Identification and rDNA-ITS sequence analysis of the pathogen of soybean Phytophthora root rot in Anhui Province
In order to determine the pathogen of Phytophthora root rot on summer soybean in Anhui Province,the diseased samples from plants and soil were collected from Guoyang,Huaiyuan and Guzhen counties on soybean field.Six representative isolates were selected for identification after isolation and purification of the pathogen.The morphological characteristics,pathogenicity to soybean seedlings and ribosomal DNA-ITS sequences analysis were investigated with morphological observation.The results showed that the colonies of all the six isolates on LBA plates were white and round with uniform texture.The hyphae were nonseptate and dense with nearly right-angled branches.In 10％ V8C broth,the sporangia were non-papillate,acrogenous,not deciduous,oviform to ellipsoidal and non-papillate with length/breadth ratios (L/B) over 1.6 ∶ 1.Internal proliferation of sporangia could be observed.All isolates were homothallic with sexual organs abundant in single cultures.Oogonia were spherical or nearly spherical,and antheridia were mostly paragynous on LBA plates.The soybean seedlings of Hefeng 35 inoculated with the isolates showed the typical symptom of Phytophthora root rot.The sequences of ribosomal DNA-ITS of the six isolates were closest relative to that of Phytophthora sojae with 100％ identity.The virulence formulas of GY4,GY8,HY11,HY16,GZ10,GZ21 were 1b,2,3a,3b,4,5,6,7;1b,1d,3a,3b;1d,3a,3b,3c,4,5,6,7;2,3c,4,5,6,7;1b,3a,3c,5,8;3a,3b,5,6,7,8,respectively,and the six strains belonged to six different pathotypes.The results indicated that the six strains were identified as P.sojae.
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