Abstract:

Pyrus pyrifolia is a commercially important fruit tree which exhibits gametophytic selfincompatibility (GSI). It is necessary to identify S genotypes of cultivars for determination of crosscompatible combination prior to performing pear plantation and breeding programs. In this study, seven cultivars of P. pyrifolia were used for S genotype analysis by PCRbased molecular method with primers designed from conserved sequences of known pear S RNases. Amplified products were analyzed by 1.8% agarose gel electrophoresis. In each of the four cultivars `Chubixiang', `Huangpishui', `Zhenghedaxueli' and `Hongtaiyang', two expected bands were generated. The amplified products in the other three cultivars did not show length polymorphism, and therefore were further separated by 6% polyacrylamide gel electrophoresis (PAGE). A total of 14 purified fragments from the seven cultivars were cloned and sequenced. Sequence analysis revealed that 10 alleles with typical structural features of pear S RNase were identified, of which one from `Zhenghedaxueli', with 494 bp, was determined as a new SRNase allele that was tentatively denominated as S 43 RNase (GenBank accession No.EF566873). RTPCR revealed that the S43RNase was expressed specifically in the styles, which is consistent with the expression pattern of S RNases. Comparison of genomic and cDNA sequences revealed there was an intron of 294 bp in the S43RNase gene. The deduced amino acid sequence shared 65% to 92% similarity with other Maloideae S RNases. This study will be helpful in pear production and breeding programs.

Key words: Pyrus pyrifolia, gametophytic selfincompatibility (GSI), PCR, S genotype, S RNase