Isolation, Identification And Pathotypes Of Phytophthora Sojae In Anhui Province

Phytophthora root rot is a quarantinable and destructive disease,which puts great threat to soybean.In the areas of Huaibei and Huaihe Basin in Anhui province,root rot disease appears widely in the middle-late growth stage of summer soybean in recent years.The 43 strains of Phytophthora sojae,which were isolated from the 471 soil samples in the main producing areas of Anhui summer soybean and the diseased plants collected in Guoyang,Huaiyuan and Guzhen of Anhui Province,contained 3 isolates from the diseased plants.The results of soil samples isolation showed that Phytophthora sojae actually existed in different soil samples and strains of P.sojae were more easily isolated from the samples collected from Guoyang,Huaiyuan and Guzhen.Six representative isolates,which were GY4,HY16,GZ10 isolated from soybean soil samples and GY8,HY11,GZ21 isolated from diseased soybean plants,were selected for identification further.The morphological characteristics,pathogenicity to soybean seedlings and ribosomal DNA-ITS sequences were investigated respectively.The results showed that on LBA plates,the colonies of all the six isolates were white and round,with uniform texture.The hyphae were septumless and dense,with nearly right-angled branches.In 10% V8 broth,the sporangia were non-papillate,acrogenous,not deciduous,oviform to ellipsoidal,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.On LBA,ogonia were spherical or nearly spherical,and antheridia were mostly paragynous.The soybean seedlings of Hefeng 35 showed the typical symptom of Phytophthora root rot after being inoculated with the isolates.The sequences of ribosomal DNA-ITS of these isolates were closest relative to that of P.sojae published in GenBank with 100% identity.Based on the morphological characteristics,pathogenicity and molecular identification,the six strains were identified as P.sojae.The pathotypes of 43 isolates were identified respectively by adopting differential hosts with certain anti-disease gene.The experimental results showed that 43 strains belonged to 38 different pathotypes.The pathogenic types with the highest frequency were3 c,4,6,7,which accounted for 9.30% of the total number of strains;2 stains could overcome 10 anti-disease genes,and 3 strains could overcome 9 anti-disease genes.Therefore,it can be concluded that there were some highly toxic strains of P.sojae in the main producing areas in Anhui Province.The strains overcoming Rps1 c were the least ones,a frequency of 2.33%.And the frequency of strains to overcome Rps1 a and Rps1 k was below 10%.The strains that could overcome Rps5 and Rps7 are the most,and the frequency was 65.12%.Then the frequency of strains that can overcome Rps3 a,Rps3b,Rps3 c,Rps4 and Rps6 was more than 50%,and their use in breeding was greatly reduced.The maximum amount of strains were strains with Avr-1c,the frequency was up to 97.67%.And the frequency of strains with Avr-1a,Avr-1k was more than 90%.These three types have high value in breeding.