A GENETIC-ANALYSIS OF LOW-TEMPERATURE-SENSITIVE STERILITY IN INDICA-JAPONICA RICE HYBRIDS

Low-temperature-sensitive sterility has become one of the major obstac les in indica-japonica hybrid rice breeding. The objectives of this pa per were to evaluate the extent of the fertility reduction and to dete rmine the genetic basis of low-temperature-sensitive sterility. Sevent een varieties were crossed in various ways to produce 21 F(1)s includi ng 16 indica-japonica hybrids. Fertility of the F(1)s and their parent s was examined under both high and low temperature conditions. Conside rable reduction in spikelet fertility was observed under low-temperatu re conditions in the majority of the indica-japonica hybrids having at least one wide compatibility parent. However, the extent of fertility reduction varied greatly, depending on the parental genotypes. Data f rom five pairs of reciprocal crosses indicated that the cytoplasm had no effect on fertility reduction. The more-or-less bimodal distributio n of the fertility segregation of one BC1F1 and two F-2 populations un der low-temperature conditions suggested that the low-temperature-sens itive sterility was controlled by only one or a few genes. It was also shown that the low-temperature-sensitivity is not related to wide com patibility. We conclude that it is possible to develop indica-japonica hybrids with wide compatibility and also insensitivity to the low-tem perature conditions.