Effects of Ssil gene controlling dm-type internode elongation pattern on lodging resistance and panicle characters in rice

The dm-type semi-dwarf mutant DMF-1 is controlled by the semi-dominant gene, Short second internode 1 (Ssi1), located in the region within ca. 20 cM on the long arm of chromosome 1. In order to elucidate the function of this gene in relation to the lodging resistance and panicle characters in various genetic backgrounds, these agronomic characters were investigated by using DMF-1, Reimei (sd1 allele), six different Fsub(10) lines (DML-1 to -6) with homozygous form of Ssi1, and their parents. The experimental results showed that all the dm-type lines except for DML-6 (DMF-1 x Tan-Ginbozu) whose genotype belonged to the homozygous form of both Ssi1 and d35, significantly increased the lodging resistance, compared to their respective parents. On the other hand, although DMF-1 reduced seed production because of the high ratio of appearance of hull-cracked kernels, such a negative character had been improved in DML-1 (Kinmaze x DMF-1), DML-2 (Nipponbare x DMF-1) and DML-4 (Sasanishiki x DMF-1). Principal component analysis based on fifteen panicle characters also showed that these three Fsub(10) lines should be assigned to a group of normal cultivars. These results suggested that it was possible to develop a new semi-dwarf variety for practical use, expressing a high level of lodging resistance associated with the Ssi1 gene in various genetic backgrounds.