Abstract
The percentage of ripened grains (R) and specific gravity of winnowed rough rice (S) were compared among 25 rice varieties to analyze the varietal differences of ripening ability. The relationship between the R (Y axis) and the accumulated average air temperature during the ripening period T (X axis) was shown by the following formula :
Y=00—a · exp (—b · X)
The constant b and the intercept of X axis were different among varieties. The constant b×105 (ripening index, RI) showed a significant positive correlation with R, and the intercept of X axis (starting temperature of ripening, ∑Ts) showed a significant negative correlation with S. Yield content was shown as the sum of reserve carbohydrate (C) and dry matter produced after heading (ΔW) ,and yield capacity as the product of the number of rough rice (N) and volume of winnowed rough rice (V). Then, the correlation of (C+ΔW) /NV with RI and ∑Ts was examined. (C+ΔW) /NV showed a significant positive correlation with RI. The variety with a large C value has a tendency to have a low ∑Ts. These results imply that the cultivar with a high yield content / yield capacity ratio has a higher percentage of ripened grains because its ripening index is high. Also the cultivar with massive reserve carbohydrate was considered to start ripening earlier increasing the specific gravity of winnowed rough rice.
