.
3) Higher degree of inbreeding depression.
4) Wide adaptability and more flexibility to environmental changes due to heterozygosity and
heterogenity.
5) Cross pollination permits new gene combinations from different sources.
6) Individuals have deleterious recessive gene which are concealed by masking effect of
dominant genes.
Methods of breeding in cross pollinated crops
1) PLANT INTRODUCTION.
2) MASS AND PROGENY SELECTION.
3) RECCURRENT SELECTION.
4) HETEROSIS BREEDING.
5) BACK CROSS METHOD.
6) SYNTHETIC AND COMPOSITE BREEDING.
7) MUTATION BREEDING.
8) POLYPLOIDY BREEDING

4. 1) PLANT INTRODUCTION:
 Plant introduction consists of taking a genotype or a group of genotypes of plants into new
environments. where they were not being grown before.
 It is an oldest and rapid method of crop improvement.
STEPS OF INTRODUCTION:
1. Procurement
2. Quarantine
3. Cataloguing
4. Evaluation
5. Multiplication and Distribution
The chief objectives
 To Obtain an anetirely new crop plant.
 To serve as new varieties.
 To be used in crop improvement.
 To save the crop from diseases and pests.
 For scientific studies.
1) Primary Introduction :
o When the introduced variety is well suited to the new environment, it is released for
commercial cultivation without any alteration in the original genotype, this constitutes primary
introduction.
o Primary introduction is less common, particularly in countries having well organized crop
improvement programmers.
2) Secondary Introduction:
o The introduced variety may be subjected to selection to isolate a superior variety. Alternatively,
it may be hybridized with local varieties to transfer one or few characters from this variety to
the local ones these processes are known as secondary introduction.
o Secondary introduction is much more common than primary introduction.

5. Merits of Plant Introduction
1) It provides entirely new crop plants.
2) It provides superior varieties either directly or after selection & hybridization.
3) Introduction and exploration are the only feasible means of collecting germplasm and to protect
variability from genetic erosion.
4) It is very quick & economical method of crop improvement, particularly when the
introductions are released as varieties either directly or after a simple selection.
5) Plants may be introduced in new disease-free areas to protect them from damage.
Demerits of Plant Introduction
The disadvantages of plant introduction are associated with chances the introduction of
weeds, diseases and pests.

6. 2) MASS SELECTION AND PROGENY SELECTION
 MASS SELECTION
 Mass selection is often described as the oldest method of breeding.
 Mass selection is an example of selection from a biologically variable population.
 Selection is based on plant phenotype.
Types of mass selection
a) Positive mass selection:
 Desirable plants are selected from a mixed population.
 Their seeds are mixed together to grow further generation.
 This process is continued for several years.
 Old varieties or land races are used as the base material.
b) Negative mass selection:
 Only undesirable off types of plants are removed from the field and rest are allowed to
grow.
 Generally used for Varietal purification in seed production.
 Helps in maintaining high level of genetic purity.
Steps of Mass selection:
1. Selection of base population.
2. Selection of desirable plants from the base population.
3. Mixing their seeds to raise next generation.
4. Evaluation in field trials.
5. Releasing as a new variety.

7. Merits of Mass Selection
 Rapid and Simple breeding method.
 Selection cycle is very short.
 Have high heritability.
 Effective in improving yield of cross pollinated crops.
Demerits of Mass Selection
 Phenotypic performance is greatly influenced by environmental factors.
 No control on the pollination.
 Inbreeding depression.
 PROGENY SELECTION
o The simplest form of progeny selection is ear-to-row method
o Developed by Hopkins (1908)
o This method was extensively used in Maize
 It should be seen that ear-to-row method is relatively simple and the selection cycle is of one
year only

8.  However it suffers from the defect that plants in the superior progenies are pollinated by those
in both the superior and inferior progenies; this reduces the effectiveness of selection
MODIFICATION IN EAR TO ROW SYSTEM
Merits of progeny selection
a. It is based on progeny test and not on the phenotypes of individual plants hence it is far more
accurate reflection of the genotype than phenotype
b. Inbreeding may be avoided if care is taken to select a sufficiently large number of plant
progenies
c. Selection scheme is relatively simple and easy
Demerits of progeny selection
a. There is no control on pollination and plants are allowed to open-pollinate. Thus the selection
is based on the maternal parent only
b. The selection time is two years. Thus the time required for selection is as much as in the case
of mass selection

9. 3) RECURRENT SELECTION
o Reselection of generation after generation with inter breeding of selected plants to provide for
genetic recombination.
o The procedure of Recurrent selection was described by Jenkins in 1940.
o The term Recurrent selection was given by Hull in 1945.
TYPES OF RECURRENT SELECTION
1) Simple recurrent selection.
2) Recurrent selection for general combining ability.
3) Recurrent selection for specific combining ability.
4) Reciprocal recurrent selection.
1. Simple Recurrent selection
 Selection is based on Phenotypic characters of plants.
 Tester is not used in this scheme.
 It does not measure the combining ability.
 This method is useful only for those characters which have high heritability.
2. Recurrent selection for general combining ability.
 In this method selection is based on heterozygous tester cross performance.
 Improves general combining ability of population for a character.

10.  This method is used for genetic improvement of quantitative characters.
 Improves those characters governed by additive gene action.
3. Recurrent selection for specific combining ability.
 In this method selection is based on Homozygous tester cross performance.
 Improves specific combining ability of population for a character.
 This method is used for genetic improvement of polygenic characters.

11. 4. Reciprocal recurrent selection
 In this method two heterozygous testers are used for crossing. This scheme was proposed by
Comstock,et al. in 1949.
 Improves both GCA and SCA of population for a character.
 This method is used for genetic improvement of polygenic characters.
 This method is also known as recurrent reciprocal half sib selection.
Merits of Recurrent Method
 Recurrent selection is efficient breeding method for increasing the frequency of superior genes
in a population.
 It helps in maintaining high genetic variability in a population due to repeated intermating of
heterozygous population.
 The selection is made on the basis of test cross performance and only selected plants are
allowed for inter mating.
Demerits of Recurrent Method
 This method permits selfing which leads to loss of genetic variability.
 This method is not used directly for the development of new varieties.
 This method involves lot of selection, crossing and selfing work.

12. 4) HETEROSIS BREEDING
HETEROSIS
 Heterosis refers to the superiority of F1 hybrids in one or more characters over its parents.
 The term hybrid vigour is used as synonym for heterosis.
 The term heterosis was first used by Shull in 1914.
HYBRID VIGOUR:
According to Shull, the developed superiority of the hybrid is the hybrid vigor.
SPECIFIC FEATURE OF HETEROSIS
 Superiority over Parents.
 Heterosis leads to superiority in adaptation, yield, quality, disease resistance, maturity and
general vigor over its parents.
 Generally, positive heterosis is considered as desirable. But in some cases negative heterosis
is also desirable.
IMPORTANT FEATURES OF HETEROSIS
 Superiority of over parents
 Confined to FI
 Genetic control
 Reproducible
 Association with specific combining ability
 Effect of heterozygosity
 Conceals recessive genes
 Low frequency
MANIFESTATION OF HETEROSIS
 Increased yield
 Increased reproductive ability
 Increased size and general vigour
 Better quality
 Earlier flowering and maturity
 Greater resistance to diseases and pests
 Greater adaptability and faster growth rate.

13.  GENETIC BASIS OF HETEROSIS
The genetical basis of heterosis is still following two hypothesis:
1) Dominance hypothesis of heterosis.
2) Over dominance hypothesis of heterosis.
1) DOMINANCE HYPOTHESIS OF HETEROSIS
Holds that increased vigor and size in a hybrid is due to combination of favorable growth
genes by crossing inbred lines.
2) OVER DOMINANCE HYPOTHESIS OF HETEROSIS
Considered that there is a physiological stimulus to development that increases with the
diversity of the uniting gametes.
TYPES OF HETEROSIS
a) ON THE BASIS OF ORIGIN AND NATURE
A. EU-HETEROSIS OR TRUE HETEROSIS
1. Mutational heterosis
2. Balanced heterosis
B. PSEUDO HETEROSIS
b) ON THE BASIS OF TYPE OF ESTIMATION
1. AVERAGE HETEROSIS
2. HETEROBELTIOSIS HETEROSIS
3. USEFUL HETEROSIS

14. 1.Mutational heterosis
Lethal (mostly), recessive, adaptively unfavorable mutants are either eliminated by their
non-lethal dominant and adaptively superior alleles in cross pollinated crops.
2.Balanced heterosis
Well balanced gene combinations which are more adaptive to environmental conditions
and useful from the agriculture point of view result in balanced heterosis.
3.Pseudoheterosis
Also termed as an luxuriance. progeny poses superiority over parents is in vegetative
growth, but not in yield and adaptation, usually sterile or poorly fertile. this concept cannot be
utilized in hybrid varieties production.
ON THE BASIS OF TYPE OF ESTIMATION
1. Average or relative heterosis:
When heterosis is estimated over mid parent value i.e. average of two parents value.
2. Heterobeltiosis:
When heterosis is estimated over better parent it is called heterobeltiosis.
3. Standard heterosis:
 When heterosis is estimated over standard commercial hybrid it is called as standard
heterosis.
 It has practical importance in plant breeding.
 It is also referred as a useful or economic heterosis
FACTORS AFFECTING HETEROSIS
There are four genetic factors which affect magnitude of heterosis in crop plants.
a. Mode of Pollination
b. Genetic Diversity of Parents
c. Genetic base of Parents
d. Adaptability of Parents

15. 5) BACK CROSS METHOD:
It is a cross between a segregating F1 and one of its parent.
 Back cross method: In this method, the hybrid and the progenies in the subsequent
generations are repeatedly back crossed to one of their parents.
 Objective: To improve or correct one or two specific defects of a high yielding variety,
which is well adapted to the area and has other desirable characteristics.
 Recipient parent: Well adapted, high yielding variety, lacking one or two characters and
hence receives these genes from other variety. As it is repeatedly used in the process this
is also known as recurrent parent.
 Donor parent: The variety which donates one or two useful genes also known as Non-
recurrent parent.
TRANSFER OF DOMINANT GENE-
 If “A” is a well adapted commercial cultivar lacking in a trait, this is crossed with a variety B
which has that desirable trait.(let the trait be powdery mildew resistance)
 BC1 - all are resistance due to dominant nature if the gene expression , so selection is not
needed , it is directly crossed with the recurrent parent.
 BC2– 50% plants show resistance, so they are selected and rest all are roughed out, theses
selected plants are subjected to crossing again with the recurrent parent.
 BC3 to BC5 – same process as above , i.e., selection and crossing with recurrent parent is
done.

16.  BC6 – now the selected 50% of plants having resistance will be having approx.. 98.4% of gene
from recurrent parent A and a desirable gene of interest from parent B or donor parent, i.e.,
resistance
These plants are selfed to get F2 generation and seeds are harvested separately.
 BC6 F2- Individual plant progenies are grown and selection is done for plants which are
showing resistance and are homozygous. They are harvested and seeds are bulked which
constitute a new variety with all traits from parent A and resistance gene from parent B.
 This new variety is subjected to yield trials ,then evaluated and released.
TRANSFER OF A RECESSIVE GENE
 Hybridization: The recurrent parent is crossed with the disease resistant donor parent. The
recurrent parent is generally used as the female parent.
 F1 Generation: F1 plants are backcrossed to the recurrent parent.
 BC1 Generation: Since resistance is recessive, all the plants will be disease susceptible. All
the plants are selfpollinated.
 BC1 F2 Generation: Plants are inoculated with disease. Disease resistant plants are selected
and backcrossed with the recurrent parent. Selection is done for the plant type and other
characteristics of the variety A.

17.  BC2 Generation: Plants are selected for their resemblance to the recurrent parent A, and
backcrossed with the recurrent parent.
 BC3 Generation: The plants are self-pollinated to raise F2. Selection is usually done for the
plant type of variety A.
 BC3F2 Generation: Resistant plants resembling variety A are selected and backcrossed to
variety A. Selection for plant type of A is generally effective.
 BC4 Generation: Plants are back-crossed to variety A. BC5 Generation: Plants are self-
pollinated to raise F2 generation.
 BC5F2 Generation: A rigid selection is done for disease resistance and for the characteristics
of variety A. Selfed seeds from the selected plants are harvested separately.
 BC5F3 Generation: Individual plant progenies are grown and subjected to disease
epiphytotic. Selection is done for resistance and for the characteristics of variety A.
 After this yield trials are done for evaluation and are released as a new variety.
Merits of Backcross Method -
 The genotype of new variety is nearly identical with that of the recurrent parent, except for the
gene transfer.
 Much smaller population is needed in this method than in pedigree method.
 There is the only method for inter-specific gene transfers, and for the transfer of cytoplasm.
 Susceptibility in a well adapted variety can be removed without affecting its performance and
adaptability.
Demerits -
 The new variety generally cannot be superior to the recurrent parent, except for the character
that is transferred.
 Linkage drag (close linkage between a desirable and undesirable gene.)
 Hybridization required for each backcross; which is often difficult, time taking and costly.

18. 6) SYNTHETIC AND COMPOSITE VARIETIES
A) SYNTHETIC VARIETIES
o A variety produced by crossing in all combinations a number of lines that combine well with
each other is known as a synthetic variety
o Once synthesized, a synthetic is maintained by open pollination in isolation
o The lines that make up a synthetic variety may be inbred lines, clones, open-pollinated
varieties, short term inbred lines or other populations tested for GCA or for combining ability
with each other.
Operations in producing a synthetic variety
1. Evaluation of lines for GCA
2. Production of synthetic variety
3. Multiplication of synthetic variety
1.EVALUATION OF LINES FOR GCA
 GCA of the lines to be used as parents of synthetic varieties is generally estimated by top
cross or poly cross test
 Poly cross refers to the progeny of a line produced by pollination with a random sample of
pollen from a number of selected lines
 The lines are evaluated for GCA because synthetic varieties exploit that portion of
heterosis, which is produced by GCA.
2.PRODUCTION OF SYNTHETIC VARIETY
Method-1
 Equal amounts of seeds from the parental lines are mixed and planted in isolation
 Open-pollination is allowed and is expected to produce crosses in all possible combinations
 Seed is harvested in bulk; the population raised from this seed is the syn, generation
Method-2
 All possible crosses among the selected lines are made in isolation
 Equal amounts of seed from all the crosses is composited to produce the syn, generation

19. Available experimental evidence suggests that both the above methods produce comparable
results
3.MULTIPLICATION OF SYNTHETIC VARIETIES
 After a synthetic variety has been synthesized, it is generally multiplied in isolation for one
or more generations before its distribution for cultivation.
 The synthetic varieties are usually maintained by open-pollination seed and may be further
improved through population improvement schemes particularly through recurrent
selection.
MERITS
 Offers a feasible means of utilizing heterosis in crop species where pollination control is
difficult
 Farmers can use the grain produced from a synthetic variety as seed to raise the next crop.
 In variable environments synthetics are likely to do better than hybrid varieties
 Cost of seed in case of synthetics is relatively lower than that of hybrid varieties
 Synthetic varieties are good reservoirs of genetic variability
 Offers a possibility for continuous improvement of varieties
DEMERITS
 Performance of synthetics is usually lower than that of single cross and double cross hybrids.
 Performance of synthetics is adversely affected by lines with relatively poorer GCA. Such lines
often have to be included to increase the number of parental lines making up the synthetics as
lines with outstanding GCA are limited in number.
 Synthetics can be produced and maintained only in cross-pollinated crop species, while hybrid
varieties can be produced both in self and cross-pollinated crops.

20. B) COMPOSITE VARIETY:
 In cross pollinated crops, the mixture of genotype from several sources is maintained bulk from
one generation to the next is referred as composite variety. OR
 Composite variety is a variety derived from advance generation of random mated outstanding
lines (Germplasm inbreds, varieties, hybrids, advance generation lines).
 Mixing the seeds of several phenotypically outstanding lines produces a composite variety and
encouraging open pollination to produce crosses in all combinations among the mixed lines.
 The lines used to produce a composite variety are rarely tested for combining ability with each
other like synthetic composite are commercial varieties and are maintained by open-pollination
in isolation.
o The line used a produce a composite variety are rarely tested for combining ability with each
other.
o Mixing the seeds of various genotypes, which are similar in maturity height, seed size, colour,
etc. develops composite varieties.
o The variety is maintained by open pollination. Farmers can use their own seed for 3 to 4 years.
o The yields of composite verities cannot be predicted in advance, which is contrast to synthetic;
this is because of yield of all f, among the component lines are not available .Like synthetic,
composite are commercial varieties are maintained by open pollination in isolation. Another
type of population, called germplasm complexes are produced by mixing seeds from several
lines or populations of diverse genetic origin.
Procedure for Development Composite Variety:
1. There is no restriction to the number of lines included in the development of composite, but
the line possessing desirable characteristics should be selected like earliness, insect resistance,
drought and frost resistance can be included in the development.
2. The seeds of desired selected lines mixed together and random mating is allowed for 4-5
generations.
3. Such uniform population is tested in replicated trials, across environment along with standards
checks and high yielding stable type can be released as composite variety.
4. The combining ability of lines used in composite are not tested, whereas in synthetic each of
the component is tested for its combining ability.

21. Features of Composite Variety
o Heterogeneous
o Relevant to cross pollinated species only Can be developed from open pollinated variety any
other heterozygous variety.
o Farmer can use his own saved seed for 3 to 4 years, after that seed should be replaced.
o There can be two or more constituent genotypes.
DIFFERENCE B/W SYNTHETIC AND COMPOSITE VARIETIES
SYNTHETIC VARIETIES COMPOSITE VARIETIES
Crossing in all combination of number of lines
that combine well with each other
Mixing the seeds of several phenotypically
outstanding lines it and encouraging open
pollination to produce crosses in all
combination among the lines
4-10 numbers of parents are involved Many parents are involved
It is tested for GCA Not tested for GCA
Cost of less than composite variety Cost of seed is less than hybrid
It shows less heterosis than hybrid It shows more heterosis than synthetic
Reconstituted is done Reconstituted is never done
Maintenance of variety easy Maintenance of variety is difficult but easy
Prediction of performance possible Prediction of performance is not possible

22. 7) MUTATION BREEDING-
o Mutation is a sudden heritable change in a characteristic of an organism.
o Mutations produced by changes in the base sequences of genes are known as gene or point
mutations.
o The term mutations was introduced by Hugo de Vries in 1900 Spontaneous mutation Mutations
occur in natural populations (without any treatment by man) at a low rate. These are known as
spontaneous mutations.
o The frequency of natural mutations is generally one in ten lakhs Induced mutation Mutations
may be artificially induced by a treatment with certain physical or chemical agents. Such
mutations are known as induced mutations, and the agents used for producing them are termed
as mutagen. The utilization of induced mutations for crop improvement in known as mutation
breeding.
o Induced mutations have a great advantage over the spontaneous ones, they occur at a relatively
higher frequency so that it is practical to work with them.
Characteristics of mutations
 Mutations are generally recessive, but dominant mutations also occur.
 Mutations are generally harmful to the organism, but a small proportion (0.1 percent) of them
are beneficial.
 Mutations are random i.e., they may occur in any gene. However some genes show higher
mutations rate than others.
 Mutations are recurrent, that is the same mutations may occur again and again.
 Induced mutations commonly show pleiotropy, often due to mutations in closely linked genes.
Mutagen- Agents used for induction of mutations are known as mutagens. The mutagens are
classified into two groups, physical and chemical mutagens.
1.Physical mutagen -The mutations inducing radiation’s are of two kinds.
1. Ionizing radiation (x-rays, gamma rays)
2. Non ionizing radiation (Uv-rays)
2.Chemical mutagens
1. Alkylating agents – eg., EMS (Ethyl Methane Sulphonate) MMS (Methyl Methane
Sulphonate)
2. Acridine dyes eg., Ethidium Bromide, acriflavine proflavine
3. Base analogue – eg. 5 Bromouracil, 5 – Chlorouracil
4. Others - eg., Nitrous acid, hydoxyl amine , sodium azide

23. 8) POLYPLOIDY BREEDING-
The somatic chromosome number of any species, whether diploid or polyploidy, is
designated as 2n, and the chromosome number of gametes is denoted as n. An individual carrying
the gametic chromosome number, n, is known as haploid. A monoploid, on the other hand, has the
basic chromosome number, x. In a diploid species, n=x; one x122 constitutes a genome or
chromosome complement. The different chromosomes of a single genome are distinct from each
other in morphology and or gene content and homology; members of a single genome do not show
a tendency of pairing with each other. Thus a diploid species has two, a triploid has 3 and a
tetraploid has 4 genomes and so on.
Production of doubled chromosome numbers:
1. Spontaneous: chromosome doubling occurs occasionally in somatic tissues and unreduced
gametes are produced in low frequencies.
2. Production of adventitious buds: Decapitation in some plants leads to callus development at
the cut ends of the stem. Such a callus has some polyploid cells and some of the shoot buds
regenerated from the callus may be polyploidy.
o In solanaceous 6-36% of adventitious buds are tetraploids.
o The frequency of polyploid buds maybe increased by the application of 1% IAA at the cut
ends as it promotes callus development.
3. Treatment with physical agents: Heat or cold treatment centrifugation, x-ray or gamma ray
irradiation may produce polyploid. Exposing the plants or ears of maize to a temperature of
38-45 oC at the time of the first division of zygote produce 2-5 % tetraploid progeny.
4. Regeneration in vitro: polyploidy is a common feature of the cells cultured in-vitro.
5. Colchicine treatment: Colchicine treatment is the most effective and the most widely used
treatment for chromosome doubling.
Application of Auto polyploidy in Crop improvement
Triploids
Triploids are produced by hybridization between tetraploid and diploid strains. They are
generally highly sterile, except in a few cases. This feature is useful in the production of seedless
watermelons. Seedless watermelons are produced by crossing tetraploid (4x, used as female) and
diploid (2x, used as male) lines, since the reciprocal cross (2x x 4x) is not successful. The triploid
plants do not produce true seeds; almost all the seeds are small, white rudimentary structures like
cucumber (cucumis sativus) seeds. But few normal size seeds may occur which are generally
empty. For good seed setting pollination is essential. For this purpose diploid lines are planted in
the ratio 1 diploid: 5 triploid plants. There are several problem viz. genetic instability of 4x lines,
irregular fruit shape, a tendency towards hollowness of fruits, production of empty seeds and the
labor involved in triploid seed production.

24. BREEDING METHODS COMMON FOR BOTH SELF AND CROSS POLLINATED
CROPS:-
1. Introduction
2. Back cross method
3. Polyploidy breeding
4. Mutation Breeding
5. Transgenic breeding
In general wild species have wide adaptability but not have desirable characters like yield,
resistance, etc.., because undesirable crossings may occur in nature so that it's better to improve
the characteristics of plants so that they become more desirable agronomically and economically.
Various breeding methods which discussed above helps in creating genetic variability and
desirable crossings in plants.