Isolation, Identification And Pathotypes Of Phytophthora Sojae From Anhui Province

The 47 strains of Phytophthora were isolated from 487 soil samples in soybean field collected from the main soybean-producing areas in Anhui Province by useing soil leaf discs trapping methods under the action of the fungicide. Of them,18 strains were isolated from the 88 soil samples from Taihe County, with the frequency of strains isolated as 20.45%. From 57 soil samples in Guoyang County,14 strains were isolated, with the frequency of stains isolated as 24.56%. And from 43 soil samples of Guzhen,7 strains were isolated, with the frequency of strains isolated as 16.28%. The average frequency of strains isolated was 9.65%.Three representative strains (TH4, GY65, GZ6) selected from the 47 strains were identified by applying morphology and hypocotyl wound inoculation and pathogenicity test methods, respectively. The results showed that the main hyphae were nonseptate with almost right branchs. The hyphal diameters were 2.3-6.4μm. Hyphal swellings could be formed sometimes. Sporangia were mostly terminal, ellipsoid to obpyriform, L/B ratio greater than 1.6, nondeciduous in water. They were homothallic. Oogonium diameters were 26.0-47.5μm. Antheridia were mostly paragynous, amphigynous occasionally, unicellular, cylindrical. Refer to the main Phytophthora classification keys, the isolates were identified as Phytophthora sojae. Pathogenicity of all isolates was pathogenic to Hefeng-35 soybean, the inoculated soybean plants showed the same symptom as naturally infected soybean plants did. Based on the results above, the isolates were confirmed as Phytophthora sojae according to Koch's rules.The soybean plants of 14 soybean varieties with different resistance genes were then inoculated with the 47 strains of Phytophthora sojae by using hypocotyls inoculation method, respectively. The experimental results showed that 47 strains belong to 21 different pathotypes. The main pathogenic types are 3a,3c,5,7, 1a,1b,1d,4,7 and 1a,1d,4,5. Twenty-two of these stains can overcome four resistance genes, and the frequency was 46.81%. And two of them can overcomelO resistance genes, which are the highly pathogenic strains in the main producing areas in Anhui Province. The strains that can overcome Rps7 are the most, totally to 37, with frequency as 78.72%. Then the frequency of strains that can overcome Rps5, Rps1d and Rps3c was more than 50%, and their value in breeding was greatly reduced. The strains that can overcome Rps1c are the least ones, with a frequency of 6.38%. And the frequency of strains to overcome Rps1k, Rps2, and Rps6 strain was below 20%. Total of the strains with Avr-1c are 44, the frequency was up to 93.62%. And the frequency of strains with Avr-1k, Avr-2, Avr-6 was more than 80%, both this two types have high value when breeding.