<i>Gaeumannomyces nanograminis</i>, sp. nov., a hyphopodiate fungus identified from diseased roots of ultradwarf bermudagrass in the United States
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The genus <i>Gaeumannomyces</i> (Magnaporthaceae, Magnaporthales, Sordariomycetes, Ascomycota) includes root-infecting pathogens, saprobes, and endophytes. Morphological, biological, and phylogenetic analyses were employed to identify fungal isolates derived from turfgrass roots colonized with ectotrophic, dark runner hyphae. Phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions and of the minichromosome maintenance complex 7 (<i>MCM7</i>), largest subunit of RNA polymerase II (<i>RPB1</i>), and translation elongation factor 1-alpha (<i>TEF1</i>) genes were obtained via maximum likelihood and Bayesian methods. Our isolates consistently formed a distinct and highly supported clade within <i>Gaeumannomyces</i>. Common and distinctive biological and morphological characters reinforced these findings. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass (<i>Cynodon dactylon</i> (L.) Pers. × <i>C. transvaalensis</i> Burtt-Davey), its native host, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, <i>Gaeumannomyces nanograminis</i>, associated with rotted roots of ultradwarf bermudagrass.
顶囊壳属（Gaeumannomyces）隶属于子囊菌门（Ascomycota）粪壳菌纲（Sordariomycetes）马格南孢目（Magnaporthales）马格南孢科（Magnaporthaceae），该类群包含侵染根系的病原菌、腐生真菌及内生真菌。本研究通过形态学、生物学及系统发育分析，对从被外生暗色匍匐菌丝定殖的草坪草根系中分离得到的真菌菌株开展鉴定工作。研究选取18S核核糖体DNA（18S nuc rDNA）、ITS1-5.8S-ITS2核核糖体DNA内部转录间隔区、28S核核糖体DNA区域的部分序列，以及微型染色体维持复合体7（MCM7）、RNA聚合酶II最大亚基（RPB1）、翻译延伸因子1-α（TEF1）基因的序列，采用最大似然法与贝叶斯法构建系统发育树。结果显示，本研究分离得到的菌株在顶囊壳属内始终形成一个独立且支持度极高的演化支，共有与特有的生物学及形态学特征进一步佐证了上述结论。此外，本研究开展了致病性评价，证实该真菌可通过外生暗色匍匐菌丝定殖其天然寄主超矮型狗牙根（Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey）的根系，并引发根系变色、根系及地上部生物量降低等病害症状。综上，本研究明确了该新物种的分类地位并对其进行描述，该新物种为纳米顶囊壳（Gaeumannomyces nanograminis），与超矮型狗牙根的腐烂根系相关。
