Bilogical Activities And Resistance Risk Assessment Of Three Strobilurin Fungicides Againist Neopestalotiopsis Clavispora

Moyeam（Ampelopsis grossedentata）,is rich in a variety of flavonoid compounds and has antioxidant,anti-lipid,anti-bacterial and anti-inflammatory effects.In recent years,diseases related to moyeam have been found in Yongding District of Zhangjiajie,such as moyeam canker and moyeam leaf spot.These diseases have caused serious losses to the local farmers’economy,so it is necessary to carry out identification and screening of control agents for moyeam diseases.This study firstly isolated and identified the pathogen of moyeam leaf blight.And through preliminary experiments,it was found that three Qo Is,picoxystrobin,azoxystrobin and pyraclostrobine had good inhibitory effect on pathogen of moyeam leaf blight in vitro.The biological activities of three Qo Is against N.clavispora were determined,and the resistance risk of N.clavispora to picoxystrobin was evaluated.Through the investigation of moyeam disease in Yongding District,Zhangjiajie,a large number of withered leaves were found in the field,which led to the death of moyeam leaves.According to its field symptoms,the disease was named as moyeam leaf blight.We isolated and purified 19 strains with similar morphology from collected diseased leaves.Then through morphological observation,molecular biology and pathogenicity determination,the pathogen of moyeam leaf blight was identified as N.clavispora.The method of mycelial growth rate was used to establish sensitivity baselines of N.clavispora to picoxystrobin,azoxystrobin and pyraclostrobine.The result showed that the average EC₅₀ of mycelial growth of 19 strains of N.clavispora were 0.0252±0.0125μg/m L,0.0398±0.0125μg/m L,0.0026±0.0051μg/m L,respectively.The average EC₅₀ values for spore germination were 0.0048±0.0022μg/m L,0.0073±0.0034μg/m L and 0.00029±0.00027μg/m L,respectively.There was no difference in the sensitivity of N.clavispora to the three fungicides,and no resistant population was found.The effects of three fungicides on the biological activity of N.clavispora were determined.The results showed that at the concentration of 10×EC₅₀,the three fungicides could cause malformation of mycelia and decrease of apical branch of N.clavispora.At the concentration of EC₉₀,the three fungicides could increase cell membrane permeability and relative conductivity of N.clavispora.At the same time,ATP content in cells is reduced,which affects cell energy acquisition and inhibits cell respiration.Three picoxystrobin-resistant mutants were obtained by means of combining fungicide acclimation with uv,of which one strain with high,medium and low resistance.Resistance frequency was 5×10^-3.And the resistance could be inherited stably.Compared with the parent strain,the dry weight of mycelia and sporulation of resistant mutants decreased.The colony diameter of high resistant strains decreased and mycelia grew malformed,but there was no significant difference among other resistant strains.The high resistant mutants had cross-resistance to azoxystrobin and pyraclostrobine,but had no cross-resistance to difenoconazole,phenamacril and carbendazim.There was no cross-resistance between medium and low antibiotic strains.The pathogenicity of resistant mutants was lower than that of their parents.The results showed that N.clavispora had a medium risk of resistance to picoxystrobin,and it was suggested that picoxystrobin should be used alternately or in combination with other agents without cross-resistance to delay the development of picoxystrobin resistance.