4. Classification of weed-rice strains based on isozyme variation

1) Department of Agronomy, College of Agriculture and Animal Science, Yeungnam University, Kyeongsan, Korea

2) National Institute of Genetics, Mishima, 411 Japan

To examine isozyme variation, 139 strains of weed rice collected from all over South Korea (foregoing report by Suh; Suh et al. 1992) were examined for allelic variation at 14 isozyme loci, i.e., Acp-1, Amp-1, Amp-2, Amp-3, Cat-1, Est-2, Est-5, Pgd-1, Pgd-2, Pgi-1, Pgi-2, Pgi-3, Pox-2 and Sdh-1. For comparison, 51 weedy strains collected in countries other than Korea were also examined, i.e., 9 from Bangladesh, 16 from Bhutan, 2 from Brazil, 4 from China, 3 from India, 3 from Japan (so-called red rice), 10 from Nepal, 2 from Thailand, and 2 from USA. All the isozyme loci were polymorphic among the strains tested. Correlations were computed between the 14 loci based on allelic identity, and were subjected to principal component analysis. The 190 weedy strains and 4 cultivars were scattered according to the scores given by the first and second component vectors (Fig. 1).

The weed-rice strains were divided into two distinct groups as shown in Fig. 1, by the first component vector which stood for 48% of total variation. One group containing Taichung 65 (T65) and Nakdongbyeo and scattered on the right side of the figure seems to represent the Japonica type; the other group containing IR36 and Peh-kuh and scattered on the left side represents the Indica type. Among Korean weedy strains, this pattern corresponds exactly to the long-grain and short-grain types. The strains from China and Bhutan contained both the Indica and Japonica types. Those from Bangladesh, Brazil, India, Japan, Nepal, Thailand and USA were all Indica types.

As shown in Fig. 1, variations within the Japonica group were narrow and simple, but the Indica types were much more variable. In the Indica group, many of strains from tropical countries were scattered in the lower part of the

figure, and those from temperate countries in the upper part, by the second vector. Among the isozyme loci, Acp-1, Cat-1, Pgi-3, Amp-2 and Est-2 had large loadings on the first vector, and Amp-3, Sdh-1 and Pgd-1 had large loadings on the second vector. It seems that the former five isozyme loci contribute to the division of weedy strains into Indica and Japonica types, and the latter three loci contribute to differentiation of the Indica weed rices into tropical and temperate forms. The present study shows that the differentiation pattern of weed-rice strains at the isozyme level is quite similar to that of Asian rice cultivars as reported by Glaszmann (1987) and by Tang et ai. (1989). This suggests gene flow between weed rices and cultivars.

References

Glaszmann, J. C., 1987. Isozymes and classification of Asian rice varieties. Theor. Appl. Genet. 74: 21-30.

Tang, L. H., Y. I. Sato and H. Morishima, 1989. Differences in isozymes between indica and japonica rice cultivars. Chinese J. Rice Sci. 3: 141-144. (in Chinese)