Pruvost Olivier, Boyer Karine, Ravigné Virginie, Richard Damien, Vernière Christian
CIRAD UMR PVBMT Saint Pierre, La Réunion France.
ANSES Saint Pierre, La Réunion France.
Evol Appl. 2019 Apr 10;12(8):1523-1538. doi: 10.1111/eva.12788. eCollection 2019 Sep.
Although some plant pathogenic bacteria represent a significant threat to agriculture, the determinants of their ecological success and evolutionary potential are still poorly understood. Refining our understanding of bacterial strain circulation at small spatial scales and the biological significance and evolutionary consequences of co-infections are key questions. The study of bacterial population biology can be challenging, because it requires high-resolution markers that can be genotyped with a high throughput. Here, we overcame this difficulty for pv. , a genetically monomorphic bacterium causing Asiatic citrus canker (ACC). Using a genotyping method that did not require cultivating the bacterium or purifying DNA, we deciphered the pathogen's spatial genetic structure at several microgeographic scales, down to single lesion, in a situation of ACC endemicity. In a grove where copper was recurrently applied for ACC management, copper-susceptible and copper-resistant pv. coexisted and the bacterial population structured as three genetic clusters, suggesting a polyclonal contamination. The range of spatial dependency, estimated for the two largest clusters, was four times greater for the cluster predominantly composed of copper-resistant bacteria. Consistently, the evenness value calculated for this cluster was indicative of increased transmission. Linkage disequilibrium was high even at a tree scale, probably due to a combination of clonality and admixture. Approximately 1% of samples exhibited within-lesion multilocus polymorphism, explained at least in part by polyclonal infections. Canker lesions, which are of major biological significance as an inoculum source, may also represent a preferred niche for horizontal gene transfer. This study points out the potential of genotyping data for estimating the range of spatial dependency of plant bacterial pathogens, an important parameter for guiding disease management strategies.
尽管一些植物病原细菌对农业构成了重大威胁，但人们对它们生态成功和进化潜力的决定因素仍知之甚少。完善我们对细菌菌株在小空间尺度上的传播以及共感染的生物学意义和进化后果的理解是关键问题。细菌群体生物学的研究可能具有挑战性，因为它需要能够高通量进行基因分型的高分辨率标记。在这里，我们克服了针对引起亚洲柑橘溃疡病（ACC）的基因单态性细菌—— 柑橘溃疡病菌的这一困难。我们使用一种无需培养细菌或纯化DNA的基因分型方法，在ACC流行的情况下，在几个微观地理尺度上，直至单个病斑，解析了该病原体的空间遗传结构。在一个经常使用铜来管理ACC的果园中，对铜敏感和耐铜的柑橘溃疡病菌共存，细菌群体构成三个遗传簇，表明存在多克隆污染。对两个最大的簇估计的空间依赖性范围，主要由耐铜细菌组成的簇的范围是另一个簇的四倍。一致地，为该簇计算的均匀度值表明传播增加。即使在树木尺度上，连锁不平衡也很高，这可能是由于克隆性和混合的综合作用。大约1%的样本在病斑内表现出多位点多态性，这至少部分是由多克隆感染造成的。溃疡病斑作为接种源具有重要的生物学意义，也可能是水平基因转移的首选生态位。这项研究指出了基因分型数据在估计植物细菌病原体空间依赖性范围方面的潜力，这是指导疾病管理策略的一个重要参数。
