Isolation And Identification Of Phytophtjora Sojae In Suzhou Of Anhui Province

The soybean blight,also called Phytophthora root rot of soybean,is caused by Phytophthora sojae.It is one of the most serious diseases on soybean production.Based on the isolation of the causal organism of soybean Phytophthora root rot from Suzhou area,the identification of Phytophthora sojae using the method of morphology and pathogenicity tests,and sequencing of ribosomal DNA-ITS of the isolates were studied systematically in the dissertation.The main results are as follows.The 50 soil samples in soybean fields were collected from the main soybean producing areas of Suzhou area in Anhui province,and Phytophthora sojae was detected by the method of soybean leaf-disc baiting.The result indicated that P.sojae has been baited from 2 soil samples and the frequency of isolate separation was 4%.Two isolates which separated from soybean fields were identified via the method of morphology and the pathogenicity test with hypocotyl wound inoculation.The results showed that hyphae were nonseptate,with almost rectangular branch and branch bases constricted,swellings could be formed,diameter at 3.1~9.6?m with the average to be 5.05?m.Sporangia were acrogenous,non-papillate,and not deciduous in water.The internal proliferation of sporangia could be observed.Sporangia were inverted-pear-shaped,measuring 21.2~85.3 ? 16.3~32.6 ?m(averagely 44.99 ? 27.94 ?m),with lenth / breadth ratio(L/B)of 1.61.The isolates were homothallic.Rounded Oogonia were spherical with the diameters at 27.3~48.7?m,averagely 36.49 ?m.Oospores were spherical,yellowish,with the diameters at 20.3~41.2?m,averagely 36.49 ?m.Antheridia were mostly paragynous,occasionally amphigynous,measuring 13.22(5.60~18.10)?m × 11.14(5.90~15.30)?m.Refer to the major Phytophthora classification key table,the isolates were identified as Phytophthora sojae.Two isolates were pathogenic to Hefeng 35 soybean seedlings,and the symptoms caused by wound inoculation were the same as naturally infected soybean plants.The two isolates were identified as Phytophthora sojae according to Koch's rules.The isolates were inoculated on different resistance genes of 15 soybean varieties by using hypocotyls' inoculation method on the basis of the above.The experimental results showed that 2 isolates belonged to different pathotypes.The pathotypes of SZ1 were3 c,4,5,6,7;the pathotypes of.SZ5 were 1b,d,3a,3b,4,5,7,8.Polymerase chain reaction(PCR)products from the internal transcribed spacer(ITS)regions of the ribosomal DNA of two P.sojae isolates using the specificity primers were amplified.The results showed that a single band of PCR product about 300 bp was amplified from above two tested isolates.Sequences from the above isolates were compared with published sequences of P.sojae(Accession No: FJ545233,GU993914 and HQ643349)were produced based on ITS sequence data by Unweighted Pair-Group Method with Arithmetic Means methods of the software Mega and Clustalx.The results indicated that all the two base sequences of ITS were equal length,and the nucleotide sequence was identical with the above published sequences of P.sojae in GenBank.Two strains could prove to be P.sojae therefore.