5. Is the common wild rice differentiated into Keng types in China?

Hong-Wei CAI and Xiang-Kun WANG

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

Oka and Morishima (1982) reported that O. rufipogon, thought to be the wild progenitor of O. sativa, is not differentiated into the Hsien (Indica) and Keng (Japonica) types, although it shows a latent tendency for such differentiation. Recently, Morishima and Gardinab (1987) as well as Sano et al. (1989) are inclined to consider that the Hsien-Keng differentiation exists in the common wild rice. Second (1985) proposed more distinctly that the common wild rice is differentiated into Hsien and Keng types and the plants in China are largely of the Keng type. However, these workers do not mention whether their wild-rice materials are homozygous or heterozygous produced as a result of introgressive hybridization with cultivated rice.

In the present study, the wild-rice materials were classified into homozygous and heterozygous types. A total of 92 homozygous strains of Chinese wild rices were then selected and tested for isozymes at four loci, Cat-1, Amp-2, Est-2 and Acp-2. The results given in Table 1 show that the strains tested were classified into 17 groups each representing a particular combination of alleles at the four loci.

Of them, nos. 1 and 2 in Table 1, were taken as typical Hsien (H), and another, no. 17, as typical Keng (K). The atypical ones (no. 2-16) were classified into Hsien-cline (H', differing in one allele from H), Keng-cline (K', differing in one allele from K), and intermediate group (I, differing from H or K at two or more loci). The mode of variation from H to K types appeared to be continuous.

A greater part of the strains belonged to K' (47.8%), I (25.0%) and H' (13.0%) groups, and only a small proportion belonged to typical Hsien (4.3%) and Keng (9.8%) genotypes. Strains belonging to the K and K' groups were larger in number than those belonging to the H and H' groups.

Their geographical distribution is shown in Table 2. The strains from Dong-xiang (Jiangxi) and Chaling (Hunan) were mostly of K' type. Among the strains from Guangdong and Guangxi, K' types were also predominant. The materials from Yuanjiang, Yunnan belonged to the intermediate group.

Besides, 13 homozygous strains of O. rufipogon from India and Thailand were observed for comparison. They showed similar variations as the Chinese material, but many were Hsien and Hsien-cline types. It may be concluded that the Chinese common wild rice has a tendency to resemble the Keng type at the isozyme level (cf. Wang et al. 1992).

          
Table 1.  Alleles at four isozyme loci among 92 Chinese common wild-rice
strains
===============================================================================
No.  Strain-group         Allele   found   at          No. of
     classified    Cat-1   Amp-2        Est-2  Acp-2  strains
===============================================================================
1    H                 1       2            1      1        3
2    H                 1       2            2      1        1
3    H'                1       2            0      1        6
4    H'                2       2            1      1        1
5    H'                1       2            1      0        2
6    H'                1       2            2      0        1
7    H'                2       2            2      1        2
8    I                 1       2            0      0        9
9    I                 2       2            2      0        3
10   I                 2       2            0      1        4
11   I                 2       1            2      1        1
12   I                 2       2            1      0        5
13   I                 3       2            1      0        1
14   K'                2       2            0      0       40
15   K'                2       1            0      1        2
16   K'                1       1            0      0        2
17   K                 2       1            0      0        9
===============================================================================
H': differing from H at one locus; K': differing from K at one locus; I:
differing from H or K at two or more loci (intermediate).

          
Table 2. Regional distribution of strain-groups classified into H, H', I, K',
and K
===============================================================
Region or site       H  H'   I  K'  K  No. of strains  
===============================================================
Dongxiang, Jiangxi       1   1   3                  5
Chaling,    Hunan            1   6                  7
Jlangyong, Hunan             2   2                  4
Zhangpu,     Fujian      1   1   1                  3
Guangdong Province       4   4  10                 18
Guangxi    Region    3   8  10  22  9              52
Yuanjiang, Yunnan            3                  3*/92
===============================================================
* In addition, 45 strains were examined.  All belonged to the I group.

References

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.

Oka, H. I. and H. Morishima, 1982. Phylogenetic 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, O. Q. Shao and S. Iyama, 1989. Ribosomal DNA spacer-length variations in a wild-rice population from Dongxiang, China. Proc. 6th Internti. Congr. 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.

Wang, X. K., H. W. Cai and K. S. Cheng, 1992. The discovery of an Est locus related to the origin, evolution and classification of Asian rice. Chinese Rice Res. Newslt. 7: 1-2.