Reconsideration of S-genotype Assignments, and Discovery of a New Allele Based on S-RNase PCR-RFLPs in Japanese Pear Cultivars.

The S-genotype assignments in the Japanese pear cultivars, ‘Akaho’, ‘Tanzawa’, ‘Kimizukawase’, ‘Choju’, ‘Ichiharawase’ and ‘Meigetsu’ previously determined by pollination tests have raised some doubt recently. These cultivars were analyzed by S-RNase based PCR-RFLP, and their S-genotype assignments reconsidered. The assignment based on the PCR-RFLP system was in agreement with that determined previously by pollination tests in six cultivars, ‘Chojuro’, ‘Doitsu’, ‘Kikusui’, ‘Kosui’, ‘Taihaku’ and ‘Yakumo’, confirming the applicability of the system. ‘Akaho’, ‘Tanzawa’, ‘Kimizukawase’ and ‘Choju’ were analyzed and assigned as S3S5, S4S5, S1S5 and S1S5, respectively. Two of these cultivars, ‘Akaho’ and ‘Tanzawa’, were also confirmed by our pollination tests. In three cultivars, ‘Ichiharawase’, ‘Meigetsu’ and ‘Heiwa’ (‘Nijisseiki’בIchiharawase’), a new S-RNase fragment with a size and digestion pattern distinct from those of S1 to S7-RNases of Japanese pear was amplified. The deduced amino acid sequence in the hypervariable region of this S-RNase was quite different from those of S1 to S7-RNases. We, therefore, assigned this S-RNase as S8-RNase, and identified the S-genotypes of ‘Ichiharawase’, ‘Meigetsu’ and ‘Heiwa’ as S1S8, S1S8 and S4S8, respectively.