Associations among characters related to yield sink capacity in space-planted rice

Yield sink capacity, a maximum size of sink organs to be harvested, has been one of the objectives in crop breeding for increasing yield. This study investigated associations among characters related to yield sink capacity of rice (Oryza sativa L.). Two populations of recombinant inbreds (RT), which differed in their genetic variance for grain size, were examined in four environments. Genetic and environmental correlations were estimated with an analysis of variance on the data obtained from single plants. Filled grain percentage showed a high negative genetic correlation with yield sink capacity in a RI population with smaller grain size variation (r = - 0.96). This correlation was not so high in another RI population with larger grain size variation (r = - 0.49). Hence, genetic variation in grain size could reduce the negative genetic relationship between filled grain percentage and yield sink capacity. In both RI populations, filled grain percentage showed negative genetic correlations with the traits for number of spikelets on secondary branches (SE) and a positive genetic correlation with number of primary branches (PB) per panicle. The number of PB per panicle did not show positive genetic correlations with the traits for number of spikelets on SE. These findings suggest that spikelets on PB, which generally produce well-ripened grains, can be increased by increasing the number of PB per panicle, without overproducing spikelets on SB. Thus, rice cultivars could be developed bearing panicles with both a large spikelet number and a high filled grain percentage.