Correlation of Emergence with the Lengths of Mesocotyl and Lower Internodes in Rice Seedlings under Deep Sowing Condition

Abstract

The objective of this study was to obtain basic knowledge about the breeding of deep-sowing-tolerant varieties suitable for direct sowing cultivation by using 50 Japanese rice varieties sown at the depth of 7 cm. A significant difference among varieties was observed in the emergence percentage, ranging from 94% to 0% (average 59%). Average emergence days ranged from 18.8 to 11.4 days (average 15.6 days), and the emergence coefficient ranged from 7.19 to 0.56 (average 4.04). A significant difference among varieties was observed in both the average emergence days and the emergence coefficient. The emergence coefficient showed a significant positive correlation with the emergence percentage, and significant negative correlation with the average emergence days, but the emergence percentage was not significantly correlated with the average emergence days. Significant differences among varieties were also observed in the starting time of emergence and the increasing exponents of emergence percentage obtained from the regression equation between the days after sowing and emergence percentage. Multiple regression analysis was conducted with the starting time of emergence and the increasing exponents of emergence percentage as the explanatory variable, the emergence percentage and the average emergence days as the objective variable. Thus, the results demonstrated that the contribution ratio of the starting time of emergence to the increasing exponents of emergence percentage for the emergence percentage was 25: 75, and that to the average emergence days was 92: 8. The results of the multiple regression analyses with the mesocotyl length (ML), the first internode length (I L) and the second internode length (II L) as the explanatory variables, and the starting time of emergence, the increasing exponents of emergence percentage and the emergence percentage as the objective variables, was that the contribution ratio of ML, I L and II L to the starting time of emergence was 56: 40: 4, that to the increasing exponents of emergence percentage was 18: 32: 50, and that to the emergence percentage was 6: 40: 54. From these results, the most important characteristic in the deep-sowing tolerance breeding of Japanese varieties was considered to be the second internode length followed by the first internode length. The contribution of the mesocotyl length was considered small in this experiment.