Xinhua LIN1, Gongxin Yu1, Duanpin ZHANG1, Yuefeng XIE1, and Yong CHEN2
1) Dept. of Agronomy, Huazhon Agric. University, Wuchang, 430070 China
2) Crop Genetic Resources Station, Yunnan Acad. Agric. Sciences, Kunming, 650205 China
The resistance of a Yunnan variety Dong-Nuo (Oryza sativa) to bacterial blight strain (Xanthomonas campestris pv. oryzae) Jiangling 691 from Hubei expressed at all stages of plant growth was found to be governed by a recessive gene tentatively designated as xa-k. In order to determine its chromosomal location, we crossed Dong-Nuo with the series of primary trisomics which were resistant to the bacterial blight strain Jiangling 691, controlled by a dominant gene Xa-a (Zhao et al. 1985). The trisomic series were made available through the kindness of Dr. G. S. Khush.
The parents, F1 plants and F2 populations were inoculated by Jiangling 691 at the booting stage. The F1 plants, trisomic as well as disomic, of all the crosses were resistant. The F2 populations from 10 crosses segregated in a 13R: 3S [(3R: 1S) (1R: 3S)] ratio except for two crosses, triplo 7 X Dongnuo and triplo 11 X Dongnuo. If xa-k is located on chromosome 7 (extra), the trisomic F1 plants from triplo 7 X Dongnuo would have Xa-a+ and xa-k++. To examine this hypothesis, we tested 595 F2 plants, of which 125 were trisomic and 470 were disomic. In the trisomic fraction, 91 were resistant and 34 were susceptible. This fitted a 3: 1 ratio (X2 = 0.23) which is expected as (3R: 1S)(0R: 4S). In the disomic fraction of this cross, 351 were resistant and 119 were susceptible which agreed with a 7R : 2S ratio (X2 = 2.43) expected as (3R : 1S) (1R : 8S). These results indicated that xa-k was located on chromosome 7.
If Xa-a is located on chromosome 11, the trisomic F1 plants from triplo 11 x Dongnuo would have Xa-a Xa-a+ and xa-k+. Among the F2 trisomic plants, 220 were resistant and 16 were susceptible. This agreed with a 17R: 1S ratio (X2 = 0.14), indicating that Xa-a was located on chromosome 11 as reported by Yu et al. (1986).
Yu, G. X., D. P. Zhang and X. F. Xie, 1986. Location of genes for resistance to Chinese strains of bacterial blight, Xanthomonas campestris pv. oryzae in IR28. RGN 3: 86-87.
Zhao, X. P., D. P. Zhang and Y. F. Xie, 1985. Studies on the inheritance of rice to bacterial blight. J. Huazhong Agric. Coll. 3: 11-12. (in Chinese with English summary)