从类似纹枯病的水稻病株上分离到一种在菌核形态上与纹枯病菌(Rhizoctonia solani)有明显差异的真菌,致病性测定结果表明该菌能侵染水稻、玉米和大豆。对该菌的显微形态、生物学特性以及核糖体DNA-ITS序列进行研究,结果表明该菌为嗜水小核菌(Sclerotium hydrophilum Sacc.)。病菌在30℃、pH为6~9条件下生长表现最佳,属硫胺素自养型菌;营养菌丝与立枯丝核菌相似,菌核球形或椭圆形,数量极多,其平均大小仅为386.4μm×420.7μm;该菌的核糖体DNA-ITS序列与GenBank中唯一一个嗜水小核菌(登录号为DQ875597)的同源性为99.5%,并且与大多数丝核菌(Rhizoctonia spp.)也有一定的同源性,病菌的28S rDNA-RFLP分析结果进一步说明了该菌在系统发育上与丝核菌类真菌具有较高的同源性。通过比较该菌和几种与水稻纹枯病相关丝核菌核糖体DNA-ITS序列的差异,设计了一对特异性引物PS-1和PS-2,能专一地从被该菌侵染的水稻感病组织中扩增出一段约550bp的DNA。

A fungus was isolated from diseased rice in Guangxi,and the pathogenicity test indicated that its isolates could infect rice,corn and soybean under certain conditions.Based on microscopic morphology,other biological characteristics and ribosomal DNA-ITS sequence,the isolates obtained were identified as Sclerotium hydrophilum Sacc.,had an optimum temperature for hyphal growth at 30℃ and an optimal pH 6-9 in the culture media,and were prototrophic for thiamine.Its vegetative mycelia were similar to that of Rhizoctonia spp.The sclerotia,round and oval in shape,formed on the surface of PDA;the size of individual sclerotium was 386.4 μm×420.7 μm.Its sequence of ribosomal DNA-ITS was similar to that of S.hydrophilum(GenBank accession number:DQ875597) with 99.5% identity,and showed high homology with the strains of Rhizoctonia spp.,which was further demonstrated by the restriction analysis of an amplified fragment from 28S ribosomal DNA of these species.One specific primer pair,PS-1/PS-2,was designed from the sequence of ribosomal DNA-ITS of S.hydrophilum based on the conserved sequence determined by alignment with those of Rhizoctonia spp.By using this primer pair PS-1/PS-2,a band of 550 bp was amplified from S.hydrophilum but not from Rhizoctonia spp.