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
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).
Chang T. T., 1976. The origin, evolution, cultivation, dissemination, and
diversification of Asian and African rices. Euphytica, 25: 425-441.
Chu, Y. E., H., Morishima, and H. I. Oka, 1969. Reproductive barriers distributed
incultivated rice species and their wild relatives. Jap. J. of Genetics, 44:
Jones M. P., M. Dingkuhn, G. K. Aluko, and M. Semon, 1997. Interspecific
Oryza sativa L. X O. glaberrima Steud. progenies in upland rice
improvement. Euphytica, 92: 237-246.
Ladizinsky G., 1992. Crossability
relations. In: Kalloo G., J.B.Chowdhury (eds.), Distant hybridization of crop
plants. Springer-Verlag, Berlin. p.15-31.
Morinaga T., and H. Kuriyama,
1957. Cytogenetical studies on Oryza sativa L.. IX. The F1 hybrid of O.
sativa L. and O. glaberrima Steud. Jap. J. Breeding, 7: 57-65
(English with Japanese summary)
Morishima H., K. Hinata, and H. I. Oka,
1962. Comparison between two cultivated rice species, Oryza sativa L. and
O. glaberrima Steud. Jap. J. Breeding, 12: 153-165 (English with
Morishima H., K. Hinata, and H. I. Oka, 1963. Comparison
of modes of evolution of cultivated forms from two wild rice species, Oryza
breviligulata and O. perennis. Evolution, 17: 170-181.
Sano Y., Y. E. Chu, and H. I. Oka, 1979. Genetic studies of speciation in cultivated
rice, 1. Genic analysis for the F1 sterility between O. sativa L. and O.
glaberrima Steud. Jap. J. genetics, 54: 121-132.
Sano Y, 1983.
A new gene controlling sterility in F1 hybrids of two cultivated rice species.
The Journal of Heredity, 74: 435-439.
Tao D., F. Hu, G. Yang,
J. Yang, H. Tao, 1997. Exploitation and utilization of interspecific hybrid vigor
between Oryza sativa and O. glaberrima. In: Jones M. P., M. Dingkuhn,
D. E. Johnson, S. O. Fagade (eds.), Interspecific Hybridization: Progress and
Prospects. Proceedings of the Workshop: Africa/Asia Joint Research on Interspecific
Hybridization between the African and Asian Rice Species (O. glaberrima
and O. sativa ), WARDA, M'be, Bouake Cote d'Ivoire, December 16-18, 1996.
Tao D., F. Hu, Y. Yang, Y. Zhou, H. Chen, 1999. Studies on
the interspecific crossability between Oryza sativa L. and O. glaberrima
Steud. In: Prospects of rice genetics and breeding for the 21st Century:
paper collection of International Rice Genetics and Breeding Symposium. China
Agricultural Scientech Press, Beijing. p. 329-334.