Horticultural utilization of self-incompatibility gene and its products in the Japanese pear.

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Results on relationships between self-incompatibility expression and S-RNase concentrations in the style of Japanese pear cultivars were summarized and presented at "The International Symposium on Asian Pears" held in the summer of 2001. The content of the Symposium is in press as a review in Acta Horticulturae, and detailed data are in press in Sci. Hort.S-RNase was purified from pear styles and subjected to pollen assay in vitro ; S-RNase selectively inhibited the incompatible pollen germination and tube growth, and the inhibition was dose-dependent. These results support the hypothesis described above that cultivar difference in self-incompatibility expression is regulated by the S-RNase concentration in the style of each cultivar.Specific amplification of S_<1->, S_<2->, S_<4->, and S_5-gene fragments was succeeded. By using this technique, S-genotypes of several cultivars were re-examined, and plants with new S-genotypes were identified in F_1 plants produced in our laboratory. These results were published in J. Japan. Soc. Hort. Sci. Meanwhile, S_2-gene fragment was used as a probe and S_2-gene expression was compared among several cultivars possessing S_2-gene. Gene expression was considerably different among the cultivars, and the difference seemed parallel with S_2-RNase concentration in each cultivar. These results suggest that cultivar differences in self-incompatibility expression are due to different expression of S-gene in respective cultivars.