Determination of S-genotypes of pear (Pyrus pyrifolia) cultivars by S-RNase sequencing and PCR-RFLP analyses.

The pear (Pyrus pyrifolia) has gametophytic self-incompatibility (GSI). To elucidate the S-genotypes of Korean-bred pear cultivars, whose parents are heterozygotes, the PCR amplification using S-RNase primers that are specific for each S-genotype was carried out in 15 Korean-bred pear cultivars and 5 Japanese-bred pear cultivars. The difference of the fragment length was shown in the following order: S6 (355 bp) < S7 (360 bp) < S1 (375 bp) < S4 (376 bp) < S3 and S5 (384 bp) < S8 (442 bp) < S9 (1,323 bp) < S2 (1,355 bp). We analyzed the sequence of the S-RNase gene, which had introns of various sizes in the hypervariable (HV) region between the adjacent exons with a fairly high homology. The sizes of the introns were as follows: S1 = 167 bp, S2 = 1,153 bp, S3 = 179 bp, S4 = 168 bp, S5 = 179 bp, S6 = 147 bp, S7 = 152 bp, S8 = 234 bp, S9 = 1,115 bp. There were five conservative and five hypervariable regions in the introns of S1, S3, S4, S5, S6 and S-RNases. A pairwise comparison of these introns of S-RNases revealed homologies as follows: 93.7% between S1- and S4-RNases, 93.3% between S3- and S5-RNases and 78.9% between S6- and S7-RNases. PCR-RFLP and S-RNases sequencing determined the S-genotypes of the pear cultivars. The S-genotypes were S4S9 for Shinkou, S3S9 for Niitaka, S3S5 for Housui, S1S5 for Kimizukawase, S1S8 for Ichiharawase, S3S5 for Mansoo, S3S4 for Shinil, S3S4 for Whangkeumbae, S3S5 for Sunhwang, S3S5 for Whasan, S3S5 for Mihwang, S5S? for Chengsilri, S3S5 for Gamro, S3S4 for Yeongsanbae, S3S4 for Wonhwang, S3S5 for Gamcheonbae, S3S5 for Danbae, S3S4 for Manpoong, S3S4 for Soowhangbae and S4S6 for Chuwhangbae. The information on the S-genotypes of pear cultivars will be used for the pollinizer selection and breeding program.