Department of Plant Pathology and Microbiology, University of California, Riverside 92521, USA.
Phytopathology. 2011 Jan;101(1):85-91. doi: 10.1094/PHYTO-08-10-0205.
Gray leaf spot (GLS) disease of perennial ryegrass (Lolium perenne) and kikuyugrass (Pennisetum clandestinum) in golf courses in California was first noted in 2001 and 2003, respectively, and within 5 years had become well established. The causal agent of the disease is the fungus Magnaporthe grisea, which is known to consist primarily of clonal lineages that are highly host specific. Therefore, our objective was to investigate host specificity and population dynamics among isolates associated primarily from perennial ryegrass and kikuyugrass since the disease emerged at similar times in California. We also obtained isolates from additional hosts (tall fescue, St. Augustinegrass, weeping lovegrass, and rice) and from the eastern United States for comparative purposes. A total of 38 polymorphic amplified fragment length polymorphism makers were scored from 450 isolates which clustered by host with high bootstrap support (71 to 100%). Genetic structure between kikuyugrass and perennial ryegrass isolates differed significantly. Isolates from kikuyugrass were genotypically diverse (n = 34), possessed both mating types, and some tests for random mating could not be rejected, whereas isolates from perennial ryegrass were less genotypically diverse (n = 10) and only consisted of a single mating type. Low genotypic diversity was also found among the other host specific isolates which also only consisted of a single mating type. This is the first study to document evidence for the potential of sexual reproduction to occur in M. grisea isolates not associated with rice (Oryza sativa). Moreover, given the significant host specificity and contrasting genetic structures between turfgrass-associated isolates, the recent emergence of GLS on various grass hosts in California suggests that potential cultural practices or environmental changes have become conducive for the disease and that the primary inoculum may have already been present in the state, despite the fact that two genotypes associated with perennial ryegrass and St. Augustinegrass in California were the same as isolates collected from the eastern United States.
加利福尼亚州高尔夫球场中的多年生黑麦草（Lolium perenne）和肯塔基蓝草（Pennisetum clandestinum）的灰叶斑病分别于 2001 年和 2003 年首次被发现，且在 5 年内已广泛存在。该病害的病原菌是稻瘟病菌（Magnaporthe grisea），其主要由高度宿主特异性的克隆谱系组成。因此，我们的目标是研究与主要来自多年生黑麦草和肯塔基蓝草的分离物相关的宿主特异性和种群动态，因为该病害在加利福尼亚州同时出现。我们还从其他宿主（高羊茅、海滨雀稗、垂序马唐和水稻）和美国东部获得了分离物，以进行比较。我们从 450 个分离物中获得了 38 个多态性扩增片段长度多态性标记，这些标记根据宿主聚类，支持度很高（71%到 100%）。肯塔基蓝草和多年生黑麦草分离物之间的遗传结构存在显著差异。肯塔基蓝草分离物的基因型多样性丰富（n = 34），具有两种交配型，有些随机交配测试不能被拒绝，而多年生黑麦草分离物的基因型多样性较低（n = 10），且只具有单一交配型。其他宿主特异性分离物的基因型多样性也较低，也只具有单一交配型。这是首次记录稻瘟病菌分离物可能在不与水稻（Oryza sativa）相关的情况下发生有性繁殖的证据。此外，鉴于草坪草相关分离物具有显著的宿主特异性和不同的遗传结构，加利福尼亚州各种草类宿主上最近出现的灰叶斑病表明，潜在的文化实践或环境变化可能有利于该病害，而且主要的接种体可能已经存在于该州，尽管加利福尼亚州的两种与多年生黑麦草和海滨雀稗相关的基因型与从美国东部收集的分离物相同。
