Image analysis of fruit deformation and its application to breeding in Japanese pear (Pyrus pyrifolia (Burm. f.) Nakai)

Shape is one of the most important factors in determining the appearance quality of a fruit. In Japanese pear (Pyrus pyrifolia (Burm. f.) Nakai), fruit deformation often occurs and damages the fruit appearance, highlighting the need for breeding improvements. Therefore, this study aimed at developing an image analysis method for objectively identifying deformed fruits and applying the method to Japanese pear breeding. We used 1595 fruit images from 22 cultivars and 551 F₁ individuals from 44 cross combinations, which were produced by a Japanese pear breeding program. From these images, we measured four shape parameters to evaluate fruit deformation, and subsequently distinguished between normal and deformed fruits by using these parameters. Based on a binary classification of normal vs. deformed fruits, we estimated the narrow-sense heritability of fruit deformation rate as 0.34. We predicted genotypic values of fruit deformation rate as being in the range of 0.030 to 0.625. Our results demonstrate that (1) the image analysis method used in this study can effectively distinguish between normal and deformed fruits, (2) there is significant genetic variation in fruit deformation rate in Japanese pear breeding materials, and (3) fruit deformation rate is a trait that can be genetically improved. These findings can contribute to the efficient development of pear cultivars with superior appearance quality.