水稻白叶枯菌自然群体的毒力结构与致病力的关系

Relationship Between Virulence Structure and Pathogenicity of Field Population of Xanthomonas campestris pv. oryzae

从水稻白叶枯病叶标样151份中,分离获得80个原始菌株,又从原始菌株稀释分离得单菌落菌株441个。对感病品种金刚30、金南风和抗病品种早生爱国3号、矢租,徐444分别剪叶接菌。并对接菌后发现的弱毒菌进行血清学测定。结果表明,在自然条件下存在水稻白叶枯菌的弱毒菌型,它们在血清学方面与强毒菌是同质的。因此水稻白叶枯菌自然群体是由包括基本无毒性的弱毒菌在内的不同致病型组成的混合群体,其中弱毒菌对强毒菌毒性的抑制可表现出数量的或质量的差异。弱毒菌对强毒菌毒性的抑制随弱毒菌在混合接种物中所占比例的增加而加强。代表自然群体的原始菌株的致病力与其毒力结构紧密相关。

From major diseased areas of nine provinces(or municipality)in China, 151 rice leaf samples infected by Xanthomonas campestris pv. oryzae, the causal organism of bacterial blight, were collected. Eighty original isolates were isolated from the samples, and 441 single-colony isolates were further isolated from the original isolates by the dilution method. The isolates were inoculated for comparison of their pathogenicity on susceptible cultivars Jingang 30 and Kinmaze and resistant cultivars Wase Aikoku 3 (carrying the gene Xa-3), Shizu and Xu 444 by the clipping method. The avirulent isolates observed by inoculation underwent ser-ological tests for the identification of homogeneity. The results showed that there was a specific differential interaction of the pathogen and host, and the avirulent isolates were serologically homogenous with the virulent isolates. Twelve pairs of avirulent and virulent isolates from the same original isolates were mixed in different proportions and inoculated on the susceptible cultivar Jingang 30 together with the avirulent, virulent and original isolates. It was found that the inhibition effect of avirulent against virulent isolates mixed in different combinations differed quantitatively or qualitatively. The inhibition effect was increased with the increasing proportion of the avirulent isolate in mixed inoculum. It suggested that the field population of X. c. pv. oryzae were mixtures of the avirulent form and different pathotypes. The pathogenicity of the field population of X. c. pv. oryzae was closely related to its virulence structure. Hence, not only pathotypes should be investigated, the relationship between virulence structure and pathogenicity should also be analysed as monitoring the dynamics of the field populations of X. c. pv. oryzae.