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

Abstract

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.