Inbreeding Coefficient and Mid-parental Value (MP) Can be Used to Estimate Family-mean of Fruit-weight of Offspring in Crossbreeding Test

Abstract

Six offspring in each of 26 families and their parents in Japanese pear were evaluated regarding the fruit weight. Analysis of variance of the offspring, which estimated the between- and within-family variance, and multiple-regression of the mean value in a full-sib family with the mid-parental value (MP) and inbreeding coefficient (F) revealed that the genetic differences among families could be explained mostly by MP and F. Genotypic values of offspring in a family were assumed to be normally distributed around the multiple-regression line with the sum of within-family genetic variance and variance due to the deviation of the family-mean from the multiple-regression line. Based on the parental mean performance of 10 fruits on a single tree for five years, the coefficients of multiple-regression of mean values in a full-sib family on MP and F were 0.6263 ± 0.13 and –0.7343 ± 0.20, respectively, and the proportion of offspring with genotypic values and a fruit weight > 350 g was estimated as 23.6 and 1.3% for 0.104 and 0.3438 F values, respectively, in individuals from a cross with MP = 300 g.