Population structure and genetic diversity of Fusarium graminearum from southwestern Russia and the Russian Far East as compared with northern Europe and North America

Genetic variation at variable number tandem repeat (VNTR) markers was used to assess population structure and diversity among 296 Fusarium graminearum isolates from northern Europe (Finland, northwestern Russia, and Norway), southern Europe (southwestern and western Russia), and Asia (Siberia and the Russian Far East). We identified at least two highly differentiated and geographically structured genetic populations (E1 and E2) in Eurasia (ΦPT = 0.35). Isolates from northern Europe were almost exclusively from the E1 population (95.6%) and had the 3ADON (3-acetyldeoxynivalenol) trichothecene genotype (97.3%). In contrast, all isolates from southern Europe were from the E2 population and 94.4% had the 15ADON (15-acetyldeoxynivalenol) genotype. The E2 population also predominated in the Asian sampling locations (92.7%) where 3ADON and 15ADON genotypes occurred at nearly equal frequencies. Southern European isolates were more closely related to those from Asia (ΦPT = 0.06) than to geographically closer populations from northern Europe (ΦPT ≥ 0.31). Northern European populations also harbored substantially less genetic diversity (Ne ≤ 2.1) than populations in southern Europe or Asia (Ne ≥ 3.4), indicative of a selective sweep or recent introduction and subsequent range expansion in northern Europe. Bayesian analyses incorporating previously described genetic populations from North America (NA1 and NA2) surprisingly identified NA2 and E2 as a single genetic population, consistent with hypotheses of a recent Eurasian origin for NA2. Additionally, more than 10% of the isolates from Asia and southern Europe were assigned to the NA1 population, indicating recent introductions of NA1 into parts of Eurasia. Collectively, these results demonstrate that there are at least three genetic populations of F. graminearum in the Northern Hemisphere and indicate that population-level diversity in Eurasia and North America has been shaped by recent transcontinental introductions.本研究采用可变数目串联重复序列（variable number tandem repeat, VNTR）标记的遗传变异，对来自北欧（芬兰、俄罗斯西北部、挪威）、南欧（俄罗斯西南部及西部）以及亚洲（西伯利亚与俄罗斯远东地区）的296株禾谷镰孢菌（Fusarium graminearum）分离株的种群结构与遗传多样性进行分析。研究团队在欧亚大陆中鉴定出至少两个高度分化且具有地理结构的遗传种群（E1与E2），其ΦPT统计量为0.35。北欧来源的分离株几乎全部属于E1种群（占比95.6%），且97.3%的分离株携带3-乙酰脱氧雪腐镰刀菌烯醇（3-acetyldeoxynivalenol, 3ADON）单端孢霉烯族毒素基因型。与之相反，南欧来源的所有分离株均属于E2种群，其中94.4%携带15-乙酰脱氧雪腐镰刀菌烯醇（15-acetyldeoxynivalenol, 15ADON）基因型。E2种群在亚洲采样区域中也占据主导地位（占比92.7%），该区域内3ADON与15ADON基因型的检出频率近乎相等。南欧分离株与亚洲分离株的亲缘关系更为紧密（ΦPT=0.06），而非地理距离更近的北欧种群（ΦPT≥0.31）。北欧种群的遗传多样性水平显著低于南欧或亚洲种群（有效种群数量Ne≤2.1，而后者Ne≥3.4），这一结果提示北欧种群曾经历选择性清除，或是近期被引入并随后发生了范围扩张。结合此前已报道的北美遗传种群（NA1与NA2）进行贝叶斯分析后，研究人员意外发现NA2与E2实为同一个遗传种群，这一结果与“NA2种群近期起源于欧亚大陆”的假说相符。此外，亚洲与南欧来源的分离株中有超过10%被划归为NA1种群，这表明NA1种群近期被引入到欧亚大陆的部分区域。综合来看，本研究结果证实北半球中至少存在三个禾谷镰孢菌的遗传种群，同时表明欧亚大陆与北美的种群水平多样性是由近期的跨大陆种群引入事件所塑造的。