Identification And Study Of Characteristics Of Several Kinds Of Sclerotium-Froming Fungal Strains From Rice

Rice sheath blight is one of the most destructive diseases of rice and make greatlosses every year. The pathogen of rice sheath blight includes Rhizoctonia solani Kuhn,Rhizoctonia oryzae, and Rhizoctonia oryzae-sativae. Ten sclerotium-producing fungalstrains isolated from lesions of rice sheath blight show various characteristics on PDA. Inthis paper, the biological and genetic diversity of these strains were studied. Our resultshere may supply information about pathogen of rice sheath blight.The results showed that there are three main types of distribution of sclerotia inPetri dish: random distribution (rcol, wh-68, wh-79, B-10, and wh-81), centraldistribution (wh-87, wh-81, and wh-62), edgewise distribution (wh-1 and wh-94). Strainswh-1 and wh-94 were multinucleated. Strain wh-87, wh-81, wh-90, wh-62 wh-68, wh-79,and B-10 were binucleated. Strain Rcol was miscellaneous nuclear, most cells weremultinucleated, while part cells were binucleated and even mononucleated. Hyphaediameter of wh-1 and wh-94 was significantly greater than that of wh-87, wh-81, wh-90,wh-62 and other binucleated strains. There was significant difference of virulence amongdifferent strains. Wh-1 and wh-94 had the strongest virulence. All strains had the fastestgrowth rate in pH 6.0-7.0, 25℃-30℃. The growth rate was faster in czapek solidmedium containing starch, proline, ammonium sulfate acid, glycine, and alanine. Thegrowth was the slowest in czapek containing lactose and lysine. In the most appropriatesource of carbon, nitrogen conditions, all strains display almost the same growth rate, thenumber of sclerotia, and the dry weight of sclerotia.Wh-68, wh-79, and B-10 produced sclerotia of micro-needle size. In order to identifythese strains, ITS and 18S rDNA of wh-68 were amplified and sequenced. Wh-68 wasidentified as Sclerotium hydrophilum Sacc according to the sequences of rDNA.Genetic diversity of these strains was analyized by using of RAPD technology. TheRAPD reaction system was established. Sixty-two from 100 (s300-s399, Shanghaisangon) had been obtained as band-rich primers. Seven strains were divided into 2 groupsaccording to the results of RAPD amplification by the 62 primers: the first group includedstrains wh-1 and wh-94. The second group consists of two sub-groups, namely Rcol,wh-87 sub-group and wh-62, wh-81, wh-90 sub-group.Strain Rcol contains two types of ITS, namely most are Ceratobasidium oryzae-sativae AG-Bb ITS, while parts are Thanatephorus cucumeris AG-1-IA ITS. A bandcould be amplified specific to wh-94 (Thanatephorus) and Rcol, while not existing in wh-87 (Ceratobasidium) by using s393 as RAPD primer. Sequence of this fragmentwas partial of 18S rDNA sharing high identity with that of Thanatephorus sp. Thisresult supply further proof to the fact that Rcol may be an hybrid strain of Ceratobasidiumsp. and Thanatephorus sp.