Cold Tolerance in Rice Plants with Special Reference to the Floral Characters : II. Relations between Floral Characters and the Degree of Cold Tolerance in Segregating Generations

Abstract

Relations between fioral characters and the degree of cold tolerance were studied in segregating generations of the hybrid between the varieties, Kinmaze and Somewake. A cold sensitive variety Kinmaze has short anthers and short stigmas. On the contrary, an extremely cold tolerant Japanese local variety Somewake has long anthers and long stigmas. The following two methods were adopted in this experiment ; ( 1 ) Anther and stigma lengths of F2 plants were measured at the heading time. To estimate the degree of cold tolerance, Iow temperature treatment (17°C day, 12°C night) was conducted on the suc-ceeding F3 Iines for five days at the meiotic stage using phytotron. ( 2 ) Genetically identical varieties were obtained by dividing F2 seedlings into three plants with a razor at the early tillering stage. As shown in Fig. 1, one of them was grown under natural conditions as a control, another one was placed under low temperature L0r five days at the meiotic stage and the third one was fixed in F.A.A. for measurement of fioral characters at the heading. Prior to analysis, seed sterility percentages (degree of cold tolerance) were transformed to angles as follows : sterility index=arcsiri√(percent of sterility), Characters recorded in each method were statistically analyzed. In method ( 1 ) anther length in F2 negatively correlated with sterility index (Fig. 2). In method (2) both lengths of anther and stigma negatively correlated with sterility index (Fig.5 and Fig.6). Moreover there were significant correlations between the product of anther and stigma lengths and sterility index in both methods (Fig.4 and Fig.7). The multiple regression analysis based on I84 observations in F2 yielded the following equation :y = 122. 944- 17. 462 x1 -45. 877 x2 where x1 : anther length, x2 : stigma length, y : steruty index. By uslng the above multiple regression equation, contribution was calculated (R2=0. 3449). It was sugested from these results that the plants with long anthers and/or long stigmas were cold tolerant and these floral characters could be useful as the selection criteria in the process of rice breeding aimed for cold tolerant varieties.