Studies On Resistance Of Fusarium Graminearum To Carbendazim

The monitor method of Fusarzum graminearum to carbendazim fungicide has been discussed in this paper. The result of the comparison of several methods, including measuring the rate of increment of colony diameter, the germination of conidia and ascospores, indicated that testing spores directly from infected ears could be used in lardge scale or primary monitoring. The rate of colony diameter increasing could be used to evaluate the resistance degree. The occurring frequency of resistant ascospores in field can be used to forecasting the development of resistance population of Fusarium gram inearum. 6062 isolates of Fusarium graminearum were monitored from some regions of Jiangsu, Zhejiang, Hubei and Shanghai from 1997 to 2000. The resultes showed that the resistance to carbendazim (MBC) fungicide had occurred in the field. In 1999,193 of 754 isolates were resistant isolates (with the resistant proportion of 31 .57%) in Haining of Zhejiang province,. It showed that resistance was very serious. Resistance degree among resistant isolates was similar. EC50 and MIC values of MBC to resistant isolates were 9.23 8 jl g/rnl and more than 100 i.i g/mI, while to isolates of wild-type were 0.584 ii glml and less than 1.4 t-?gIml respectively. The resistant isolates showed positive cross-resistance to benomyl, thiabendazole, thiophanate-methyl, but no negative cross-resistance to MDPC. The resistance of F graminearum to carbendazim could be stably herited through asexual and sexual cycles. The rate of mycelial linear growth, sporulation, pathogenicity and competition capacity of the resistant isolates were almost the same as those of the sensitive isolates. MBC resistant strains of F graminearum were obtained with a frequency Of 1/106 to 1/10?by UV irradiated conidia. All mutants showed positive cross-resistance to benomyl, thiabendazole and thiophanate-methyl. resistant phenotypes of all mutants were the same and stable in the absence of fungicide. Growth and sporulation of the resistance isolates were the same as the parent. MBC resistant and sensitive isolates of F graminearum were very sensitive to tebuconazole, dinoconazole and prochloraz with EC50 less than 0.5 i.t gIml in vitro, while thiram and chorothalonil appeared less sensitive to MBC sensitive or resistant isolates. There was no cross resistance among these fungicides. Based on experiments in vitro and in vivo, prochloraz and tebuconazole had the better effects on combating MBC resistant isolates.