Relationship between inbreeding coefficients and plant height of 1-year-old seedlings in crosses among Japanese pear (Pyrus pyrifolia Nakai) cultivars/selections

Plant height, a vigor trait, in 1-year-old seedlings made from Japanese pear (Pyrus pyrifolia) cultivars/selections was measured using 994 individuals from 29 families. The family mean of plant height was negatively correlated (r=−0.72**) to the inbreeding coefficients (F). The regression of the family mean (Fm) on the F value (Fm=130−104F) showed that inbreeding depressions were 8%, 20%, and 40% for F=0.1, 0.25, and 0.5, respectively. According to the regression, the family mean at F=0 was estimated at 130cm. These results showed that the vigor was greatly influenced by inbreeding in Japanese pear. Within-family variances, the genetic segregation of offspring in a family, differed according to family. The proportions of offspring with plant height above 130cm (estimated Fm for F=0) were extremely low, i.e., 0–17% for 0.5≤F<0.60 and 0–8% for F=0.75.