11. Endosperm mutants induced in two rice cultivars of Hokkaido

1) Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan

2) Kamikawa Branch, Hokkaido Agricultural Experiment Station, Asahikawa, 078-02 Japan

To obtain breeding materials for quality improvement, the seeds of two leading rice cultivars in Hokkaido, Shiokari and Yukihikari, were exposed to 20 kR of gamma rays. The M2 seeds of Shiokari were treated further with 0.2% solution of ethyl methanesulphonate. Amylose content in the endosperm of each M3 plant was measured with an autoanalyzer (Technicon Co.).

Mutants with different grain shapes and endosperm characters were detected in the M3 populatiens, 39 out of 1065 in Shiokari and 27 out of 885 in Yukihikari. In addition, four mutants with a low amylose content were found in Shiokari. Two mutants were selected from Shiokari. One had a transluent endosperm while the other showed a "dull" endosperm. The characteristics of several selected true-breeding lines are shown in Table 1. SM-2 had smaller grains with "dull" endosperm. Mutants were also selected from Yukihikari. YM-123 had a floury endosperm with high amylose content and an amylase activity five times as high as that of Yukihikari. YM- 146 was a big-grained mutant without white core and white belly, showing a superior milling quality. These promising mutants will be useful for genetic studies and for breeding programs to improve eating quality.