7. Genetic differentiation of wild-rice population in China

Yan-Hong Huang and Xiang-Kun Wang

Agronomy Dept., Beijing Agric. University, Beijing, 100094 China

Whether or not the common wild rice of China is differentiated into the Indica and Japonica types is a disputable question. Previous workers, e.g., Oka and Morishima 1982, Second 1985, Morishima and Gadrinab 1987, and Sano et al. 1989, who investigated Chinese wild rice from different aspects presented their viewpoints.

In the present study, materials were collected from three natural populations growing at Dongxing in Jiangxi, and Guilin and Fusui in Guangxi. The former two are isolated from cultivated rice. but the last one is near rice fields. The plants sampled were analyzed for isozymes at seven loci, i.e., Est-3, Cat-1, Amp-2, Acp-1, Acp-2, Mal-1, and Mal-2, by using polyacrylamide gel electrophoresis. A self-pollinated progeny line showing a fixed isozyme pattern was taken from each plant as a strain.

        Average gene diversity was computed as: H=1/n ∑ of j (1-∑ of i ,x_ij²), where x_ij is the

frequency of gene i at locus j and n is the number of loci examined. The values obtained for the three sites are given in Table 1. Fusui population had the highest gene diversity and Dongxiang population the lowest. Possibly, the high diversity of Fusui population is attributable to introgression of genes from cultivated rice.

The Indica (or Hsien, H) and Japonica (or Keng, K) types have different alleles at each of the seven isozyme loci, and accordingly show different allelic constitutions as shown in Table 2. Many plants examined had a combination of the alleles from typical Indica and Japonica parents. Those having more than four (4, 5 and 6) Japonica-type alleles were taken as Japonica-cline (K') and more than four Indica-type alleles as Indica-cline (H'). Then. the wild-rice strains examined, 92 in total, were classified into 5K. 74K' and 13H' types: there was no true H types (Table 2).

The frequencies of K, K' and H' types among strains from the three sites are given in Table 3. The plants from Dongxiang were mostly of K' type, although K' was generally dominant at all sites. In the light of this observation, the Chinese common wild rice may be considered to have a potentiality of Indica-Japonica differentiation, even though the plants are not differentiated yet.

Table 1. Average gene diversity (H) estimated in three populations of wild rice

Table 3. Number of strains classified as K, K' and H' types in three populations

K:    having Japonica alleles at all 7 loci
K': having Japonica alleles at 4,5 or 6 loci
H':    having Indica alleles at 4,5 or 6 loci

References

Cai, H. W. and X. K. Wang. 1993. Is the common wild rice differentiated inn) Keng types in China? RGN 10: 68-70.

Morishima, H. and L. U. Gadrinab. 1987. Are the Asian common wild rice differentiated into the Indica and Japonica types. In S. C. Hsieh (ed.). Crop Exploration and Utilization of Genetic Resources, p. 11-20. Taichung Distr. Agric. Improvement Station. Changhua. Taiwan. ROC.

Oka, H. I. and H. Morishima. 1982. Phylogenelic differentiation of cultivated rice. 23. Potentiality of wild progenitors to evolve the Indica and Japonica types of rice cultivars. Euphytica 31: 41-50.

Sano, Y., H. Z. Yi, Q. Q. Shao and S. Iyama, 1989. Ribosomal DNA spacer-length variations in a wild-rice population from Dongxiang. China. Proc. 6th Intern. Congr. of SABRAO. p.493-496.

Second, G., 1985, Evolutionary relationships in the sativa group of Oryza based on isozyme data. Genet. Sel. Evol. 17(1): 89-114.