Resistance-Risk Assessment Of Phytophthora Capsici To LH-2010A

Pepper Phytophthora blight caused by Phytophthora capsici is a devastating disease which can bring huge losses of pepper.The chemical control is still a main method of control of the disease in the production so far.LH-2010A is a novel formamide fungicide that synthesized in China. It has good inhibitory effect to Phytophthora capsici. In order to investigate the sensitivity and resistance-risk of Phytophthora capsici to LH-2010A,this study was undertaken on detection of sensitivity to LH-2010A,the resistant mutants reducing, cross-resistance of LH-2010A resistant mutants to other fungicides with different mechanisms and the biological characteristics between the sensitive and resistant mutants. The main results are as follows:1.Fourty-two isolates of P. capsici collected from four regions in Shandong,Beijing,Zhejiang, Yunnan were tested by measuring mycelial growth rate in order to explicit the sensitivity of P. capsici to LH-2010A.The results showed that the42isolates were all sensitive to LH-2010A, there was small difference in strains collected in different regions with a mean EC50of2.214±0.403mg-L-1. The sensitivity frequency of P. capsici to LH-2010A distributed as a unimodel curve,which showed there were no resistant subpopulation among these isolates,so this sensitive baseline was suitable for resistance monitoring of P. capsici to LH-2010A.2.The four LH-2010A-resistant mutants were selected by UV-irradiating and fungicide-selection,its resistance level is between57.8～237.4times.After10th fungicides-free medium,the resistant levels of four resistant mutants were stable. It measured the sensitivity of LH-2010A-resistant mutants to other7fungicides,mutants exhibited positive cross resistance to fluopicolide,metalaxyl and cymoxanil,while negligible cross resistance to dimethomorph, chlorothalonil, mancozeb, propineb.Therefore, it can be used mixed with dimethomorph or protective fungicides or rotating, which can delay resistance to pathogens.3.There was a different degree of difference in virulence,sporulation and the growth rates and dry-weights between resistant strains and TA.The growth rates and dry-weights of mycelium of four resistant mutants were lower than that of the sensitive,especially the resistant by UV-irratiating.The sensitive and resistant all caused the pathogenesis of leaves,the TA-UV1 was higher than TA in virulence and sporulation,while the TA-R had a similar level and TA-UV2、TA-UV3were lower than TA in virulence,sporulation.It indicated that it has a difference among the resistant mutants.4.To explore the physiological fitness beween the sensitve and resistant isolates,the mycelial growth was meaured in different carbon and nitrogen sources, pH and temperatures,under the conditions of different carbon sources, the sensitive strain growed best in sucrose and soluble starch, while the resistant strains growed best in maltose and glycerol; under different nitrogen conditions, all isolates growed well in potassium nitrate and sodium nitrate better. Their optimum pH and temperature were both7and26℃.It showed that their response to pH and temperature difference was not obvious.