Characteristics of Photosynthesis and Matter Partitioning in Leading Hybrid Rices, Oryza sativa L., Bred in China

The growth, photosynthesis and yield-determinants of hybrid rices were characterized here in comparison with a pure line cultivar. As experimental materials, leading three hybrids, Shanyou-6, Shanyou63 and Guangyou-6063, of China and a leading cultivar (pure line), Nipponbare, of Japan were used and grown outdoors in pots. The hybrids showed a vigorous growth and their grain yields (119.6 to 129.7 g/plant) were 40 to 50% higher than that (85.7 g/plant) of Nipponbare. A large leaf production and higher leaf photosynthetic rate were observed during the early half of the growth season in the three hybrids, both of which were main determinants to the substance accumulation in a plant. The culm+leaf weight of the hybrids increased to the maximum, then rapidly reduced during the maturing stage due to the substance translocation from culms or leaves to panicles. Vigorous development of root system was also a feature of these hybrids : the root weight of the hybrids being several times heavier than that of Nipponbare. The root weight reached the maximum just before or after heading, then decreased rapidly with maturing. It may be suggested that the roots of the hybrids function as a sink organ for substance accumulation before grain filling, and then it changes to a source organ exporting the accumulated substance to panicles during maturing stage