This article throws light upon the top seven breeding methods of capsicum. The methods are: 1. Mass Selection 2. Pure line Selection 3. Pedigree Method 4. Single Seed Descent 5. Backcross Method 6. Heterosis Breeding 7. Mutation Breeding.
Method # 1. Mass Selection:
This is the simplest breeding technique to improve populations for multiple traits without concerns about pedigree. It must be used in an environment where the traits of interest are easily expressed. The efficiency of this technique is enhanced by rouging off type plants prior to flower opening.
Initially, it was used to improve landraces or open-pollinated cultivars of peppers. In this approach, characters with high heritabilities are easily fixed and a reasonable level of variability is also maintained. It is still used in Mexico to select seed for Poblano, guajillo and other traditional pepper landraces.
Method # 2. Pure line Selection:
This method is applicable to landraces/local cultivars being grown by farmers. In this method, initial seed stock is space planted and superior plants are selected and harvested separately.
Next year, individual plant progenies are grown and progeny showing superior performance and devoid of genetic variability, is bulk harvested and evaluated further with check cultivar(s) in replicated trials. Several chilli varieties in India have been developed by this method. These varieties are: G 1, G 2, G 3, G 4, NP 46A, K 1, Co 1, Musalwadi, Sindhur, Patna Red, Pant CI.
Method # 3. Pedigree Method:
This method involves selection of superior plants in the segregating generations following hybridization between superior cultivars along with maintenance of pedigree record. Selection of superior parental cultivars is crucial step in this method. Such chilli cultivars are Andhra Jyoti, Pusa Jwala, Pusa Sadabahar, X 235, K2, Punjab Lal and Jawahar 218.
Some examples in bell pepper in US are as follows:
Spartan Garnet – California Wonder X Dwarf Pimiento Selection from the variety Santanka
Spartan Emerald – Morgold x California Wonder
Sonnette-An F2 derived line originating from the cross (Morgold x California Wonder) x Keystone Resistant Giant
California Wonder is still a dominant and preferred variety and has been used rather frequently in new crosses. Therefore, in pedigree method, as far as possible, both the parental cultivars should be promising and superior types.
The process of generation advancement and selection continues for 6-8 generations when desired level of homozygosity is attained. This technique requires an environment, where traits of interest are expressed. Extensive experience with phenotypic evaluation is required and large F2 population (about 800-1000 plants) will facilitate selection for traits with low heritabilities or for polygenic traits like fruit yield, root volume, etc.
This method is often utilized in conjunction with backcrossing to introgress important genes into advanced inbreds. While advancing generations, steps to avoid out-crossing, such as caging of individual plants or manual pollination may be taken in peppers as although peppers are largely self-pollinated, but under certain situations, cross-pollination may be high in some peppers.
Method # 4. Single Seed Descent:
In this method, single pod seed is harvested from each plant in a segregating generation without much selection. In peppers, it is often carried out in greenhouse or winter nursery, to advance more generations in a year. This technique offers scope of selection for seed viability, seedling vigour, virus resistance or other single gene resistances amenable to controlled inoculation.
In pepper, SSD has been employed to fix recessive pot virus genes into the inbred lines prior to evaluating them in field for other economically important traits. This technique is widely employed how to generate large number of inbred lines to be used in test crosses for development of hybrids.
Method # 5. Backcross Method:
This is normally used to transfer single gene/few genes from primitive cultivars/wild forms on leading cultivars. In some cases even BC2 families may be routed through pedigree method of breeding (modified backcross) instead of following a routine backcrossing programme which needs 5-6 backcrosses with the recurrent parent.
After selection of gene of interest in F2 population, backcrossing begins. If the key gene is dominant, direct backcrossing may be done with selection at each generation.
If the gene is recessive, selfing should be done followed by selection, prior to each backcross, 6-8 generations are normally required. The typical examples are dominant L genes for TMV, recessive pvr, TEV resistance genes and various BLS resistance genes. Cultivars include Yolo Wonder R, Tabasco Green Leaf and Mississippi Nemaheart.
Method # 6. Heterosis Breeding:
F1 hybrids of bell pepper are popular in the USA and Europe and are gaining popularity in India after the initiation of research and seed production work in vegetables by a large number of private sector seed companies. The first hybrid variety in this crop in India was Bharat developed by Indo-American Hybrid Seeds, Bangalore (1973) followed by marketing of large number of hybrid cultivars by several other seed companies.
The greater success of hybrid cultivars in sell pepper could be attributed to:
(i) Sufficiently large flowers, easy emasculation and pollen in abundance
(ii) Large number of crossed seeds/fruit
(iii) Heterosis for yield
(iv) Easy deployment of dominant genes conferring resistance to diseases
(v) Highly remunerative price of hybrid seed
(vi) High yield potential of hybrids under better management and inputs
In India, private sector seed companies are going in a very aggressive way on hybrid development in hot-pepper, where current hot-pepper hybrid seed market is about 40 tons/year. The hybrid seed is produced through line x line, GMS and CMS system. In line x line system of hybrid seed production, 5 g female parent seed and 3 g male parent seed is used in a unit hybrid seed production plot of 1000 m2.
The seed quantity to be used in CMS system is also 5 g and 3 g respectively. However in case of GMS system where 50% fertile plants are to be removed from the female parent block, the seed quantity used is 10g and 3g respectively for female and male parent/unit hybrid seed production plot.
Good farmers harvest 30-40 kg hybrid seed/unit plot. Ideal time of hybrid seed production in Ranebennur of Karnataka and Deul Roja of Buldhana district of Maharashtra is Kharif Season. The market scenario of hybrids of hot-pepper in India is quite dynamic.
Method # 7. Mutation Breeding:
Mutation breeding has been found to be effective and efficient breeding tool in pepper, Daskalov (1986) has written an exhaustive review on this subject. The present write-up is based on this review.
The details are as follows:
For induction of mutations mainly seed treatments have been used. It is recommended to use seeds of uniform size, possessing 96-100% germ inability and moisture content (about 13%) to obtain good reproducibility of results.
It is difficult to determine the mutagen and dose that will yield the highest frequency of useful mutations. Therefore, 3 doses should be applied which are supposed to assure survival of 40 – 60% (LD40.60) after ionizing radiation treatments and 70 – 80% (LD20-30) following treatments with chemical mutagens.
Doses and treatment conditions used in mutation experiments are listed in Table 13.6 for general guidance. The dose range for gamma and X-rays is 60 – 400 Gy. The sweet cultivars usually are more radiosensitive than the hot ones.
Male gametophyte (mature pollen grains) at bi-nucleate stage (easy check can be made using aceto-carmine microscopic slides) are collected from already dehiscent anthers for mutagenic treatment. The dose range for gamma or X-rays is 5 – 15 Gy. Immediately after irradiation the pollen must be used for pollination of emasculated non-irradiated flowers.
The pollination is carried out in insect-proof glasshouses or the pollinated flowers are isolated with paper bags or cotton to avoid outcrossing. An alternative is the irradiation of the flowers with anthers before dehiscence (bi-nucleate stage) and the use of pollen for pollination of non-irradiated flowers.
For treatment of both gametophytes flowers just before anther dehiscence, must be labelled, all other buds and flowers removed and then the whole plants may be irradiated with gamma or X-rays. After the treatment, the plants are kept in a glass-house or if grown in open field, the flowers must be protected to avoid outcrossing.
Handling the M1 Generation:
M1 plants must be raised on isolated plots (at least 700 m apart from other pepper plantings) to prevent cross pollination. The use of recessive gene markers (e.g. lack of anthocyanin, marbled first leaves, yellow cotyledons) would help to detect contamination from cross-pollination. The safest procedure would be bagging of the M1 flowers to avoid outcrossing.
At least 3000-5000 M1 plants must be raised per experiment. It is recommended to harvest the fruits from the main bifurcation or those from each main branch. M1 plants are grown under optimal agronomic conditions to increase survival rate, secure optimal development and obtain sufficient fruit and seed setting.
Handling the M2 Generation:
20-25 M2 plants per M1 plant or 10 – 15 M2 plants per M1 fruit (with 2-3 fruits per M1 plant) are grown. The M1 plant or fruit-to-row method is commonly used by mutation scientists.
If the desired mutant character is very easily and distinctly recognizable on a single plant basis, the M1 bulk method may be used. It will save labour in M1 harvest, seed preparation, and labelling during planting. In this case, for each M1 plant 2 – 3 fruits from the main bifurcation and the main branches should be harvested and up to 15 seeds taken from each fruit to form the M2 bulk.
The size of the M2 field population that can be taken care of by one person is about 70,000- 100,000 plants but it depends, of course, on the kind of selection to be performed and the number of observations to be made. The selection of desirable mutants is carried out mainly in the M2 generation. To allow progeny testing all discovered mutants must be selfed, usually by bagging the flowers.
Handling the M3 Generation:
A progeny test is carried out from each suspected M2 mutant to confirm the mutation and examine the potential usefulness of the mutant. This process may continue up to M5 when mutants may be put in the trials.
Screening Techniques for the Selection of Particular Mutants:
(i) For CMV resistance:
Inoculation of M2 plants at four-leaf stage is done using the spraying technique. All plants, which do not show any symptoms must be inoculated again by the abrasion technique. Resistant plants are screened 10-20 days after inoculation.
(ii) For resistance to Phytophthora capsici Leonian (fruit rot):
Inoculation of M2 seedlings at the cotyledonary stage is done by dipping the roots in the inoculum prior to transplanting them into pots. Screening for resistant plants may start after 10-12 days.
(iii) For resistance to Verticillium dahliae, Kleb:
Inoculation of M2 seedlings at cotyledonary stage grown under glasshouse conditions at 24° ± 1°C is done by dipping the roots into the inoculum prior to transplanting them in pots. Screening for resistant plants may start after 20-30 days.
(iv) For male sterility:
20,000 – 25,000 M2 plants (about 1000 M2 families) obtained after gamma or X-irradiation of dry seeds must be screened during the flowering period. The male sterile mutants have flowers with very reduced and shrunken anthers containing no viable pollen grains. At the end of the vegetation period the male sterile plants are usually still flowering and possess lots of small parthenocarpic fruits. This makes them easily recognizable.
Released Mutant Cultivars:
According to Daskalov (1986) release of five mutant cultivars has been reported (Table 13.7).