Baseline Sensitivity Of Stemphylium Solani To Fluxapyroxad And Resistance Risk Assessment Of Stemphylium Solani

Tomato gray leaf spot disease is a new fungal disease that has occurred and prevalent in China in recent years.Due to the lack of tomato varieties resistant to gray leaf spot in China and planting in protected areas,gray leaf spot disease of tomatoes is prevalent throughout the country,causing serious losses to tomato production.Therefore,screening effective fungicides for tomato gray leaf spot is an important demand in production.In this paper,the sensitivity baseline of phytophthora infestans to fluxapyroxad and fludioxonil was established.Resistance risk assessment of the fluxapyroxad was carried out.The bioactivities of fluzoxamide against Stemphylium solani,botrytis cinerea,Alternaria solani,Fulria fulva and Fusarium oxysporum with EC50 values of 0.0967,0.2109,0.2926,11.9097 and 24.9849 ?g/mL respectively.The baseline sensitivity and resistance risk of Tomato Gray Leaf Spot to fluzoxamide were studied by using strains isolated and preserved from tomato diseased leaves in Shouguang greenhouse in Shandong Province in 2008.The sensitivity baseline of 100 strains of Stemphylium solani was established by mycelial growth rate method.The results showed that the EC50 value of Stemphylium solani was ranged from 0.0154 to 0.2284?g/mL with 95%confidence interval was ranged from 0.074?0.107 ?g/mL.The frequency distribution of sensitivities was representing a curve of single peak.The average EC50 values against fluxapyroxad were 0.093±0.070 ?g/mL for mycelial growth.Six fluxapyroxad-resistant mutants were obtained by growing sensitivity strains on potato sucrose agar.Mutation frequency was 6%.Range of resistance factor were 184.04?112.56?103.43?57.74?178.16 and 229.12 respectedly.The mycelial growth of the fluxapyroxad resistant strain was basically the same as that of the parent strain,and the pathogenicity was slightly reduced,and it has high suitability.The results of cross-resistance showed that there was no cross-resistance between fluxapyroxad and fludioxonil,iprodione,azoxystrobin and fluazinam,and it had positive cross-resistance with the boscalid and pydiflumetofen.Conidia of three parent strains and four other susceptible strains were treated with fluxapyroxad(0,0.625,1.25,2.5,5,10 ug/mL)and conidia of six fluxapyroxad-resistant mutants were treated with fluxapyroxad(0,3.25,6.5,12.5,25,50 ug/mL).The EC50 value of spore germination inhibition rate of susceptible mutants was ranged from 1.772?4.157?g/mL.The EC50 value of spore germination inhibition rate of fluxapyroxad-resistant mutants was ranged from 14.992?30.458 ?g/mL.The baseline sensitivity of Stemphylium solani to fludioxonil was determined using 100 strains.The results showed that the EC50 values of Stemphylium solani was ranged from 0.0294?0.1373 ?g/mL with the mean EC50 value of 0.062±0.061 ?g/mL and 95%confidence interval was ranged from 0.058?0.065 ?g/mL.The synergistic effects of fluxapyroxad with fludioxonil on the growth inhibition of tomato gray leaf spot were determined by mycelial growth rate method with 10:3,7:3,5:3,1:1,3:5,3:7 and 3:10 compositions,respectively.The results showed that the fluxapyroxad with fludioxonil was synergistically matched with the mycelial growth of Stemphylium solani by 10:3,7:3,5:3,1:1,3:7 ratio,to 3:5,3:10 ratio compounding revealed additive biological response,no antagonistic effect.Fluxapyroxad,fludioxonil and mixtures of fluxapyroxad and fludioxonil(1:1)had protective effects on tomato leaves in vitro.Moreover,the control effect of compound agent is higher than that of single agent.43 isolates of S.solani were collected from greenhouses in shouguang,Shandong Province.Twenty-nine resistance mutants to fluzoxamide were detected on drug-containing PSA medium,accounting for 67.44%of the tested strains.