Phytopathology. 2004 Dec;94(12):1376-82. doi: 10.1094/PHYTO.2004.94.12.1376.
ABSTRACT The lack of durability of host plant disease resistance is a major problem in disease control. Genotype-specific resistance that involves major resistance (R) genes is especially prone to failure. The compatible (i.e., disease) host-pathogen interaction with systemic acquired resistance (SAR) has been studied extensively, but the incompatible (i.e., resistant) interaction less so. Using the pepper-bacterial spot (causal agent, Xanthomonas axonopodis pv. vesicatoria) pathosystem, we examined the effect of SAR in reducing the occurrence of race-change mutants that defeat R genes in laboratory, greenhouse, and field experiments. Pepper plants carrying one or more R genes were sprayed with the plant defense activator acibenzolar-S-methyl (ASM) and challenged with incompatible strains of the pathogen. In the greenhouse, disease lesions first were observed 3 weeks after inoculation. ASM-treated plants carrying a major R gene had significantly fewer lesions caused by both the incompatible (i.e., hypersensitive) and compatible (i.e., disease) responses than occurred on nonsprayed plants. Bacteria isolated from the disease lesions were confirmed to be race-change mutants. In field experiments, there was a delay in the detection of race-change mutants and a reduction in disease severity. Decreased disease severity was associated with a reduction in the number of race-change mutants and the suppression of disease caused by the race-change mutants. This suggests a possible mechanism related to a decrease in the pathogen population size, which subsequently reduces the number of race-change mutants for the selection pressure of R genes. Thus, inducers of SAR are potentially useful for increasing the durability of genotype-specific resistance conferred by major R genes.
摘要 寄主植物抗病性的耐久性缺乏是疾病控制的一个主要问题。涉及主要抗性（R）基因的基因型特异性抗性特别容易失效。已广泛研究了与系统获得性抗性（SAR）相容（即发病）的寄主-病原体相互作用，但对不相容（即抗性）的相互作用研究较少。利用辣椒细菌性斑点病（病原菌为黄单胞菌属番茄斑点病致病变种）病系，我们研究了 SAR 对减少在实验室、温室和田间试验中克服 R 基因的致病变种出现的影响。携带一个或多个 R 基因的辣椒植株用植物防御激活剂 acibenzolar-S-methyl（ASM）喷洒，并与病原体的不相容菌株进行了挑战。在温室中，接种后 3 周首次观察到病害斑。携带主要 R 基因的经 ASM 处理的植株上，由不相容（即过敏）和相容（即发病）反应引起的病斑数量明显少于未经喷洒的植株。从病斑中分离出的细菌被确认为致病变种突变体。在田间试验中，检测到致病变种的时间延迟，且病情严重程度降低。病情严重程度的降低与致病变种数量的减少以及致病变种引起的病害的抑制有关。这表明存在与病原体种群大小减少相关的可能机制，从而减少了 R 基因选择压力下的致病变种数量。因此，SAR 的诱导物可能有助于提高主要 R 基因赋予的基因型特异性抗性的耐久性。
