39. Mapping a new gene for resistance to bacterial blight based on RFLP markers

    Xing-Hua Lin, Duan-Pin Zhang, Yue-Feng Xie, Qi-Fa Zhano and He-Ping Gao
    Department of Agronomy, Huazhong Agric. University, Wuhan, 430070 China
 

     Bacterial blight of rice, caused by Xanthomonas oryzae pv. oryzae, is a serious disease prevalent throughout Asia. Some resistant cultivars were identified from 6184 Yunnan local varieties by using 10 bacterial blight strains from China, Philippines and Japan. Zha-Chang-Long (ZCL) a japonica variety was resistant to all bacterial blight stranis used (Chen et al. 1990). The resistance of ZCL to bacterial blight strain "Pxo61" is controlled by a dominant gene. This gene is non-allelic to Xa-I, Xa-2, Xa-3 and Xa-14 (Xie et al. 1990). We mapped this gene based on RFLP markers by using bulked segregant analysis (Michelmore et al. 1991; Zhang et al. 1994).
    The mapping population was an F2 of a cross between resistant ZCL and susceptible Zhen-Zhu-Ai, an indica variety. Resistant bulk was made by mixing equal DNA of 30 highly resistant plants of F2 population (lesion length was shorter than 3cm). Susceptible bulk was made by mixing equal DNA of 42 highly susceptible plants (lesion length was longer than 9cm). The DNA samples of 2 parents and 2 bulks were digested with 6 enzymes (BamHI, DraI, EcoRl, EcoRV, HindIIl and XbaI) and were assayed for restriction fragment length polymorphism (RFLP) with 99 cloned fragments kindly provided by Dr. S. D. Tanksley and Dr. T. Sasaki.
    Thirtyfive out of 99 probes were polymorphic between all the parents tested, comprising 35.4%. These polymorphic probes covered about 855cM of rice genome, which is about 58% of Cornell RFLP linkage map (Causse et al. 1994). The ability to verify polymorphism by using genomic clones was higher than that by using cDNA clones, with 44.1% vs. 15.6%, respectively. Twenty eight polymorphic probes showed bands of similar intensity as the parents and the resistant bulk and susceptible bulk. Seven polymorphic probes showed bands similar to those of susceptible parent and the susceptible bulk. It was found that the resistance gene of ZCL is linked to 7 probes, located on chromosome 11. The distances between the resistance gene and probes are shown in Table I. The resistance gene is thus located on chromosome 11 (Fig. 1). The locus of this resistance gene is different from loci of other resistance genes mapped on this chromosome. It therefore appears this is a new dominant gene for resistance to bacterial blight.
 
Table 1. Linkage between RFLP markers and the regi stance gene
Probe Type of band1) p(%)2) Genetic map
distance (cM)
1 2 3 Total
R543 1 2 39 42 4.8±2.3 4.8±2.3
G181 1 5 36 42 8.3±3.0 8.4±3.0
RZ536 1 7 34 42 10.7 ±3.4 10.9±3.4
C950 1 7 34 42 10.7+3.4 10.9 ±3.4
G389 2 8 32 42 14.3 ±3.8 14.7±3.8
RG1109 3 17 22 42 27.4±4.9 30.8±4.9
G4001 3 17 22 42 27.41:4.9 30.8±4.9

1 ) 1. No. of plants with resistant parent band.
     2. No. of plants with two parent bands.
     3. No. of plants with susceptible parent band.
2) Recombination frequencies between markers and the gene for
resistance to bacterial blight.
 

Fig. 1. The locus of gene for resistance to bacterial blight on chromosome 11 in Yunnan rice variety Zha-Chang-Long based on RFLP linkage.

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