The F\2\ chlorosis caused by a set of duplicate genes hca-1 and hca-2 was
reported by Sato et al. (1984; previously symboled ch-1-b and ch-1-a,
respectively). To examine the distribution of gene hca-1, 108 native rice
cultivars from various Asian countries were test-crossed with strain J-147
crrying hca-2. The F\1\ plants were grown in 1985, and the F\2\ seeds, more
than 200 per cross, were germinated in the spring of 1986. The genotypes of
each test-crossed variety was judged by its F\2\ segregation. If chloritic
segregants occurred, the variety was considered to have hca-1; if not, it was
considered to carry hca-1+.
The hca-1 gene was distributed in 70 of the 108 varieties tested or in 12 of the 44 Indica and 58 of the 64 Japonica varieties. The gene seems to have a higher frequency in Japonica than in Indica.
Different kinds of hybrid breakdown have been reported so far, by Oka (1957), Okuno and Fukui (1983) and Yokoo (1984). Furthermore, similar cases were found between a Burmese upland cultivar and a Japanese cultivar (Sato, unpubl.), and between a Korean improved variety and a Japanese variety (Toriyama, pers. comm.). Allelism tests and further studies on gene distributions are needed to understand how these genic changes re related to varietal differentiation.
References
Oka, H.I., 1957. Phylogenetic differentiation of cultivated rice, XV. Complementary lethal genes in rice. Jpn. J. Genet. 32: 83-87.
Okuno, K. and K. Fukui, 1983. Hybrid breakdown in wide crosses of cultivated rice. Jpn. J. Breed 33 (suppl. 2): 112-113.
Sato, Y.I., S. Matsuura and K. Hayashi, 1984. The genetic basis of hybrid chlorosis found in a cross between two Japanese native cultivars. RGN 1: 106- 107.
Yokoo, M., 1984. Female sterility in an Indica-Japonica cross of rice. Jpn. J. Breed. 34: 219-227.