Estimation of the Proportion of Offspring with Ripening Time Genotypic Values Exceeding a Given Critical Selection Value in Japanese Pear Cross-breeding

Abstract

Six offspring in each of 24 families and their parents in Japanese pear were evaluated regarding the fruit ripening time. Analysis of variance for the offspring, which estimated between- and within-family variance, and the regression of the mean value in a full-sib family on the mid-parental value (MP) revealed that the genetic differences among families could be explained mostly by MP, indicating that they were under additive genetic control. Genotypic values of offspring in a family were assumed to be normally distributed around the regression line with the sum of within-family genetic variance and the variance due to the deviation of the family-mean from the regression line. Based on the parental mean performance of 10 fruit on a single tree for six years, the coefficient of regression of mean values in a full-sib family on MP was 0.8072 ± 0.02 (SE), and the proportion of offspring with genotypic values leading to ripening earlier than middle-August was estimated at 7 and 0.7% for the two sets in the case of MP = 2.7 and 3.55, respectively.