Department of Biology, School of Science, University of Waikato, Hamilton, New Zealand.
Department of Environmental Science, Policy & Management, University of California, Berkeley, CA, United States of America.
PLoS One. 2018 Dec 10;13(12):e0208961. doi: 10.1371/journal.pone.0208961. eCollection 2018.
Chemical treatments are used widely in agricultural and natural settings to protect plants from diseases; however, they may exert an important selection pressure on plant pathogens, promoting the development of tolerant isolates through adaptive evolution. Phosphite is used to manage diseases caused by Phytophthora species which include a large number of the most economically damaging plant pathogens worldwide. Phosphite controls the growth of Phytophthora species in planta without killing it; as a result, isolates can develop tolerance to phosphite after prolonged exposure. We investigated the inter- and intra-specific variability in phosphite tolerance of eleven Phytophthora species, including P. ramorum, an internationally important, highly regulated pathogen. Phytophthora ramorum is a good model system because it is comprised of multiple genetically homogeneous lineages. Seven species were found to be consistently sensitive to phosphite based on the low Effective Concentration (EC) 50 values of all isolates tested (amount of phosphite required to inhibit mycelial growth by 50% relative to growth in the absence of phosphite). However, P. ramorum, P. lateralis, P. crassamura and P. cambivora showed intraspecific variability in sensitivity to phosphite, with at least one isolate showing significantly higher tolerance than the other isolates. Within the three P. ramorum evolutionarily divergent lineages tested, NA1 was the most susceptible to phosphite, the NA1 and EU1 lineages showed intralineage variability and the NA2 lineage showed a decreased sensitivity to phosphite overall as all isolates were relatively tolerant. This finding is relevant because NA1 is dominant in the wild and can be controlled using phosphite, while the EU1 lineage has recently been identified in the wild and is phosphite-tolerant, making the treatment approach potentially less effective. Phytophthora ramorum, P. lateralis and P. crassamura are either selfing, homothallic species, or are known to reproduce exclusively clonally, indicating tolerance to phosphite can emerge even in the absence of sexual recombination.
化学处理广泛用于农业和自然环境中，以保护植物免受疾病侵害；然而，它们可能对植物病原体施加重要的选择压力，通过适应性进化促进耐受分离株的发展。亚磷酸盐被用于管理由疫霉属物种引起的疾病，这些物种包括全球大多数经济破坏性最强的植物病原体。亚磷酸盐控制疫霉属物种在植物体内的生长而不将其杀死；因此，在长时间暴露后，分离株可以对亚磷酸盐产生耐受性。我们调查了 11 种疫霉属物种（包括 P. ramorum）的亚磷酸盐耐受力的种间和种内变异性，P. ramorum 是一种具有国际重要性的、高度受监管的病原体。P. ramorum 是一个很好的模型系统，因为它由多个遗传上同质的谱系组成。根据所有测试分离株的低有效浓度（EC）50 值，七种物种被发现对亚磷酸盐始终敏感（相对于不存在亚磷酸盐的情况下抑制菌丝生长 50%所需的亚磷酸盐量）。然而，P. ramorum、P. lateralis、P. crassamura 和 P. cambivora 显示出对亚磷酸盐敏感性的种内变异性，至少有一种分离株比其他分离株表现出明显更高的耐受性。在所测试的三个 P. ramorum 进化上有差异的谱系中，NA1 对亚磷酸盐最敏感，NA1 和 EU1 谱系显示出谱系内变异性，而 NA2 谱系总体上对亚磷酸盐的敏感性降低，因为所有分离株都相对耐受。这一发现是相关的，因为 NA1 在野外占主导地位，可以用亚磷酸盐控制，而 EU1 谱系最近在野外被发现，并且对亚磷酸盐具有耐受性，使得治疗方法可能效果降低。P. ramorum、P. lateralis 和 P. crassamura 要么是自交的、同型交配的物种，要么是已知仅通过无性繁殖繁殖的物种，这表明即使没有有性重组，对亚磷酸盐的耐受性也可能出现。
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