Analysis of varietal differences in self- and cross-incompatibility reactions of Japanese pears using stylar culture technique

Varietal differences of pollen tube growth among self-, cross-incompatible and cross-compatible pollinations were investigated by semi vitro assay usi ng detached styles in Japanese pear (Pyrus serotina Rehd. var. culta Rehd.) cultivars. Among the 52 self-compatible and -incompatible cultivars, the pollen tubes grew in considerably different ways. The percentages of styles with protrud ing pollen tubes from the basal cut end ranged from 0 to 47. Pollen tubes o f 'Shinsetsu', Nihonyamanashi, self- compatible 'Osa-Nijisseiki', and self -compatible strains obtained from 'Osa-Nijisseiki' grew well, and those of 'Okusankitsu', 'Yasato', 'Kikusui', 'Nijisseiki', and 'Kisui' did intermedi ately, whereas pollen tubes of 'Shinsui', 'Chojuro', 'Kimizukawase', 'Hohsu i','Kohsui', and 'Kohzo' grew poorly. Similar tendencies were observed when the number of pollen tubes protruding from the basal cut end among cultiva rs was counted. Generally, pollen tubes of cultivars derived from 'Nijissei ki' grew better than did those of 'Kohsui' and 'Shinsui', indicating that t he rate of pollen tube elongation of cultivars is a heritable character. In cross-incompatible and -compatible pollination combinations, the pollen tubes grew quite differently, depending on the parental combinations. The p ercentages of styles with protruding pollen tubes from the cut end ranged f rom 0 to 40 in cross-incompatible combinations, and from 26 to 97 in cross- compatible ones. By using excised styles shortened to 1/2 or 1/3 of the original length, the percentage of styles with protruding pollen tubes from the cut end improve d. The growth of self- and cross-incompatible pollen tubes became much bett er so that the promotion patterns were classified as follows: 1) tube elong ation becomes better as the style is shortened; 2) tube elongation becomes better but there are no differences between 1/2 and 1/3 reduction in style length; 3) pollen tube elongation becomes better only in the 1/3 style leng th, and 4) no change was found. These differences indicate that the inhibit ion of pollen tube growth occurs in different parts of the style among resp ective cultivars.