Metapopulation Research Group, Department of Biosciences, University of Helsinki, Helsinki, Finland.
J Evol Biol. 2013 Aug;26(8):1716-26. doi: 10.1111/jeb.12169. Epub 2013 May 23.
The sexual stage of pathogens governs recombination patterns and often also provides means of surviving the off-season. Despite its importance for evolutionary potential and between-season epidemiology, sexual systems have not been carefully investigated for many important pathogens, and what generates variation in successful sexual reproduction of pathogens remains unexplored. We surveyed the sexually produced resting structures (chasmothecia) across 86 natural populations of fungal pathogen Podosphaera plantaginis (Ascomycota) naturally infecting Plantago lanceolata in the Åland archipelago, southwestern Finland. For this pathosystem, these resting structures are a key life-history stage, as more than half of the local pathogen populations go extinct every winter. We uncovered substantial variation in the level of chasmothecia produced among populations, ranging from complete absence to presence on all infected leaves. We found that chasmothecia developed within clonal isolates (single-strain cultures). Additionally, these clonal isolates all contained both MAT1-1-1 and MAT1-2-1 genes that characterize mating types in Ascomycetes. Hence, contrary to expectations, we conclude that this species is capable of haploid selfing. In controlled inoculations, we discovered that pathogen genotypes varied in their tendency to produce chasmothecia. Production of chasmothecia was also affected by ambient temperature (E) and by the interaction between temperature and pathogen genotype (G × E). These G, E and G × E effects found both at a European scale and within the Åland archipelago may partly explain the high variability observed among populations in chasmothecia levels. Consequently, they may be key drivers of the evolutionary potential and epidemiology of this highly dynamic pathosystem.
病原体的有性阶段控制着重组模式，通常也为其在淡季的存活提供了手段。尽管有性生殖对于进化潜力和季节间流行病学都很重要，但许多重要病原体的有性生殖系统并没有被仔细研究过，病原体有性生殖成功的变异来源仍未被探索。我们调查了真菌病原体 Podosphaera plantaginis（子囊菌门）在其自然感染芬兰西南部 Åland 群岛的 Plantago lanceolata 时，在 86 个自然种群中产生的有性生殖休眠结构（闭囊壳）。对于这个病原系统，这些休眠结构是一个关键的生活史阶段，因为超过一半的当地病原体种群每年冬天都会灭绝。我们发现，不同种群之间产生的闭囊壳数量存在很大差异，从完全不存在到所有受感染的叶片上都存在。我们发现闭囊壳是在克隆分离株（单株培养物）中发育的。此外，这些克隆分离株都含有 MAT1-1-1 和 MAT1-2-1 基因，这些基因特征描述了子囊菌中的交配类型。因此，与预期相反，我们得出的结论是，这个物种能够进行单倍体自交。在受控接种实验中，我们发现病原体基因型在产生闭囊壳的倾向方面存在差异。闭囊壳的产生也受到环境温度（E）和温度与病原体基因型（G×E）相互作用的影响。在欧洲范围内和 Åland 群岛内都发现了这些 G、E 和 G×E 效应，它们可能部分解释了我们在闭囊壳水平上观察到的种群间高度变异。因此，它们可能是这个高度动态病原系统进化潜力和流行病学的关键驱动因素。
