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Procedure
- The selection of parents to be used in a cross is the most important step in a breeding programme based on hybridization.
- The selected parents are crossed to produce a simple or a complex cross.
- For convenience, we refer to the seed obtained from both simple and complex crosses as the F1 seed.
- F1 seeds are space-planted so that each F1 plant produces the maximum number of F2 seed. Ordinarily, 15-30 F1 plants should produce enough seed for a good F2 population.
- In F2, 2,000-10,000 plants are space-planted to facilitate selection.
- About 100-500 plants are selected and their seeds are harvested separately.
- Usually, the F2 population size should be 10-100 time the number of F2 plants that are to be selected.
- The number of F3 progenies may vary from 100-500 depending upon the facilities available and the objectives of the breeding programme.
- When closely related varieties are crossed, the number of F3 progenies maintained would be considerably smaller than when the parent varieties are unrelated by descent.
- When the objective of breeding is to improve yield, to recover transgressive segregants, or both, a relatively larger number of F2 plants would be selected.
- Individual plant progenies are space-planted. Each progeny should have about 30 or more plants.
- Individual plants with desirable characteristics are selected particularly from superior progenies.
- Outstanding plants from inferior progenies may also be selected.
- Disease and lodging susceptible progenies and progenies with undesirable characteristics are eliminated.
- The number of plants selected in F3 should be preferably less than that of the F3 progenies.
- If the number of superior progenies is small, the whole cross may be rejected.
- Individual plant progenies are space-planted. Again, desirable plants are selected mainly from superior progenies.
- The number of plants selected in F4 is generally much smaller than that of the progenies raised in F4.
- Progenies with defects and undesirable characteristics are rejected.
- If two or more progenies coming from the same F3 progeny are similar and comparable, only one of them may be saved and the others may be rejected.
- Thus the emphasis is on selection of desirable plants from superior progenies.
- Individual plant progenies are generally planted according to the recommended commercial seed rate.
- Often three or more rows are grown for each progeny to facilitate comparison among progenies.
- Many families would have become reasonably homozygous and may be harvested in bulk.
- In families showing segregation, individual plants are selected.
- The breeders have to visually assess the yielding potential of progenies and reject the inferior ones.
- The number of progenies must be reduced to a size manageable in preliminary yield trials, which are usually 25-100 progenies.
- Individual plant progenies are planted in multi-row plots and evaluated visually. Progenies are harvested in bulk since they would have become almost homozygous. Progenies showing segregation may be eliminated unless they are outstanding; in such progenies individual plants may be selected. Preliminary yield trial is usually planted in F6 for those progenies, which are reasonably homozygous and have enough seed. Inferior progenies are eliminated based on yield data from preliminary yield trials and visual evaluation.
- Preliminary yield trials with 3 or more replications are conducted to identify a few superior lines.
- The progenies are evaluated for plant height, lodging, disease resistance, flowering time, maturity time etc., quality tests for produce, organoleptic evaluation may serve as additional criteria for selection.
- Standard commercial varieties must be included as checks for comparison. Two to five outstanding lines, if superior to the checks, would be advanced to the coordinated yield trials.
- The superior lines are tested in replicated yield trials at several locations.
- The lines are evaluated for yield, disease and lodging resistance, maturity time and quality including organoleptic quality etc., line that is superior to the best commercial variety included in the trial as check in yield and other characteristics is identified for release as a new variety.
- When a strain is likely to be released as a variety, the breeder usually multiples its seed during its last year in trial
- The breeder has the responsibility to supply the breeder’s seed to the National Seeds Corporation, which is responsible for the production of foundation seed.
- Thus in F11 and F12, the seed of the new variety will be multiplied for distribution to the farmers.
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Participants