Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America.
West Central Research and Extension Center, University of Nebraska, North Platte, Nebraska, United States of America.
PLoS One. 2021 Apr 27;16(4):e0249335. doi: 10.1371/journal.pone.0249335. eCollection 2021.
The Sandhills of Nebraska is a complex ecosystem, covering 50,000 km2 in central and western Nebraska and predominantly of virgin grassland. Grasslands are the most widespread vegetation in the U.S. and once dominated regions are currently cultivated croplands, so it stands to reason that some of the current plant pathogens of cultivated crops originated from grasslands, particularly soilborne plant pathogens. The anamorphic genus Rhizoctonia includes genetically diverse organisms that are known to be necrotrophic fungal pathogens, saprophytes, mycorrhiza of orchids, and biocontrol agents. This study aimed to evaluate the diversity of Rhizoctonia spp. on four native grasses in the Sandhills of Nebraska and determine pathogenicity to native grasses and soybean. In 2016 and 2017, a total of 84 samples were collected from 11 sites in the Sandhills, located in eight counties of Nebraska. The samples included soil and symptomatic roots from the four dominant native grasses: sand bluestem, little bluestem, prairie sandreed, and needle-and-thread. Obtained were 17 Rhizoctonia-like isolates identified, including five isolates of binucleate Rhizoctonia AG-F; two isolates each from binucleate Rhizoctonia AG-B, AG-C, and AG-K, Rhizoctonia solani AGs: AG-3, and AG-4; one isolate of binucleate Rhizoctonia AG-L, and one isolate of R. zeae. Disease severity was assessed for representative isolates of each AG in a greenhouse assay using sand bluestem, needle-and-thread, and soybean; prairie sandreed and little bluestem were unable to germinate under artificial conditions. On native grasses, all but two isolates were either mildly aggressive (causing 5-21% disease severity) or aggressive (21-35% disease severity). Among those, three isolates were cross-pathogenic on soybean, with R. solani AG-4 shown to be highly aggressive (86% disease severity). Thus, it is presumed that Rhizoctonia spp. are native to the sandhills grasslands and an emerging pathogen of crops cultivated may have survived in the soil and originate from grasslands.
内布拉斯加州沙丘是一个复杂的生态系统，覆盖了内布拉斯加州中部和西部的 50,000 平方公里，主要是原始草原。草原是美国分布最广泛的植被，曾经占据主导地位的地区现在是耕种的农田，因此可以合理地认为，一些目前用于栽培作物的植物病原菌起源于草原，特别是土壤传播的植物病原菌。形态上的 Rhizoctonia 属包括遗传上多样化的生物体，已知它们是坏死真菌病原体、腐生物、兰花的菌根和生物防治剂。本研究旨在评估内布拉斯加州沙丘四种本地草上 Rhizoctonia spp. 的多样性，并确定其对本地草和大豆的致病性。2016 年和 2017 年，共从内布拉斯加州八个县的 11 个地点收集了 84 个样本。这些样本包括来自四种主要本地草的土壤和有症状的根：沙蓝茎草、小蓝茎草、草原沙草和针线草。共获得了 17 个类似 Rhizoctonia 的分离物，包括 5 个双核 Rhizoctonia AG-F 分离物；双核 Rhizoctonia AG-B、AG-C 和 AG-K 各 2 个分离物、Rhizoctonia solani AGs：AG-3 和 AG-4；一个双核 Rhizoctonia AG-L 分离物和一个 R. zeae 分离物。在温室试验中，使用沙蓝茎草、针线草和大豆对每个 AG 的代表性分离物进行了疾病严重程度评估；草原沙草和小蓝茎草在人工条件下无法发芽。在本地草上，除了两个分离物外，所有分离物都表现出轻度侵袭性（导致 5-21%的疾病严重程度）或侵袭性（21-35%的疾病严重程度）。其中，有三个分离物对大豆具有交叉致病性，R. solani AG-4 表现出高度侵袭性（86%的疾病严重程度）。因此，可以假定 Rhizoctonia spp. 是沙丘草原的本地物种，而在土壤中存活下来的作物栽培的新兴病原体可能起源于草原。
