A Self-compatible Pollen-part Mutant of Japanese Pear Produced by Crossing ‘Kosui’ with Pollen from Gamma-irradiated ‘Kosui’

The self-incompatible (SI) Japanese pear cultivar ‘Kosui’ was pollinated with pollen collected from a chronically gamma-irradiated ‘Kosui’ tree, and a progeny was obtained. This progeny resulted in the identification of self-compatible (SC) breeding selection, designated 415-1, which showed 74.4% fruit set in a self-pollination test. PCR-based genetic analysis revealed that 415-1 has S-RNase genotype S4S5, which is the same as that of the parent, ‘Kosui’. Pollination trials were used to investigate whether 415-1 harbors a stylar-part mutation or a pollen-part mutation in its SI locus. When 415-1 was pollinated with pollen from cultivars of the same genotype (‘Syuugyoku’ and ‘Oushuu’), no seed-containing fruit were set, indicating that 415-1 contains functional S4- and S5-RNase alleles. On the other hand, when ‘Syuugyoku’ and ‘Oushuu’ were pollinated with pollen from 415-1, fruit-bearing seeds were produced; therefore, we conclude that 415-1 carries a pollen-part mutation at the SI locus. This new self-compatible breeding selection will be useful for the development of new Japanese pear cultivars with SC.