INHERITANCE OF RIPENING TIME OF FRUIT OF JAPANESE PEAR (PYRUS-PYRIFOLIA NAKAI)

Inheritance of ripening time of Japanese pear was investigated using twenty full-sib families. Frequency distribution in each family could be approximated to normal distribution, indicating that this character was inherited polygenically (Fig. 1). Significant regression coefficients and correlation coefficients were obtained-between mid-parent and offspring; the regression was in the range of 0.867 approximately 1.045, the correlation being 0.916 approximately 0.985 (Table 3). Both regression coefficients and correlation coefficients, obtained between mid-parent and offspring in the full-sib population, are generally recognized as valuable genetic parameters. Especially, the regression. of offspring on mid-parent in the random mating population is expected to be equal to the estimate of the heritability. Therefore the heritability on ripening time is considered to be extremely high (Table 3). Variance analysis indicated that variances between and within family were significant. Variances due to year and interaction between family and year were not significant (Table 7). The ratios of variance due to family, year, interaction between family and year, individual and error to the total variance were estimated to be 0.341, 0.003, 0.005, 0.612 and 0.039 respectively. Among the ratios of variance component, those due to family and individual were both high (Table 8). It is concluded that ripening time in Japanese pear population has a heritability as high as 0.95 (Table 3), and environmental variance of this character is relatively small(Table 8).