Abstract
We divided the developmental processes from microspore differentiation to fertilization into 4 phases and defined the component relating to fertilization in each phase. The percentage of fertilization was expressed by the product of the 4 components which are the number of differentiated microspores (X1), the percentage of developed pollen grains (X2), the percentage of shed pollen grains (X3) and the fertilization efficiency of shed pollen grains (X4). There were greate varietal differences in the percentage of fertilization and the contribution degrees of these components to fertilization. The contribution ratio of these components to fertilization was estimated by multiple regression analysis, using 19 rice varieties differing in cooling tolerance. The first 3 components (X1, X2 and X3) explaind 82% of the variation among the varieties in the percentage of fertilization of spikelets cooled at the critical stage. The 4th component, which is the product of the percentage of pollen germination on the stigma and the fertilization efficiency of germinated pollen grains, was not estimated in this paper. Somewake, Akage, Kitaake, Dohokumochi 18, Chubo 42 and Hayayuki are expected as donors with high capacity for X1, Somewake, Hamaasahi, Kitaake, Todorokiwase, Hayayuki and Kochiminori as donors with high capacity for X2, and Sorachi, Chubo 42, Hayayuki and Kitaake as donors with high capacity for X3. The concept of fertilization-components is useful as tools to indentify genetic sources and donors of cooling tolerance, and to analyse physiological mechanisms of cooling tolerance.
