Leptosphaerulina species isolated from golf turfgrass in China, with description of L. macrospora, sp. nov.

Leptosphaerulina leaf blight occurs on most turfgrasses. Hitherto, Leptosphaerulina species associated with this disease include L. americana, L. argentinensis, L. australis, and L. trifolii. However, following Koch’s postulates, L. australis was confirmed as saprobes but not pathogens, and the other three species have not been tested. The pathogenicity of Leptosphaerulina spp. is still questionable. In this study, we isolated 19 Leptosphaerulina strains from diseased golf turfgrasses in China, and they were identified as L. gaeumannii, L. saccharicola, and a new species, L. macrospora, through multilocus (ITS, 28S, rpb2, and tub2) phylogenetic analyses and morphological observations. Pathogenicity test revealed that the three Leptosphaerulina species identified in this study cannot infect live/healthy turfgrass tissues of Poa pratensis and Agrostis stolonifera and only produced pseudothecia on the dead leaves of stressed seedlings. Considering the results of pathogenicity tests in this and previous studies, we speculate that most Leptosphaerulina species isolated from diseased turfgrass are not pathogens but saprobes. Applying proper management practices to prevent severe turfgrass stress is a key measure to reduce or eliminate the effects of Leptosphaerulina on golf turfgrass.小球腔菌叶枯病可侵染多数草坪草。迄今为止，与该病害相关的小球腔菌属物种包括美洲小球腔菌（L. americana）、阿根廷小球腔菌（L. argentinensis）、澳大利亚小球腔菌（L. australis）以及三叶草小球腔菌（L. trifolii）。然而，经科赫法则（Koch's postulates）验证后，澳大利亚小球腔菌被证实为腐生菌而非病原菌，其余三个物种尚未开展相关检测。小球腔菌属物种的致病性仍存在争议。 本研究从中国患病高尔夫球场草坪草中分离得到19株小球腔菌属菌株，通过多位点（ITS、28S、rpb2及tub2）系统发育分析与形态学观察，将其鉴定为盖曼小球腔菌（L. gaeumannii）、糖生小球腔菌（L. saccharicola）以及新物种大孢小球腔菌（L. macrospora）。致病性测试结果显示，本研究鉴定出的三种小球腔菌属菌株无法侵染草地早熟禾（Poa pratensis）与匍匐翦股颖（Agrostis stolonifera）的活/健康草坪草组织，仅在胁迫幼苗的枯死叶片上形成假囊壳。 综合本研究与既往研究的致病性测试结果，我们推测，从患病草坪草中分离得到的多数小球腔菌属物种并非病原菌，而是腐生菌。采取合理管理措施以减轻草坪草的严重胁迫，是降低或消除小球腔菌属物种对高尔夫球场草坪草危害的核心手段。