A new Japanese pear cultivar 'Osa Gold', resistant mutant to the black spot disease of Japanese pear (Pyrus pyrifolia Nakai) induced by chronic irradiation of gamma-rays

摘要

In 1986, young trees of Japanese pear cultivar Osanijisseiki were planted in the Gamma Field at 40-70 m (10 m intervals) distance from a 60Co source. In the summer of 1991, a mutant twig resistant to black spot (Alternaria alternata) was selected from a young tree at 40 meters from the 60Co source. This mutated twig (IRB 502 - 13 T) was grafted on rootstock outside of the Gamma Field, and was more resistant to the black spot disease after artificial inoculation than the original cultivar Osanijisseiki. Based on these results, IRB 502 - 13 T was designated as cultivar Osa Gold and registered as No5620 under the Seed and Seedling Law of Japan on 15 July, 1997. Osa Gold exhibits the same type of intermediate resistance to the black spot disease as the mutant Gold Nijisseiki. All other characteristics of Osa Gold are similar to those of the original cultivar Osanijisseiki.