| Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum Schwade, is one of the most economically important diseases worldwide and controlling object on wheat prodution at home and abroad. FHB not only causes reduction in grain yield and quality, and also produces fungi mycotoxin by the main deoxynivalenol, which are larger harmful to animals and people. At present, chemical control is still a main control measures for management of FHB in the production, but the long-term use of a single class of fungicides may result in resistant occurrence of resistant strains to fungicides and low control efficacy. Tebuconazole is high activity, broad-spectrum, low toxicity and strong systemic DMIs fungicides, which has specific mode of action to F. graminearum, and has not been used at large scale in China. Therefore, this study was undertaken on the sensitivity baseline to tebuconazole in F. graminearum and cross-resistance relationship between tebuconazole and the other fungicides with different active mechanisms in F. graminearum, risk assessment of resistance to tebuconazole in vitro, the mechanism of the physiological mechanism of resistance to tebuconazole. The main results are as follows:1. The baseline sensitivity of F. graminearum to tebuconazole was established. During 2009 to 2010, the sensitivity to tebuconazole of 120 isolates of F. graminearum had been collected from different provinces including HeNan, Shangdong and Hebei, was tested by mycelial growth inhibition method. The results demonstrated that the EC50 values of the compound inhibiting growth of F. graminearum was ranged from 0.0072μg/mL to 0.2007μg/mL, the difference between maximum and minimum are 27.88 times. With the mean value of 0.1026±0.0454μg/mL, MIC>0.8μg/mL. The sensitivity frequency of 120 wild isolates of F. graminearum to tebuconazole distributed as a single peak cure, so these isolates were seen as wild isolates. The date could be used as baseline sensitivity of resistance monitoring of tebuconazole to F. graminearum in field.2. Sensitivity of eleven relatively sensitive isolates to tebuconazole, iprodione, thiram, chlorothalonil, difenoconazole and carbendazim were determined by mycelial growth inhibition method to make sure that it existed cross resistance or not between tebuconazole and other diverse active mechanism fungicides. The results showed that tebuconazole and carbendazim inhibited strongly mycelia growth of F. graminearum. The linear regression showed that there were no positively-correlated cross resistance between tebuconazole and other diverse active mechanism fungicides.3. In laboratory, total nine resistant mutants to tebuconazole derived from wild-type isolates had been obtained through ultra-violet (UV) irradiating at the dosage of EC90 or fungicide training methods. The resistant levels ranged from 34.26 to 186.03 times. Mutation frequencies were separately 1.11 % and 0.91%. According to the FAO standard, these resistant mutants could be divided into three resistance phenotypes of low level resistance (LR), moderate level resistance (MR) and high level resistance (HR), of which determined by the EC50 values 2.0～20.0μg/mL(LR), 20.1～100.0μg/mL(MR) and more than 100.0μg/mL(HR). After resistant mutants to tebuconazole were cultured in the PDA medium without fungicide for 17 generations, five resistant isoslates still kept high resistant level. Some biological characteristics of resistant mutants were studied in laboratory, the results showed that resistant mutants exhibited not diversity in mycelial growth rate, mycelium dry weight, pathogenicity and fitness with their parantal isolates. Based on the above, it was suggested that F. graminearum had a moderate or high resistance risk to tebuconazole. Therefore, we could conclud that resistant mutants could be emerged quickly once tebuconazole was often used, and it was suggested that tebuconazole should be used alternately with other different active mechanism fungicides without cross-resistance to avoid or delay the development of resistance.4. Comparison resistance mechanism of F. graminearum isolates with parental and resistant to tebuconazole, determined on physiological were done. The results indicated that resistant mutants and parental isolates for mycelial gowth capacity were more affected in the KC1 and glucose concentrations. At different concentrations, all isolates show significant osmotic pressure difference. It can be drawn KCl and glucose on capsici does have to provide nutritional and osmotic inhibition. Although tebuconazole in high concentrations resistant isolates in vivo electrolyte to leak out more, with the treated time and concentration increase, the resistant strains inclusions more leakage. So these reasons may be resistant mechanism to tebuconazole.5. The highest synergistic ratio of mixtures was found to be 1: 11, which in the 11 mixtures of tebuconazole with chlorothalonil through test of the synergistic interaction of the mixtures of tebuconazole with chlorothalonil against mycelial growth of F. graminearum using different ratio and ingredient. SR value was 84.38. 1: 11 can filtrate appropriate mixtures to reduce the resistance risk of F. graminearum to tebuconazole by alternating with tebuconazole in field. |
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