Selection responses for the characters related to yield sink capacity of rice

Yield sink capacity, the maximum size of sink organs to be harvested, is an important target in breeding for high-yielding cultivars. Using two sets of F-2 and F-2:3 populations of rice (Oryza sativa L.), this study carried out disruptive selection in each F-2 population for every character related to yield sink capacity, evaluated the direct and correlated selection responses in their F-2:3 progenies, and estimated genetic correlations and realized heritabilities. Among the components of the number of spikelets per panicle, the umber of primary branches (PB) per panicle resulted in the highest realized heritability which exceeded the heritability for the number of spikelets per panicle. The genetic correlations indicated that the number of PB per panicle was positively and strongly associated with the number of spikelets per panicle in both populations. Thus, in one population, indirect selection on the number of spikelets per panicle via selection on the number of PB per panicle was slightly more effective than direct selection on the number of spikelets per panicle. The number of PB per panicle was not positively correlated with the number of spikelets on SB (secondary branches) per SB, and also was not positively correlated with the number of SB per PB. Since rice spikelets on PB generally produce fully filled grains, in contrast to spikelets on SB, we should be able to contrast genetically a rice panicle type which has a sufficient number of spikelets with high filled-grain percentage by increasing the number of PB and by suppressing the number of spikelets on SB.