Data from: Migration patterns and changes in population biology associated with the worldwide spread of the oilseed rape pathogen Leptosphaeria maculans

Pathogen introductions into novel areas can lead to the emergence of new fungal diseases of plants. Understanding the origin, introduction pathways, possible changes in reproductive system and population size of fungal pathogens is essential in devising an integrated strategy for the control of these diseases. We used minisatellite markers to infer the worldwide invasion history of the fungal plant pathogen Leptosphaeria maculans, which causes stem canker (blackleg) of oilseed and vegetable brassicas. Clustering analyses partitioned genotypes into distinct populations corresponding to major geographic regions, along with two differentiated populations in Western Canada. Comparison of invasion scenarios using Approximate Bayesian Computation suggested an origin of the pathogen in the USA, the region where epidemics were first recorded, and independent introductions from there over the last few decades into Eastern Canada (Ontario), Europe and Australia. The population in Western Canada appeared to be founded from a source in Ontario and the population in Chile resulted from an admixture between multiple sources. A bottleneck was inferred for the introduction into Western Canada but not into Europe, Ontario or Australia. Clonality appeared high in Western Canada, possibly because environmental conditions there were less conducive to sexual reproduction. Leptosphaeria maculans is a model invasive pathogen with contrasting features in different regions: shallow population structure, high genetic variability and regular sexual recombination in some regions, by comparison with reduced genetic variability, high rates of asexual multiplication, strong population structure or admixture in others.

病原菌侵入全新区域后，可引发新型植物真菌病害。解析真菌病原菌的起源、传播途径、生殖系统潜在变化及种群规模动态，对于制定这类病害的综合防控策略至关重要。本研究利用小卫星标记（minisatellite markers），对引起油料与蔬菜芸薹属作物茎溃疡（黑胫病）的植物病原真菌黑胫茎点霉（Leptosphaeria maculans）的全球入侵历史进行了解析。聚类分析将该病原菌的基因型划分为对应主要地理区域的不同种群，同时在加拿大西部发现了两个分化显著的种群。基于近似贝叶斯计算（Approximate Bayesian Computation）的入侵场景比对分析显示，该病原菌起源于疫情首次被记录的美国，且在近数十年间从美国独立传入加拿大东部（安大略省）、欧洲与澳大利亚。加拿大西部的种群似乎起源于安大略省的种群，而智利的种群则由多个来源的菌株混合形成。研究推断，传入加拿大西部的过程存在种群瓶颈效应，而传入欧洲、安大略省或澳大利亚的过程则未出现该效应。加拿大西部种群的无性繁殖占比极高，这可能是因为当地环境条件不利于有性生殖。黑胫茎点霉（Leptosphaeria maculans）是典型的入侵性病原真菌，不同区域的种群呈现出截然相反的特征：部分区域的种群具有较浅的种群结构、较高的遗传多样性与规律的有性重组；而另一部分区域的种群则表现为遗传多样性降低、无性繁殖率高、种群结构显著或存在混合起源。