Utilization of F_1 weakness gene for breeding of rice varieties which prevent gene pollution

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Recently, rice varieties having particular characteristics of color, fragrance, etc. awaken the interests of breeders to meet various needs other than staple food. Those traits, however, lower the grain quality when mixed with ordinary rice, and moreover those particular varieties often show "weedy" habit. The present project aimed at practical breeding of a red-rice variety which is good for coloring agent of alcohol but does not cause genetic contamination of ordinary rice fields.1) A number of red-rice varieties were evaluated regarding agronomic as well as chemical traits, and two were selected for breeding program. 2) A genetic system to cause inviability or weakness of F_1 hybrid was experted to work when ordinary rice plants arg naturally crossed with red rice. Since most Japanese cultivars carry one of the complementary F_1 weakness genes Hwc-2, introduction of another gene Hwc-1 into a selected red-rice variety "Soja" was carried out by backcrossing. 3) Monte Carlo computer simulation showed that this genetic system is effective for gene contamination through pollens, but not for gene contamination through seeds or plants. 4) In an attempt to discriminate pollens derived from different varieties in a pollen competition study, antibodies was obtained which have affinity to pollen polypeptides specific to red-rice "Soja". 5) Red-rice varieties are not necessarily weedy. F_2 study and selection experiment, however, indicated that weedy red rice could be segregated in the hybrid progeny between red and white non-weedy types, because two genes for red grain color are linked with two shattering genes, respectively, which work in a complementary manner.