Abstract
A rice cultivar Shin 2 derived from a cross combination, Kameno-o 1×Kairyo Kikoku, develops notched grains with high percentage especially under low temperature condition, whereas their parental cultivars produce notched grains very little. Thus, Shin 2 canbe regalded as a transgressive type in respect of grain-notching. To clarify how the grain-notching line has been derived from the 'normal' parents is the main purpose of this study. The flrst experiment was performed using F2 and F3 plants of a Kameno-o 1×Kairyo Aikoku cross. After a preliminary test of F2 and F3 plants, a total of 918 F2 plants, and tneir parents and Fl plants as well, were investigated for notched grain frequency and caryopsis length in 1976. About a half of the F2 plants developed notchecl grains with a maximum frequency of 36%. The top and bottom 5% of the F2 population were selected for grain-notching, and the F3 lines were evaluated in 1977. Heritability value of the noched grain frequency estimatecl from the selcction response was 0.67. The hibohest mean value of notched grain frcquency was 39% in F3 lnes evaluated (Fig 1).
