Data from: Recent range expansion and agricultural landscape heterogeneity have only minimal effect on the spatial genetic structure of the plant pathogenic fungus Mycosphaerella fijiensis

Understanding how geographical and environmental features affect genetic variation at both the population and individual levels is crucial in biology, especially in the case of pathogens. However, distinguishing between these factors and the effects of historical range expansion on spatial genetic structure remains challenging. In the present study, we investigated the case of Mycosphaerella fijiensis-a plant pathogenic fungus that has recently colonized an agricultural landscape characterized by the presence of potential barriers to gene flow, including several commercial plantations in which disease control practises such as the use of fungicides are applied frequently, and low host density areas. We first genotyped 300 isolates sampled at a global scale on untreated plants in 2 dimensions over a 50x80 Km area. Using two different clustering algorithms, no genetic structure was detected in the studied area, suggesting expansion of large populations and/or no influ ence of potential barriers. Second, we investigated the potential effect of disease control practises on M. fijiensis diversity by comparing populations sampled in commercial vs. food-crop plantations. At this local scale, we detected significantly higher allelic richness inside commercial plantations compared to the surrounding food-crop plantation populations. Analysis of molecular variance (AMOVA) indicated that 99% of the total genetic variance occurred within populations. We discuss the suggestion that high population size and/or high migration rate between populations might be responsible for the absence of any effect of disease control practises on genetic diversity and differentiation.

阐明地理与环境特征如何在种群及个体层面影响遗传变异，是生物学领域的核心议题之一，对于病原物研究而言尤为关键。然而，区分上述因素与历史范围扩张对空间遗传结构的影响，仍是一项颇具难度的研究挑战。本研究以斐济球腔菌（Mycosphaerella fijiensis）为研究对象——该真菌为一种新近入侵农业生境的植物病原真菌，其所在的农业景观存在潜在的基因流（gene flow）障碍，包括频繁施用杀菌剂等病害防控措施的商业化种植园，以及寄主密度较低的区域。首先，我们对50×80公里二维研究区域内采自未施药植株的300个真菌分离株进行基因分型，采样采用全球尺度的布点策略。通过两种不同的聚类算法分析，研究区域内未检测到显著的遗传结构，这提示该种群可能存在大规模扩张，或是潜在的基因流障碍未对其产生影响。其次，我们通过对比商业化种植园与粮食作物种植园的采样种群，探究病害防控措施对斐济球腔菌多样性的潜在影响。在该局域尺度下，我们发现商业化种植园内的种群等位基因丰富度（allelic richness）显著高于周边粮食作物种植园的种群。分子变异分析（Analysis of Molecular Variance, AMOVA）结果显示，总遗传变异的99%均存在于种群内部。我们针对“种群规模庞大和/或种群间迁移率较高，可能是病害防控措施未对遗传多样性与分化产生影响的原因”这一假说展开讨论。