Male Sterile Mutants from Rice Somaclones

Abstract

The total area of hybrid rice plantation was more than 11 million ha in 1988 and the yield of hybrid rice made up 50% of the total yield of rice production in China (Yuan 1988). The per hectare yield in hybrid rice was 6.6 ton average and 25% higher than that in conventional varieties. The utilization of heterosis in rice has been a great success, with huge economic and social benefits in China (Yuan 1986). However, more than 90% of the mother parents of the hybrid rice (combination) which were used in hybrid rice production are derived from the same male sterile cytoplasmic source, i.e., WA-type (wild rice abortive type) ms-cytoplasm. It is well known that the extensive use of a single source of cytoplasm of hybrid maize in the whole hybrid maize area of USA caused the wide spread of spot disease of corn (Helminthosporium maydis), resulting in heavy loss in maize production in America. Although a direct relationship between the WA-type cytoplasm and susceptibility to a major disease or insect in rice has not been established so far, the extensive use of a single source of male sterile cytoplasm may cause the hybrid rice to be vulnerable to a disease or insect epidemic (Virmani et al. 1986) and also limited the breeding and selection of stronger and better combinations of hybrid rice. Meanwhile some shortcomings can be found in WA-type cytoplasm such as poor disease/insect resistance and low quality. Therefore, the new cytoplasmic male sterile (CMS) lines with non-WA cytoplasm have been studied and developed for a long time. Besides the conventional methods of establishing CMS lines, which include backcrossing (intra- and interspecific crossing) and mutagenic induction