6 years of maize selection in kitale synthetic ii ecuador 573 and kitale composite a using methods of the comprehensive breeding system
Darrah, L.L.; Eberhart, S.A.; Penny, L.H.
Euphytica 27(1): 191-204
1978
ISSN/ISBN: 0014-2336 Document Number: 499105
The Kitale [Kenya] maize [Zea mays] breeding study proved that reciprocal recurrent selection is an effective interpopulation improvement method. Ear-to-row selection was effective in improving 'Kitale Composite A' (KCA). Data from a diallel of the cycle-6 ear-to-row substrains showed that where less than 10 lines were selected, inbreeding apparently depressed gain, but differences among the various ear-to-row experiments were not significant. Intercrossing the substrains was predicted to reduce the effect of inbreeding. Yield gains in reciprocal recurrent selection and ear-to-row selection were associated with increases in ears per 100 plants. The reciprocal recurrent selection variety cross yield gain was estimated at 3.5% per yr (7%/cycle) and that of the best ear-to-row procedure at 2.6% per yr. The variety cross syn-2 from reciprocal recurrent selection was predicted to improve at the same rate as the best ear-to-row procedure (E7) with 1 long growing season per year. Under a cropping system with 2 similar seasons/year, however, ear-to-row selection should be more effective than reciprocal recurrent selection or its derived syn-2. Mass selection at 10% selection intensity produced significant improvement, but not at 2% intensity. S1 and 3 half-sib selection methods were ineffective in KCA. Inbreeding and the lack of linkage equilibrium in KCA were discussed as contributing. Theoretical substrain compositing required 30-40 lines selected to equal the effectiveness of ear-to-row selection with 10 lines. Full-sib selection was effective in improving yield at 1.2%/yr. All the recurrent selection methods showed a significant increase in ears per 100 plants. Population size was important in reducing losses due to inbreeding. If a hybrid or variety cross is potentially usable, reciprocal recurrent selection provides the best population approach. Initially, the variety cross syn-2 could be released with no additional breeding effort. Transition to variety crosses or traditional hybrids from extracted lines could be done as farmer husbandry improves and seed production facilities develop. Otherwise, open-pollinated varieties superior to existing maizes can be effectively developed using ear-to-row selection. The other methods may be effective in breeding populations when larger effective population sizes are used, but they were not effective in KCA when only 10 lines were recombined each cycle.