Studies on the efficiency of two breeding methods applied to improve yield and quality in two maize populations carrying Brachytic-2, Opaque-2 and Sugary-2 genes
A study was conducted on normal KCR and KCE and their modified mutant populations carrying brachytic-2, opaque-2 and sugary-2 genes. The objective was to study the effect of three mutant genes on yield and protein characters, the eff'_ciency of two recurrent selection methods (reciprocalrecurrent selection and Sl testing methods) and an attempt to improve grain yield, the appearance and the texture of opaque grains. After formation of the two triple mutant populations of KCB and KCE, they were improved using the two methods separately through one cycle. The improved populations, their hybrids and previously converted ~opulations together with four commercial checks making a total of ?5 entries were evaluated in 5 x 5 triple lattice designs at four locations. Results showed that the brac~ytic-2 gene ~ay or may not affect grain yield, but cefinitely reduced plant and ear height; it improved lodging resistance and kept the leaf number constant. It failed to improve the crop index. The opaque-2 gene improved n~tritional value but lowered the grain yield; it made grains much more susceptible to pests and diseases. Modified grains with varying frequencies rectif~ed some of the opaque defects. Double mutant population had better yields, and quality characters; this was probably due to the favourable epistatic interactions between the tw6 genes. However, at the triple mutant level tremendous improvement was realised. The relationships between yield and quality traits were negative. KCE population made faster genetic gains than KCB. The reciprocal recurrent selection was much more efficient than Sl testing. Introgression of genes from KCB population into KCE and vice versa, that took. place at the time of formation affected their response to heterosis un+avoureb Iv. However, after one cycle of selectiol in both methods the populations responded positively. Breeding programmes for the release of open pollinated varieties may have a choice between Sl testing and reciprocal recurrent ~el8ction methods, depending on the skill of labour and available resources. However, in view of a programme for hybrid production, reciprocal recurrent selection is the most appropriate. It wou~J be difficult to encourage the production of high protein quality maize if it yielded less than normal maize. In this study it was clearly indicated that the yield performance of triple mutant hybrids was equal to the best commercial hybrid grown in Kenya and as good as their normal counterparts. ThEre is scope for further improvement in triple mutan£ populations and their hybrids using any of tre recurrent selection procedures. The role of "genetic modifiers needs to be studied further particularly . their inheritance.