Phytopathology. 2002 Sep;92(9):946-55. doi: 10.1094/PHYTO.2002.92.9.946.
ABSTRACT The genetic structure of field populations of Mycosphaerella graminicola was determined across a hierarchy of spatial scales using restriction fragment length polymorphism markers. The hierarchical gene diversity analysis included 1,098 isolates from seven field populations. Spatial scales ranged from millimeters to thousands of kilometers, including comparisons within and among lesions, within and among fields, and within and among regions and continents. At the smallest spatial scale, microtransect sampling was used to determine the spatial distribution of 15 genotypes found among 158 isolates sampled from five individual lesions. Each lesion had two to six different genotypes including both mating types in four of the five lesions, but in most cases a lesion was composed of one or two genotypes that occupied the majority of the lesion, with other rare genotypes interspersed among the common genotypes. The majority (77%) of gene diversity was distributed within plots ranging from approximately 1 to 9 m(2) in size. Genotype diversity (G / N) within fields for the Swiss, Texas, and Israeli fields was high, ranging from 79 to 100% of maximum possible values. Low population differentiation was indicated by the low G(ST) values among populations, suggesting a corresponding high degree of gene flow among these populations. At the largest spatial scale, populations from Switzerland, Israel, Oregon, and Texas were compared. Population differentiation among these populations was low (G(ST) = 0.05), and genetic identity between populations was high. A low but significant correlation between genetic and geographic distance among populations was found (r = -0.47, P = 0.012), suggesting that these populations probably have not reached an equilibrium between gene flow and genetic drift. Gene flow on a regional level can be reduced by implementing strategies, such as improved stubble management that minimize the production of ascospores. The possibility of high levels of gene flow on a regional level indicates a significant potential risk for the regional spread of mutant alleles that enable fungicide resistance or the breakdown of resistance genes.
摘要 使用限制片段长度多态性标记，在一个层次结构的空间尺度上，确定了无性型叶点霉田野种群的遗传结构。层次基因多样性分析包括来自 7 个田野种群的 1098 个分离物。空间尺度从毫米到数千公里不等，包括病变内和病变间、田间内和田间间、以及区域和大陆内和间的比较。在最小的空间尺度上，使用微横切采样来确定在从五个病变中取样的 158 个分离物中发现的 15 个基因型的空间分布。每个病变有 2 到 6 个不同的基因型，包括四个病变中的两个交配型，但在大多数情况下，一个病变由一个或两个占据病变大部分的基因型组成，其他稀有基因型散布在常见基因型之间。77%的基因多样性分布在大小约为 1 到 9 平方米的斑块内。瑞士、德克萨斯和以色列田间的基因型多样性（G/N）很高，范围在最大可能值的 79%到 100%之间。种群间低的 G(ST)值表明种群间存在相应的高度基因流，表明种群间的分化程度很低。在最大的空间尺度上，比较了来自瑞士、以色列、俄勒冈和德克萨斯的种群。这些种群之间的种群分化程度很低（G(ST)=0.05），种群间的遗传相似性很高。发现种群间遗传和地理距离之间存在低但显著的相关性（r=-0.47，P=0.012），这表明这些种群可能尚未达到基因流和遗传漂变之间的平衡。通过实施改进茬管理等策略，可以减少区域水平上的基因流，从而最大限度地减少子囊孢子的产生。区域水平上的高基因流可能性表明，具有杀菌剂抗性或抗性基因失效的突变等位基因在区域内传播的风险显著。
