POTENTIAL OF BREEDING MALE STERILES AT HIGH LEVELS OF OUTCROSSING

This paper deals mainly with the following:1.the important traits influencing the outcrossing of male steriles(MS) in rice;2.the genetic variability and inheritance of the floral traits; 3.the correlations between the floral traits, and between the floraltraits and the outcrossing of MS; 4.the approach and prospect of breeding MS lines at high levelsof outcrossing.Compared with wild rice, MS lines have some characters favourable to outcrossing, such as complete male sterile, longer duration of spikelet opening; MS lines also have a few unfavourable factors, for instance, lower stigma exsertion, smaller size of stigmas, late flowering,incomplete exsered panicles, cleistogamy.The characters mentioned above are inherited. In general, the traits related to floral structure have greater heritability than those related to flowering behaviour. The latter traits are greatly affected by environmental factors.The genetic differences in the floraltr aits are apparent.The desirable floral plasm exists mainly in wild rice, and also in cultivars.There have not yet been reported the genetic effects of the floral traits on the outcrossing of male steriles and their relative importance. Marked phenotypic correlation has been found between outcrossing and stigma exsertion.The correlation between floral traits are also significant. Discussions have been made on the identification,peculiarity and possible utilization of four special materiales-multi-stigmas, unclosedspikelets after opening,two flowering peaks a day and long panicle necks (eui) .The paper concludes that the program of breeding male steriles at high levels of outerossing by improving the floral traits, especially pistil characters is feasible.