16. A big-grain gene, Lk-f, found in a Japanese local variety "Fusayoshi" and its character expression

Institue for Agricultural and Biological Sciences, Okayama University, Kurashiki, 710 Japan

The grain size of rice is usually controlled by polygenes. As an exceptional case, a major gene controlling spikelet length was found in Japanese native variety, Fusayoshi. This variety had a kernel (brown rice) length of 6.8 mm (kernel weight being 32 mg), while othe Japanese varieties have a kernel length of about 5 mm (kernel weight 20-24 mg).

The mode of inheritance of grain size was studied in the F\2\ to F\5\ populations of crosses between Fusayoshi and several other normal-grained varieties. The F\2\'s segregated into 1 short : 2 medium (=F\1\) : 1 long grain classes, indicating that Fusayoshi had an incompletely dominant gene for long grain. The gene was symboled Lk-f tentatively. It was found to be linked with a gene for awn development, the recombination value being 7.4 to 8.4% and 7.6 +/- 0.57% in pooled data. Lk-f may be used as a marker.

Pairs of isogenic lines for the Lk-f/lk-f locus were established from heterozygous F\7\ lines of Shin 2 (normal) x Fusayoshi to examine the effects of the big-grain gene on yield component traits. In terms of Lk-f/lk-f ratios in various traits, the results were summarized as follows: