9.Studies on crossability between two cultivated rice species Oryza sativa and O. glaberrima
 D. TAO, F. HU, Y. YANG, Y. ZHOU and H. CHEN

Food Crops Research Institute, Yunnan Academy of Agricultural Sciences, Kunming 650205, The People's Republic of China

Rice is the staple food for the world and two rice species are cultivated for food production. Oryza sativa originated in Asia but is widely grown. O. glaberrima originated and is cultivated in West Africa. Both species have same genome AA (Chang, 1976; Morinaga et al., 1957). The high sterility of interspecific hybrids is a serious reproductive barrier (Jones et al., 1997; Morinaga et al., 1957; Morishima et al., 1962, 1963; Sano et al., 1979; Sano, 1983; Tao et al., 1997). Regarding crossability, there is no consensus. Morinaga et al. (1957) and Morishima et al. (1962, 1963) thought that there was no crossing barrier between the two species. Chu et al. (1969) thought also so. The intraspecific hybridization rate was 51% in O. sativa and 62% in O. glaberrima, whereas the interspecific hybridization rate was 39-42%. An extreme example was reported by Jones et al. (1997): from 48 interspecific crosses, only 7 crosses were successful in seed production. Great differences in interspecific crossability were found between different years by Sano et al. (1979), and before BC3, the cytoplasm played an important role in crossability. Tao et al. (1997) reported that when O. glaberrima was used as maternal parent, higher crossability could be achieved.

Our further studies (Tao et al., 1999) from 1997 to 1998 indicated that, interspecific crossability of O. sativa and O. glaberrima was between the intraspecific hybridization rates of the two species. The latter value was 68.2% to 95.2% for O. sativa, and there was great variation in different seasons (Table 1).

In order to study the factors influencing interspecific crossability, crosses were made in the early season (March-June) of 1998 in Hainan. Three japonica (IRAT104, Mengwanggu, Reimei), one indica (Guichao 2), and five accessions of O. glaberrima (IRGC101942, IRGC103648, IRGC102205, IRGC102277, IRGC102502) were used to make 40 interspecific crosses between O. sativa and O. glaberrima, 6 intersubspecific crosses between japonica and indica, and 6 intraspecific crosses in O. glaberrima. In the winter season (October-March), 1998, the experiment was repeated. Variance analysis indicates that season, genotype of O. sativa, genotype of O. glaberrima, and cytoplasm were significant or highly significant factors for interspecific crossability. All interactions were not significant, whether the model was fixed or free. The F value of season was the biggest, followed by cytoplasm, genotype of O. sativa, and genotype of O. glaberrima (Table 2) Thus, interspecific crossability was a partial barrier, affected by environment (season), cytoplasm, genotype of O. sativa, and genotype of O. glaberrima.

Ladizinsky (1992) classified crossability into both cross-directions complete, successful unilateral, partially successful, and incompatible four kinds. From the above results, interspecific crossability between two cultivated rice species is partially incompatible, and partially


This study was supported in part by Yunnan Natural Science Foundation and West Africa Rice Development Association (WARDA).


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