Agronomy Department, Central China Agriculutural University Wuchang, Hubei, China
The resistance of IR28 to Chinese strains of bacterial blight is governed by
two genes designated as Xa-a and Xa-h (Zhao et al. 1985). In order to determine
the chromosomal location of these genes we crossed IR 28 with marker genes v-1,
ws, lg, pr, prp, g, ni, la, z-2, tri, ch-1, bc-1, dl, gl, fgl and Pa kindly
supplied by Dr. G.S. Khush. The F\1\ and F\2\ populations were inoculated with
Chinese strains of bacterial blight Jangling 691 and OS75 from Hubei and
Beijing respectively. Both Xa-a and Xa-h were found to be linked to la(lazy
growth habit) but these genes segregated independently of other marker genes.
In an F\2\ population of 255 plants from the cross M9 and IR 28, there were 200 normal and 55 lazy plants. When this population was inoculated with Jangling 691, the ratio for +R:+S:laR:laS was 168:38:28:31. Similarly, when the F\2\ population was inoculated with OS75, the ratio was 184:39:37:25. These ratios do not agree with the digenic segregation ratio of 9:3:3:1 expected for independent segregation of two genes. These data show that Xa-a and Xa-h are linked with la and located on chromosome 11.
The recombination values between Xa-a and la and Xa-h and la were calculated to be 27.9% and 33.7% respectively. The recombination value between Xa-a and Xa-h was found to be 17% (Fig. 1). However, the allelic relationships of Xa-a and Xa-h with Xa-1h, and Xa-kgh, identified in IR 28 by Yamada (1984) are not known because different strains of bacterial blight were used in two studies.
Fig. 1. Linkage of the resistance genes Xa-a, Xa-h and marker gene la.
References
Yamada, T., 1984. Multiple alleles at the Xa-1 and Xa-kg loci for resistance to bacterial leaf blight. Rice Genetics Newsletter Vol. 1. 97.
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): 11-22 (in Chinese with English summary).
Editor's note. The gene symbol designation does not conform with the rules. These will be changed after the allele tests are completed.