ABSTRACT

Gaeumannomyces graminis var. graminis (Ggg) has been the etiological agent of take-all root rot (TARR) in St. Augustinegrass (Stenotaphrum secundatum) and root decline of the other warm-season turfgrasses. Seventy-five Ggg isolates were obtained from St. Augustinegrass in central and east Texas. Evaluation of colony morphologies on potato dextrose agar (PDA) within 2 wk and follow-up multilocus phylogenic analyses revealed three phenotypic groups associated with different Gaeumannomyces species: (i) G. floridanus, highly melanized with round colony formation; (ii) G. arxii, none to slightly melanized with round colony formation; and (iii) G. graminicola, highly melanized with irregular colony formation. Further examination with representative isolates from each group revealed that their phenotypic characterizations supported the distinctive genetic groups within Ggg associated with St. Augustinegrass TARR. Gaeumannomyces floridanus isolates grew faster at warmer temperature (30 C) than G. arxii or G. graminicola. Pathogenicity assays using rice seedlings indicated that G. floridanus was more aggressive in disease symptom development than G. arxii or G. graminicola. A multilocus phylogeny reconstruction supported that most of Gaeumannomyces isolates tested in this study were separated into three phylogenetically distinct groups: G. floridanus, G. arxii, and G. graminicola. The resolution of intravarietal complexities of causal fungi of TARR is important for proper diagnostics and management strategies for TARR in St. Augustinegrass and other root-decline diseases in warm-season turfgrasses.

摘要

Gaeumannomyces graminis变种。禾本科( Ggg ) 是圣奥古斯丁草( Stenotaphrum secundatum ) 全根腐烂 (TARR ) 和其他暖季草坪草根部衰退的病原体。从德克萨斯州中部和东部的 St. Augustinegrass 中获得了75 个Ggg分离株。2 周内对马铃薯葡萄糖琼脂 (PDA) 菌落形态的评估和后续多位点系统发育分析揭示了与不同Gaeumannomyces物种相关的三个表型组： (i) G. floridanus，高度黑色化，形成圆形菌落；(ii) G. arxii，无至轻微黑色化，形成圆形菌落；(iii)G. graminicola，高度黑化，形成不规则菌落。对来自每个组的代表性分离株的进一步检查表明，它们的表型特征支持与圣奥古斯丁草TARR 相关的Ggg内独特的遗传组。Gaeumannomyces floridanus分离株在较高温度（30°C）下比G. arxii或G. graminicola生长得更快。使用水稻幼苗的致病性测定表明，G. floridanus在疾病症状发展方面比G. arxii或G. graminicola更具侵略性。多位点系统发育重建支持大多数Gaeumannomyces在本研究中测试的分离物分成三个系统发育上不同的组：G. floridanus，G. arxii，和G ^。禾本科。解决 TARR 致病真菌的品种内复杂性对于正确诊断和管理圣奥古斯丁草中的 TARR 和暖季草坪草中的其他根衰病病很重要。