Progress in chestnut breeding at the Institute of Fruit Tree and Tea Science, NARO, Japan

Organized, government-funded chestnut (Castanea crenata Sieb. et Zucc.) breeding, has been conducted at the Institute of Fruit Tree and Tea Science, NARO, in Japan since 1947. The initial objective was to develop cultivars that ripen in the early or mid-season, that excel in yield, nut size, and nut quality by intra-specific cross of Japanese chestnut or interspecific cross between Japanese and Chinese chestnut. Serious damage from the chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu) (Dk) spread rapidly throughout Japan soon after the beginning of the program, and resistance to Dk was added as a goal of the program in 1952. By the early 1990s, six Japanese chestnut cultivars were released, including the currently leading cultivars, ‘Tanzawa’ (early-ripening), ‘Tsukuba’ (mid-ripening), and ‘Ishizuchi’ (late-ripening), that excel in yield, nut size, nut quality, and are resistant to Dk. With the successful establishment of Torymus sinensis, a parasitoid of Dk introduced from China, in the breeding field at NIFTS by the end of 1980s, the objective since the 1990s has been on improving nut quality by introducing genes from Chinese chestnut. ‘Shuuhou’ and ‘Mikuri’ have been released in this project. Furthermore, a simple method for evaluating the peeling pellicle ability was developed for breeding selection around the year 2000. Using this method, ‘Porotan,’ an easy peeling pellicle (EPP) cultivar of Japanese chestnut, was released in 2006. In addition, ‘Porosuke,’ which has EPP trait similar to ‘Porotan,’ and ripens one week earlier than ‘Porotan,’ was derived from the same cross as for ‘Porotan,’ and released in 2016. The current breeding objectives focus on breeding cultivars with good nut quality with EPP trait that ripen later than ‘Porotan’. To increase breeding efficiency, marker-assisted selection for easy peeling pellicle was performed in the 2010s. Furthermore, the development of DNA markers for other horticultural traits is currently in progress for future breeding.