Rice Genetics-87
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Project Leader and Principal UC Investigators Neil Rutger, USDA-ARS |
Twelve
germplasm lines were released jointly with the California
Cooperative Rice Research Foundation, making them available to
other public and private rice breeders. The lines with improved stem
rot resistance and improved water weevil tolerance are among the
most useful in this release.Hybrid Rice Potential ExploredBasic research continues on genetic mechanisms that might make large-scale hybrid seed production easier. A study attempting to understand the behavior of a photosensitive genetic male sterile line of Calrose 76 identified last year produced inclusive results. Data seem to support the hypothesis that fertility is enhanced by short day length. However, a 16.7 percent seed set was noted under long day length conditions where little or no seed set was expected. Two new putative photosensitive male steriles were discovered from mutations of M-101 and M-201. Promising Sterile MaleWork with male sterile lines needed for natural crossing to produce hybrid rice focused on understanding the process of male sterility and identifying sterile lines with the best outcrossing properties. Current and previous studies have shown that male sterility is inherited as a single recessive gene character, but it was not known whether one or many different genes were involved. To date 47 of some 300 crosses between plants of different sterile sources have been evaluated. Many more of the crosses will have to be evaluated, but preliminary findings indicate that each male sterile gene is different. Thus, many different genes are probably involved in male sterility. Outcrossing studies have identified M-201 NP (no pollen) as a useful male sterile germplasm source for future studies. A radiation induced mutant of M-101 identified as a useful germplasm source in previous population improvement schemes also continued to show desirable characteristics. Resistance to Herbicides SoughtTissue culture and mutagenized seed selections for herbicide resistance are continuing. Two regenerated plants of M-202 that resulted from evaluating tissue cultures of 2,000 mature embryos of five rice varieties last year did not produce resistant progenies. Promising plants from mutagenized seed selections have been identified and will be grown to the flowering stage and crossed with M-102 and other tester strains to determine their inheritance of tolerance. Six surviving seedlings from a screening involving 200,000 M2 seeds are growing in the greenhouse, and their progeny will be tested for the level and inheritance of tolerance. Tissue Culture Studies Seek Breeding ImprovementsAnther culture, which could produce "instant" pure lines and shorten variety development cycles by two or three years is being explored. More than 28,000 anthers have been planted onto agar and, so far, 140 plants have been regenerated for further study and analysis. Another study is under way to compare mutants induced through the tissue culture process with those induced by radiation and chemicals. Asexual Seed Production SoughtDiscovery and successful application of apomixis, a form of asexual seed production, in rice would permit production of true-breeding F1 hybrids with permanent heterosis (increased vigor associated with crossbreeding). Twinning in seedlings can be an indicator of apomixis. Four highfrequency twinning lines from China show a rate of twinning ranging from six to 32 percent, compared with less than 0.1 percent twinning in ordinary rice. Studies are under way to determine exact origins of the twins and the inheritance of twinning.
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