Biological Properties Of Botrytis Cinerea Resistant To Boscalid In Field And Development Of Fungicides For Resistance Management

Gray mold,caused by Botrytis cinerea,is one of the main diseases in fruits and vegetables.Powerful sporulation,wide genetic variability and strong adaptability of this pathogen make it difficult to control the disease effectively,leading to decreased yield and quality of fruits and vegetables.Boscalid is a new carboxamide,attributed to succinate dehydrogenase inhibitors(SDHIs)and widely used abroad,and resistance of B.cinerea to boscalid is frequently reported.However,boscalid has not been officially registered until 2012 in China.Although this fungicide has been used to control gray mold on vegetables and fruits for 2 years in China,whether boscalid-resistant pathogen populations have formed,and which genotype of resistant populations is dominant in field are concerned.Therefore detection of resistance of B.cinerea against boscalid,biological characteristics of resistant strains,main resistance genotypes in field,and development of synergism mixtures for managing resistance subpopulations were involved in the current study.As follows were main conclusions:Boscalid-resistant subpopulation in Nanjing suburb formed after 2 years usage of the fungicide,while no resistance was detected in Shouguang,Shandong.Of 94 strains separated from diseased strawberry fruits 3 moderately-resistant strains were detected in Lishui,Nanjing,however,no resistance was ever found from 187 strains collected Shouguang,Shandong.Fitness of field boscalid-resistant isolates was significantly lower than that of wild-type isolates and the resistant genotype i.e.,H272R of SDHB subunit was dominant in field.The results showed that resistance against SDHIs was genetically stable.Compared with the sensitive isolates,hypha growth,virulence and respiratory rate of the field resistant isolates were significantly lower than that of sensitive isolates,except for sporulation.Cross resistance testes indicated that no cross resistance was found among boscalid with fluazinam,fluopyram,SYP-Z048 or fludioxonil.Sequence alignment analysis of 4 subunits of succinate dehydrogenase from both resistant and sensitive strains revealed that the substitution H272R,concordant with the previous reports,was located on SDHB subunit of the three resistance isolates.40%Fluazinam · boscalid wettable powder was developed for managing resistance populations of B.cinerea,and applied for Chinese national inventive patent The results showed that fluazinam and boscalid at the ratio 1:3 exhibited the optimal synergism(SR=1.83),while fluazinam and fluopyram at the ratio 5:1 exerted excellent synergism(SR=1.69).Field trial data showed that the two mixtures were more effective in controlling gray mold than each of the single fungicide at the same dose.40%Fluazinam-boscalid wettable powder was developed by screening suitable wetting agents,dispersants and carriers.After optimization,the formula composition was determined:10%fluazinam technical product,30%boscalid technical product,5%stabilizer(S-60),6%dispersant(N),1%wetting agent(K12),1%detergent(LS),5%white carbon black,and 41%kaolin.