水稻白叶枯病菌致病型的代表意义及菌株毒性变异的内在原因探讨

THE MEANING OF A PATHOTYPE OF LEAF BLIGHT OF RICE CAUSED BY Xanthomonas oryzae PV.Oryzae AND THE INTERNAL AGENTS OF THE STRAINS' VIRULENT VARIATION

对冰箱斜面保存的０、Ⅱ、Ⅳ致病型模式株与其后代单菌落子株致病力的比较，并测定０、Ⅱ、Ⅳ型模式株两两混配液的致病力和观察２２个菌株在中茬和晚茬的致病型鉴别品种上致病力的变异情况，结果表明：采取病叶段沙培，在切口取菌胶的方式分离所得菌株是含不同毒力细胞的混合体，其毒力差异是由各细胞间的组成比和互作关系决定的；用这样的菌株划分出的致病型，实际是病菌不同毒力细胞在一定生态条件下的组成比和互作关系的表型反应，即病菌自然群体毒力结构的反应；鉴于致病型代表菌株是不同毒性细胞的混合体，不同的生态条件，必然会导致其组成比的变异，所以菌株毒力的变异是绝对的，不变是相对的。

The virulence of the model strains of the pathotype O,Ⅱ and Ⅳ of X. oryzae pv. oryzae which had been reserved on the slants of a refrigerator for 2 years was compared with that of their doughter strains which were developed from the single colonies isolated from the model strains. Meanwhile,the virulences of the mixtures between the model strains of pathotype O,Ⅱ and Ⅳ in the proportions of 1 to 1, 1 to 3 and 3 to 1 were determined, and the virulent variation of 22 strains on the pathotype differential hosts cultivated from intermediate and second rice was abserved. From the above experiments, the following conclusions may be obteined:The strains of X. oryzae pv. oryzae(which were isolated by picking up barterial oozes from the top cutting lines of infected leaves plunged in the sand with water)are the mixtures with different virulent cells. The virulent differences among the strains are decided by the interaction and the component proportion of different virulent cells. Therefore,the pathotypes classified by such strains are actually the phenotypic reactions of the interactions and component proportions of different virulent cells in certain ecological environment, i. e. the reaction of the natural virulent structures of the field populations of X. oryzae pv. oryzae. As the strains of the pathotypes were the mixtures described above, their component proportions were inevitably affected by various ecological conditions. So the virulent variation of the strains is absolute and their stability was relative.