Sensitivity Of Blumeria Gram In Is F. Sp. Tritici Isolates To Triadimefon And Its Relationships With Pathogen Virulence And Genetic Diversity

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is common in China. Yield loss caused by this disease often reaches hundreds of millions kilograms or even more annually. Now the resistance of B. graminis f. sp. tritici to triadimefon is very serious. In this study, the sensitivities of B. graminis f. sp. tritici to triadimefon and fenpropidin was detected, and relationship of cross resistance in B. graminis f. sp. tritici between triadimefon and fenpropidin was also analysed. Furthermore, the fungicide resistant mutation sites at136and398in CYP51gene related with resistance of B. graminis f. sp. tritici isolates to triadimefon were detected. The relationships of sensitivity to triadimefon, virulence diversity and genetic diversity were analysed. The results can be used to reveal the influence of fungicides application on pathogen virulence and genetic diversity, and to provide theoretical basis for disease control strategy.The sensitivity of100isolates of B. graminis f. sp. tritici to triadimefon and fenpropidin sampled from eight provinces or cities was tested by seed treatment and detached leaf segment methods. The results showed that the mean EC50of all the tested isolates to triadimefon was72.97mg/L, and the mean resistance factor (RF) was34.92. The frequency of resistant isolates to triadimefon reached97.00%. The resistance factor of the tested isolates from Shandong to triadimefon was the highest, reached52.63. The base-line of sensitivity of B. graminis f. sp. tritici to fenpropidin was determined, and was100.47mg/L. There was no significant cross-resistance between triadimefon and fenpropidin in B. graminis f. sp. tritici population.The resistant mutation sites at136and398in CYP51of B. graminis f. sp. tritici isolates were detected using Polymerase Chain Reaction (PCR). The results showed that the frequencies of mutation sites at136and398were70.59%and56.67%, respectively. There was no mutation in these two sites in sensitive isolates. Mutation both at136and398sites were found in27isolates with moderate and high resistance.Analysis of virulence diversity by MEGA4of68isolates from8provinces or cities showed that, virulence diversity of B. graminis f. sp. tritici isolates sampled from Shandong Province was the lowest, and its index of virulence gene diversity was0.1225. Isolates sampled from Gansu Province had the highest virulence diversity, and its index of virulence gene diversity was0.2345. Clustering analysis of virulence pahthotypes showed that isolates from Sichuan and Gansu, Yunnan, Guizhou and Henan had similar virulence structure. Isolates from Shandong Province was more different from other ones. There was no significant relationship between virulence distance and geographic distance. Analysis of genetic diversity of B. graminis f. sp. tritici isolates using AFLP method showed that the genetic diversity of isolates sampled from Henan Province was the lowest, and the index of genetic diversity was0.1591, where isolates sampled from Beijing had the highest genetic diversity. Clustering analysis of genetic distance by MEGA4showed that genetic diversity of isolates sampled from Beijing and Shandong, Gansu and Sichuan, Hubei and Henan were similar, respectively. There was significant relationship between genetic distance and geographic distance, which indicated that the genetic similarity was higher when the sites were closer.By correlation analysis among the sensitivity of B. graminis f. sp. tritici isolates to triadimefon, virulence diversity and genetic diversity, the results showed there was no significant correlation among average EC50, variation coefficient of EC50, virulence diversity and genetic diversity, however relationship between EC50values of sensitivity to triadimefon and numbers of virulence genes of68B. graminis f. sp. tritici isolates fitted a logarithmic function (r=0.2718, P=0.0341).