Abstract: Self-compatible pear cultivar 'Yan Zhuang' (Pyrus bretschneideri Rehd.) is recorded as bud mutant of self-imcompatible 'Ya Li'. The possible mutation was explored. Self-pollination experiments proves that 'Ya Li' is self-imcompatible (fruit set ratio of flowers 9.1%, no fertile seed) and 'Yan Zhuang' is self-compatible (fruit set ratio of flowers 56.9%, No. of seeds per fruit 8.64). Cross-pollination results suggested that the mutated gene is expressed in stylar of 'Yan Zhuang'. S-RNase gene has been reported as the key gene in style controlling self-incompatible mechanism. PCR with S-RNase gene sequence specific primers showed that the genotype of 'Ya Li' is S₂₁S₃₄, S₂₁ exits in all the 'Yan Zhuang' progenies by self-crossing. It seems that mutation of S₂₁-RNase gene results in the self-compatible phenotype of 'Yan Zhuang'. Western blot result showed that one of the two S-RNase brands in 'Yan Zhuang' disappeared in 'Ya Li'. So 'Yan Zhuang' pear probably results from S-RNase mutation of 'Ya Li'

Key words: pear, self-compatibility, S-RNase, molecular mechanism