Abstract
Two experiments were carried out to analyze the expression of some agronomic characteristics by semidwarfing gene sd-1, which has played an important role in improvement of rice productivity per area. A Japonica variety Norin 29, its semidwarf near-isogenic line SC-TN 1 and an Indica variety Taichung Native l were used as materials. SC-TN 1 was obtained by transfering the semidwarfing gene sd- 1 from Taichung Native 1 into a Japonica tall variety Norin 29. The results were as follows : (1) The culm length of Norin 29 was reduced by introducing semidwarfing gene sd-1. The elongation of lower internodes was promoted by high nitrogen level, depending on the variety : scarecely in the two semidwarf varieties, but substantially in Norin 29. The high lodging resistance of the semidwarf varieties seemed to be caused by the low response of lower internodes to nitrogen. (2) Semidwarfing of some agronomic characteristics. Bao-sen XIA., warfing gene sd-1 was found to have small negative pleiotropic effects for panicle length and l000 kernel weight. The negative effects may be recovered by genetic improvement. (3) The number of tillers and panicles of the two semidwarf varieties were larger than those of Norin 29 under high nitrogen level. The sd-1 gene was found to have positive pleiotropic effect on tillering ability.
