1) Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan
2) Kamikawa Agricultural Experiment Station, Asahikawa, 079 Japan
A long grain mutant N-173 was induced from the medium grain variety, Shiokari, by successive treatments with gamma rays and EMS. Its spikelet and grain lengths were 1.2 to 1.3 times as long as those of Shiokari, although its grain width and thickness remained unchanged (Table 1). Its 1000-grain weight was increased notably, reaching 29.2g while that of Shiokari is 21.2g. Line N-173 had elongated panicles and culms, its plant type shifting to a "panicle-weight type" from an intermediate type of Shiokari (Fig. 1).
Crossing experiments showed that a single gene with incomplete dominance
Table 1.Grain characters of N-173 (long grain mutant) and its original strain (A-136, Shiokari) ________________________________________________________________ Character Mutant Shiokari Ratio to Difference (N-173) (A-136) Shiokari _________________ mean t ________________________________________________________________ Spikelet length (mm) 7.70 6.19 1.24 1.51 7.14** Spikelet width (mm) 3.79 3.76 1.01 0.03 0.32 Grain length (mm) 6.44 5.01 1.29 1.43 9.31 Grain width (mm) 3.24 3.09 1.05 0.15 2.38* Grain thickness (mm) 2.29 2.24 1.02 0.05 0.88 Grain shape (length/width) 1.99 1.62 1.23 0.37 5.13** 1000-grain weight(g)29.2 21.2 1.38 8.0 ________________________________________________________________ *Significant at 5% level, **Significant at l% level.
was responsible for the long-grain character. As pleiotropic effects, the gene expressed an elongation of panicle and culm and a reduction in panicle number prominently. Line N-173 was crossed with Fusayoshi to examine if its long-grain gene was allelic to Lk-f carried by Fusayoshi. The F2 distribution of spikelet length appeared to be normal and transgressive toward greater length (Fig. 2), and no plant with the grain size of Shiokari (about 6 mm) occurred. This indicates that the induced long-grain gene is an allele at the Lk-f locus, being either identical to or an isoallele of Lk-f (cf. Takeda 1984; linkage group XI).
Fig. 3. Variations in spikelet length of F2 plants and F3 lines, which were
correlated significantly.
length, as the F2 plants and F3 lines derived from them showed a continuous variation in spikelet length and were correlated significantly (r=0.45, P<0.01; Fig. 3). Those minor genes would be involved in the differential genetic backgrounds of Shiokari and Fusayoshi, or induced by mutagenic treatments.
Reference
Takeda, K., 1984. A big-grain gene, Lk-f, found in a Japanese local variety "Fusayoshi" and its character expression. RGN 1: 108-109.