Breeding, genetics, and genomics of fruit trees

Because most regions of Japan are in the temperate climate zone, many deciduous and evergreen fruit crops are cultivated in Japan. In addition to fruit cultivation in the temperate zone, some southern areas, such as the Ryukyu Islands that stretch from Kyushu to Taiwan, are at the northern limits for tropical fruit production without the need of artificial heating. At present, annual fruit production in Japan (in billion yen) is as follows: citrus (Citrus spp. comosus) and loquat (Eriobotrya japonica) are also economically important fruit species. Pineapple, mango, and papaya (Carica papaya) are major tropical fruits cultivated in the southern area of Japan. Hundreds of new elite fruit tree cultivars have been bred and propagated over more than 100 years after modern cross-breeding practices were adopted in Japan. The 'Fuji' apple, 'Kyoho' and 'Shine Muscat' grape, and 'Kosui' and 'Hosui' Japanese pear cultivars are among the most representative cultivars bred in Japan. Because the fruit characteristics of cultivars principally bred in Japan are rather different from those bred outside of East Asian countries, many breeders and scientists throughout the world are interested in the breeding history of Japanese cultivars. Of note, special interest is paid to the breeding history of extremely high fruit quality cultivars, one of the most important characteristics. In citrus, the primary objectives in breeding programs have been improving the satsuma mandarin to further increase fruit quality, fragrance, and stable production. 'Kiyomi' was bred in 1979, originating from a hybrid between the most popular satsuma mandarin cultivar 'Miyagawa wase' and the sweet orange 'Trovita'. 'Kiyomi' and its progeny cultivars 'Shiranuhi', 'Harumi', 'Setoka', and 'Harehime' have been replacing the cultivation of mid-late ripening citrus varieties. The number of Japanese apple cultivars is estimated to be approximately 300, including 185 original cultivars regis-and 'Shinano Gold' are major cultivars with excellent eating quality. The table grape breeding programs have combined the berry quality of V. vinifera with the ease of cultivation of V. labruscana by an interspecific crossing approach, resulting in the new excellent cultivars 'Neo Muscat', 'Kyoho', 'Muscat Bailey A', and the very recently developed 'Shine Muscat'. The current Japanese pear breeding objectives mainly focus on combining superior fruit quality with multiple disease resistance (resistance to pear scab and black spot diseases) and self-compatibility, in order to breed new cultivars superior to the present major cultivars 'Kosui' and 'Hosui'. In oriental persimmon breeding, pollination-constant non-astringent (PCNA) cultivars are the …