Monitoring The Resistance Of Wheat Powdery Mildew To Triadimefon In Sichuan And Preliminary Study On Its Mechanism

Wheat powdery mildew is one of the most important diseases in China, due to the long-term use of the single agentia,the resistance evolved grandually.26 isolates of wheat powdery mildew (Blumeria graminis f. sp.tritici) were collected from 12 regions of Sichuan province in 2008 and 65 isolates of wheat powdery mildew(Blumeria graminis f. sp. tritici) were collected from 11 regions of Sichuan province in 2009. The resistance of these isolates to triadimefon was tested by detached leaf segment method.The results showed that the average EC5o of isolates tested in 2008 was 83.84 mg/L, and the mean resistant factor was 43.68.3.85% isolates were low resistance,46.15% isolates were moderate resistance,50% isolates were high resistance. The average EC50 of isolates tested in 2009 was 87.62 mg/L, which 95.38% strains already have resistance to agentia, the mean resistant factor was 41.92.4.61% strains were sensitive to agentia.6.15% isolates were low resistance, 36.92% isolates were moderate resistance,52.3% isolates were high resistance. The results may provide a reference for management of triazole fungicide resistance of wheat powdery mildew, as well as the development and use of triazole fungicides in china. In order to control and delay the resistance, we need to explore the mechanism of the resistance.The mechanism of triazole fungicide is to restrain the activity of sterol 14-a-demethylase P450 (which was called P450 for short and CYP51 in fungi). which can cause structure and function damage of cell membrane and eventually result in death of cell. At present we think the reason for the resistance to triazole is point mutation in the CYP51 gene, the affinity between enzyme and agentia decreased, resulting in the rise of resistance. The experiment is inducing variation by agentia, first inducing the low resistant into higher resistance, then inducing the higher resistance into very high resistance. By sequece comparison of the low, higher, very high strains in CYP51 gene, we find the mutation of nuclear base at the position of 234 and 458 result in the change of amino acid at the position of 79 and 136, respectively. The Tyr at the position of 136 has changed to Phe in the amino acid encoded by the the higher resistance isolates CPY51. Not noly the Tyr at the position of 136 has changed to Phe, but also the Thr at the position of 79 has changed to Ser in the amino acid encoded by the the very high resistance isolates CPY51. It followed that,the mutation at position 458 in the DNA sequece of CPY51 controled the higher resistance. Thus the mutation at position 234 controled the very high resistance. The results can provide a reference for developing new mechanism of fungicide and further researching mechanism of resistance of wheat powdery mildew to triadimefon.