Studies on varietal difference in yielding ability in rice - Relationship between source-sink ratio and yield

The yielding abilities of rice varieties were examined among three groups: 10 European and American varieties (E group), 20 Japanese varieties (J grou p), and 16 high-yielding varieties bred in Asian countries (H group). Each yield capacity (NV) was expressed as a product of the number (N) and the vo lume (V) of unhulled rice. The yield contents (CW+Delta W) were expressed b y the sum of reserved carbohydrates in the rice plant at the full heading d ate (CW) and the dry matter production amount during the ripening period (D elta W). The (CW+ Delta W)/NV was regarded as the source-sink ratio. The av erage yield (Y) was highest in H group and lowest in E group. Both NV and C W+Delta W of H group were highest among the three groups. But Delta W of H group was not so large in comparison with that of J group. The (CW+Delta W) /NV of H group was lower than that of J group because the increase of NV w as greater than that of CW+Delta W in H group. The transfer ratio of yield contents [Ef: Y/(CW+Delta W)] was highest in H group. The specific gravity of unhulled rice (S:Y/NV) of H group was as high as that of J group. These results suggest that the high yielding ability of H group is mainly attribu table to its large NV and CW, and also to its high Ef. Consequently, it is considered that an enhancement of source-sink ratio with the increment of D elta W is necessary to improve the yield potential in H group.