Resistance level and mechanism of Penicillium digitatum to imazalil and carbendazim in Quzhou,Zhejiang

The resistance and their molecular mechanisms of 70 isolates of Penicillium digitatum from 12 citrus store houses in Quzhou city (included Kecheng and Qujiang districts,as well as Kaihua County) to imazalil and carbendazim were studied.The results demonstrated that the frequency of imazalil-resistant isolates μg/mL in Kecheng and Qujiang districts were 77.1% and 62.5%,respectively.The mean EC50 values of imazalil-resistant isolates from Kecheng and Qujiang distracts were 2.07±1.04 μg/mL and 2.35±0.73 μg/mL,respectively,which were 41.4 and 47 times higher than those of imazalil-sensitive isolates (MIC≤0.1 μg/mL).However,no imazalil-resistant isolates was detected in Kaihua,and the mean EC50 values of P.digitatum was 0.04±0.02 μg/mL.The frequencies of carbendazim-resistant isolates (MIC＞10 μg/mL) in Kecheng and Qujiang were 54.3% and 54.2%,whereas 9.1% in Kaihua.These results indicated that the frequencies of imazalil and carbendazim resistance of P.digitatum were much higher in main citrus producing areas (Kecheng and Qujiang districts) than that in non-main citrus producing areas (Kaihua),inferring that the formation of resistant population is associated with the history of fungicide application.Further study showed that the resistance mechanism of P.digitatum from Quzhou was belonged to IMZ-R3,an unique insertion sequence in the promoter region of CYP51B gene,whereas a point mutation at aa200 of β-tubulin gene from phenylalanine (F) to tyrosine (Y),which resulted from the mutation at 992 nt from T to A,was responsible for carbendazim resistance.