Division of Ecology and Evolution, Research School of Biology, ANU College of Science, The Australian National University, RN Robertson Building, 46 Sullivans Creek Road, Canberra, ACT, 2600, Australia.
BMC Evol Biol. 2019 Jul 8;19(1):139. doi: 10.1186/s12862-019-1446-8.
Pathogens evolve in an arms race, frequently evolving virulence that defeats resistance genes in their hosts. Infection of multiple hosts may accelerate this virulence evolution. Theory predicts that host diversity affects pathogen diversity, with more diverse hosts expected to harbour more diverse pathogens that reproduce sexually. We tested this hypothesis by comparing the microsatellite (SSR) genetic diversity of the barley leaf pathogen Pyrenophora teres f. teres (Ptt) from barley (monoculture) and barley grass (outbreeding). We also aim to investigate host specificity and attempt to track virulence on two barley cultivars, Maritime and Keel.
Genetic diversity in barley Ptt populations was higher than in populations from barley grass. Barley Ptt populations also had higher linkage disequilibrium levels, indicating less frequent sexual reproduction, consistent with the Red Queen hypothesis theory that genetically diverse hosts should select for higher levels of sexual reproduction of the pathogen. SSR analyses indicate that host-associated Ptt populations do not share genotypes and have independent evolutionary histories. Pathogenicity studies showed host specificity as host-associated Ptt isolates could not cross-infect hosts. Minimum spanning network analyses indicated two major clusters of barley Ptt. One cluster represents Maritime virulent and isolates from Western Australia (WA). Low PhiPt population differentiation between WA populations and those from Maritime and Keel, indicated a WA origin of the Maritime and Keel virulences. The main minimum spanning network cluster is represented by a panmictic population structure, represented by isolates from all over Australia.
Although barley Ptt populations are more diverse than barley grass Ptt populations, this may be a result of the size and number of founder Ptt populations to Australia, with larger and more barley Ptt populations introduced. More frequent sexual reproduction of Ptt on barley grass support the Red Queen Hypothesis and suggest evolutionary potential of pathogens on diverse hosts are high. Extensive gene flow of Ptt between regions in Australia is suggested to maintain a panmictic population structure, with human-mediated dispersal aiding in virulence evolution of Ptt on barley.
病原体在军备竞赛中进化，经常进化出毒力，从而击败宿主中的抗性基因。感染多个宿主可能会加速这种毒力进化。理论预测，宿主多样性会影响病原体多样性，具有更多样化的宿主的预期将拥有更多样化的通过有性繁殖繁殖的病原体。我们通过比较大麦叶病原体 Pyrenophora teres f. teres（Ptt）在大麦（单一种植）和大麦草（异花授粉）中的微卫星（SSR）遗传多样性来检验这一假设。我们还旨在研究宿主特异性并尝试追踪两种大麦品种 Maritime 和 Keel 上的毒力。
大麦 Ptt 种群的遗传多样性高于大麦草种群。大麦 Ptt 种群的连锁不平衡水平也较高，表明有性繁殖较少，这与红皇后假说理论一致，即遗传多样性较高的宿主应选择病原体进行更高水平的有性繁殖。SSR 分析表明，与宿主相关的 Ptt 种群不共享基因型，并且具有独立的进化历史。致病性研究表明宿主特异性，因为与宿主相关的 Ptt 分离株不能交叉感染宿主。最小生成树网络分析表明大麦 Ptt 有两个主要聚类。一个聚类代表了 Maritime 毒力和来自西澳大利亚州（WA）的分离株。WA 种群与 Maritime 和 Keel 种群之间的 PhiPt 种群分化较低，表明 Maritime 和 Keel 毒力起源于 WA。主要的最小生成树网络聚类代表了一个泛化种群结构，由来自澳大利亚各地的分离株代表。
尽管大麦 Ptt 种群比大麦草 Ptt 种群更具多样性，但这可能是澳大利亚引入的 Ptt 创始种群的大小和数量的结果，引入了更大和更多的大麦 Ptt 种群。大麦草上 Ptt 的有性繁殖更为频繁，支持红皇后假说，并表明病原体在多样化宿主上的进化潜力很高。澳大利亚各地区之间 Ptt 的广泛基因流表明维持了一个泛化的种群结构，人类介导的扩散有助于 Ptt 在大麦上的毒力进化。
