STUDIES ON THE EVOLUTIONARY CHANGES IN YIELD AND RELATED CHARACTERS OF RICE CULTIVARS GROWN IN THE SOUTH-CHINA REGION

The evolutionary changes in yield and related characters of rice cultivars grown in the South-China region since 1950's were studied. 16 cultivars in early season and 17 in late season, representative of current and proceeded ones were planted in 1985, and were evoluated for grain yield and relatad morphological characters. It was shown by the SSR result that yield of rice in the South-China region were substantially increased over the last thirty years but no significant difference in yield among the current cultivars.In early ricet the yield components were developed from the panicle-weight type of the tall stature to the panicle-number type of the short stature in early 1960's, and to the impoved penicle-weight type of the current semi-dwarf cultivars. The cultivars with weighty panicles and more panicle numbers had been developed in late rice. There was no much impovement in weight of grain and fuil-grain percentage of the current cultivars both in the early and late rice The semi-dwarf cultivars with thicker base internodes and wall of stem were developed in early rice.Except the hybrid rice, the leaves size in canopy of the current cultivars were smaller and eracter in early rice but greater and eracter in late rice than those of the proceeded ones.Results from present studies suggest that further yield advances could be attained by combining higher biological yield and higher harvest index, greater grain numbers per pancile, higher full-grain percentage and higher weight of grain in rice breedlig programmes.