title: Pollen factors controlling self-incompatibility strength in Japanese pear.
abstract: Japanese pear has a genetically controlled self-incompatibility system, but both the pollen-tube growth in a semi in vivo assay and fruit set after self-pollination differ considerably among cultivars. The percentage of styles in which pollen tubes have reached the base ranges from 0 to 36 %, a value determined by culture of styles in vitro, and fruit set ranges from 0.6 to 15.2 %. Based on these data, we have assigned a value for the self-incompatibility weakness to each cultivar. Here, we showed that pollen factors control the degree of self-incompatibility. When the pollen-tube growth of 13 cultivars was compared in a completely compatible 'Hougetsu' (S                 (1)                 S                 (7)) style, it differed a fair amount among cultivars and showed a significantly positive relation to self-incompatibility weakness (r = 0.707). The degree of self-incompatibility of pear is, therefore, determined by pollen factor(s) unrelated to the S-locus. Although the fruit set and fruit growth of 'Hougetsu' were not affected by the pollen donor, a positive relationship was also observed between seed number and self-incompatibility weakness (r = 0.972). However, in a style with no S-RNase production (genotype: S                                    (4)                             (sm)                                  S                                    (4)                             (sm)                 ), the relationship disappeared (r = 0.341) and pollen-tube growth was promoted by 12-36 % except in one cultivar. These results suggest that S-RNase functions as a cytotoxin on compatible pollen in a cultivar-dependent manner, and that the degree of inhibition is determined by pollen factor(s) unrelated to the S-locus. The pollen factor also functions on S-RNase in incompatible styles, resulting in a different degree of self-incompatibility.
authors.affiliation: Graduate School of Bioresources, Mie University, Tsu, Mie 514-8507, Japan. hiratuka@bio.mie-u.ac.jp
authors.forename: Shin
authors.initials: S
authors.lastname: Hiratsuka
authors.forename: Makoto
authors.initials: M
authors.lastname: Fujimura
authors.forename: Taishi
authors.initials: T
authors.lastname: Hayashida
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Nishikawa
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Nada
mesh_terms: D003433:Crosses, Genetic; D005638:Fruit / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D011058:Pollen / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D053205:Pollen Tube / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D054817:Pollination; D031989:Pyrus / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D012260:Ribonucleases / Q000378:metabolism*; D060436:Self-Incompatibility in Flowering Plants / Q000502:physiology*; D013045:Species Specificity
chemical_list: D012260:Ribonucleases; C022542:ribonuclease S