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.

病原菌传入新区域可引发植物新型真菌病害。明晰植物病原真菌的起源、传入路径、生殖系统潜在变化及种群规模，是制定这类病害综合防控策略的必要前提。本研究采用小卫星标记（minisatellite markers），解析了引起油料与蔬菜十字花科作物茎溃疡（黑胫病，stem canker (blackleg)）的油菜茎基溃疡病菌（Leptosphaeria maculans）的全球入侵历史。聚类分析将基因型划分为对应主要地理区域的独立种群，同时在加拿大西部区分出两个分化种群。通过近似贝叶斯计算（Approximate Bayesian Computation）对多种入侵场景进行比较分析，结果表明该病原菌起源于美国——这也是疫情首次被记录的区域，且在过去数十年间从该区域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源种群，而智利的种群则由多个源种群混合形成。研究推断，加拿大西部的种群在传入过程中经历了种群瓶颈效应，而欧洲、安大略省与澳大利亚的种群则未出现该效应。加拿大西部种群的无性繁殖特征显著，这可能是因为当地环境更不利于有性生殖的进行。油菜茎基溃疡病菌（Leptosphaeria maculans）是一类具有区域差异化特征的模式入侵病原菌：部分区域的种群结构浅显、遗传变异度高且存在规律的有性重组；与之相对，其他区域的种群则表现为遗传变异度降低、无性繁殖率高、种群结构分化显著或存在种群混合现象。