Determining S-genotypes of two sweet cherry (Prunus avium L.) cultivars, 'Takasago (Rockport bigarreau)' and 'Hinode (Early purple)'

Abstract

'Takasago (Rockport Bigarreau)', one of the major early ripening cultivars of sweet cherry in Japan, was reported to be cross-incompatible with 'Hinode (Early Purple)'. Thus, they were assumed to have the same S-alleles, although their S-genotypes were unknown. However, when 'Takasago' was cross-pollinated with 'Hinode' at the Yamagata Prefectural Horticultural Experiment Station, the fruit set normally (unpublished data), which suggests that they are cross-compatible. In this study, we re-evaluated crossability between the two cultivars by controlled pollination tests and determined their S-genotypes by the molecular typing system recently developed for S-alleles of sweet cherry. The cross-pollination tests conducted at two different locations in Japan showed that 'Takasago' and 'Hinode' were self-incompatible but reciprocally cross-compatible. Furthermore, 2D-PAGE (two dimentional-polyacrylamide gel electrophoresis) analysis for stylar extracts revealed that they have none of the common S-RNases, S-gene products in styles of sweet cherry, which suggests that their S-genotypes are completely different. By S-RNase spot patterns in 2D-PAGE profiles and RFLP (restriction fragment length polymorphism) analysis, S-genotypes of 'Takasago' and 'Hinode' were proposed to be S1 S6 and S 2S(x) (S(x) is a novel S-allele different from S1 to S6), respectively. This implies that 'Hinode' is cross-compatible with all cultivars of known S-genotypes. The usefulness of biochemical and molecular methods for S-allele typing employed in this study is discussed.