Fig. 1. A dendrogram of 25 Indica rice varieties.
Biotechonology Department, China National Rice Research Institute (CNRRI), Hangzhou, 310006 China
Extensive cultivation of improved semidwarf varieties has increased rice production dramatically. However, a majority of rice varieties grown in China are genealogically (in pedigree) related to a small number of primary parents. For example, most of early and middle season indica varieties can be traced back to Nan-te-hao (including its derivatives, Ai-jiao-nan-te, Lu-cai-hao and Lian-tang-zao), Ai-zi-zhan, Di-jiao-wu-jian, and Sheng-li-xian. The semidwarfism of almost all indica varieties is controlled by gene sd-1 (Lin and Min 1991). The narrowed genetic basis may lead to genetic vulnerability, although the extent of relatedness of the varieties remains unknown.
Table 1. A list of tested rice varieties _______________________________________________________________________________ No. Variety Combination Yeara Origin _______________________________________________________________________________ 1 Nan-te-hao From Po-yang-zao 1934 Jiangxi 2 Lu-cai-hao From Nan-te-hao 1948 Fujian 3 Lian-tang-zao Gan-nong 3425/Nan-te-hao 1954 Iiangxi 4 Ai-jiao-nan-te From Nan-te-hao 1956 Guangdong 5 Ai-zi-zhan Landrace - Guangxi 6 Di-jiao-wu-jian Landrace - Taiwan 7 Xian-feng I Guang-chang-ai 6/Lu-cai-hao 1969 Zhejiang 8 Guang-lu-ai 4 Guang-chang-ai 3784/Lu-cai-hao 1967 Guangdong 9 Nanjing 11 Nanjing 6/Et-jiu-ai 4 1967 Jiangsu 10 Zhen-long 13 Zhen-shan 96/Long-fei 313 1970 Zhejiang 11 Gui-chao 2 Gui-yang-ai 49/Chao-yang-zao 18 1976 Guangdong 12 Shuang-gui 1 Gui-yang-ai C17/Gui-chao 2 1979 Guangdong 13 Zhe-fu 802 Radiation mutant of Si-mei 2 1980 Zhejiang 14 Zhu-ke 2 Zhu-lian-ai/Ke-ai 13 1975 Zhcjiang 15 Zhong 83-49 Si-fcng 43/Zhu-ke 2 1982 Zhejiang 16 Lu-hong-zao I 1277/Hong 410 1983 Sichuan 17 Te-qitig Te-ai/Ye-qing-lun 1984 Guangdong 18 Min-ke-zao I From 78130 1985 Fujian 19 Zhong 156 Zhe-fu 802/Xiang-zao-xian 2 1986 Zhejiang 20 Zhong 86-44 Zhe-fu 802/Guang-lu-ai 4//HA79317-7 1984 Zhejiang 21 Ai-mei-zao 3 (Ai-qing 569/Hong-mei-xuan)F`4`/Gui-chao 2 1979 Guangdong 22 Gu-mei 2 Fujian 23 IR30 Phillipines 24 Tetep Vietnam 25 Hong-jiao-zhan Guangxi _______________________________________________________________________________ a. The year when the variety was developed.In the present study, RFLPs were analyzed for 25 early and mid-season indica varieties using 50 DNA probes. As listed in Table 1, the varieties tested include six primary parents (1-6), 15 commercial varieties (7-21) and four donor parents for blast resistance (22-25). The seeds of these varieties were provided by Genetics and Breeding Department and Germplasm Department, CNRRI, Hangzhou. DNA clones were obtained from Dr. Tanksley's laboratory, Cornell University, Ithaca, New York.
Fig. 1. A dendrogram of 25 Indica rice varieties.
After treatment with endonuclease EcoRI, 26 probes distributed over all 12 chromosomes showed polymorphism among the varieties tested. All the varieties could be distinguished from one another. A total of 73 polymorphic fragments were detected among 101 hybridization fragments.
The proportion of DNA fragments shared between varieties was calculated and a dendrogram showing mutual similarity of the 25 varieties was constructed by using Nei's formula (1987). The result is presented in Fig. 1. The rice varieties tested were clustered into two groups excluding IR30 and Ai-mei-zhao 3.
The six primary parents showed a high degree of similarity with each other (Table 2) and with most of commercial varieties, suggesting that the genetic uniformity of improved varieties is largely due to the narrow background of their primary parents.
Table 2. Proportions of shared DNA fragments between 6 primary parents of
early and middle season indica rice varieties (%)
_______________________________________________________________________________
Variety No* 1 2 3 4 5
_______________________________________________________________________________
2 93.7
3 82.3 87.1
4 94.4 99.2 87.8
5 84.8 88.0 81.3 87.1
6 94.6 96.1 83.5 95.3 89.1
_______________________________________________________________________________
See Table 1 for varietal names.
On the other hand, all the donor parents for blast resistance as well as the
blast resistant varieties Ai-mei-zhao 3 and Min-ke-zao 1 appeared to be more
diversified than other varieties. This suggests that genetic uniformity may
affect the extent and durability of blast resistance.References
Lin, S. C. and S. K. Min, 1991. Rice varieties in China and their genealogy. Shanghai Science and Technology Press, Shanghai. (in Chinese)
Nei, M., 1987. Molecular Evolutionary Genetics. Columbia Univ. Press, New York.