Dominant Gene, Ssi1 Expresses Semidwarfism by Inhibiting the Second Internode Elongation in Rice.

Abstract

A dm-type rice mutant DMF-1, which was induced by X-ray irradiation of plants of the rice cultivar Fujiminori (Yamaguchi 1976), showed semidwarfism with an apparently normal growth except for the inhibition of elongation of the 2nd internode. This mutant character was found to be controlled by a dominant gene Ssi1 (short second internode 1)(Wu et al.1997b). The culm of DMF-1 (65.2cm) was significantly shorter than that of Fujiminori (82.1cm) and the semidwarf cultivar Reimei (70.4cm). The F1 reciprocal hybrids between DMF-1 and Fujiminori tended to show an intermediate culm length between that of their parents. There were no significant differences in agronomic characters such as panicle length and panicle number among the F1 reciprocal hybrids and their parents. The expressivity of the dm-type (EDM), represented by the percentage of the number of dm-type culms to the total number of culms per plant, was estimated in the F1 and F2 from the reciprocal crosses between DMF-1 and Fujiminori. The Ssi1Ssi1 plants exhibited 100% or nearly 100% EDM in all the different cropping seasons. However, in the Ssi1+plants EDM was unstable even in the same season. Therefore, it was assumed that DMF-1 was controlled by an incompletely dominant gene Ssi1. Results of linkage analysis using two morphological marker genes showed that Ssi1 could be located between rl4 (rolled leaf 4) and shr1 (shrunken endosperm 1) on chromosome 1 with recombination values of 10.4 and 10.1%, respectively.