Resistance Risk Assessment For Fludioxonil In Bipolaris Maydis

Bipolaris maydis(anamorph:Cochliobolus heterostrophus)is a causal agent of Southern Corn Leaf Blight(SCLB),leading to annually huge loss worldwide.This disease is already on corn,sorghum,barley and wheat and caused varying degrees of reduce yields.The control of SCLB are mainly composed of chemical control,however,it is easy to produce on the fungicide resistance because the production of common fungicides types are no variety and use too many times.As a result,it leads to control drop effect and serious damage.Although fludioxonil,a phenylpyrrole fungicide with a broad spectrum of activity,is introduced in 1990s,no baseline sensitivity is established for B.maydis.And it is regarded as excellent control effect of fruits and vegetables caused Botrytis cinerea.Fludioxonil is mainly used seed treatment,soil treatment and spray method,for disease control and prevention.In recent years,it is found that Botrytis cinerea resistant to fludioxonil in the field.The molecular mechanism is that III histidine kinase HAMP repetitive structure within the domain and HATPase c had mutations.In our country,lack fungicide of prevention and control of SCLB.The purpose of this paper is to research the resistance risk assessment for fludioxonil in Bipolaris maydis and as the theoretical basis for this disease control and prevention science.The research results are as follows:(1)A total of 100 field isolates were examined to assess the resistance risk of B.maydis against fludioxonil.The results showed that the baseline sensitivity was distributed as a unimodal curve with a mean EC50 value of 0.044 ± 0.022 μg mL-1 and EC50 range of variation is 0.013～0.16 μg mL-1.(2)Evaluation results show that the resistance risk assessment for fludioxonil in Bipolaris maydis is medium.With repeated exposure to fludioxonil,all the five fludioxonil-resistant mutants(RF>100)were obtained in the laboratory.Compared with the parental isolates,the five fludioxonil-resistant mutants showed decreased fitness in sporulation and virulence.And they exhibited different features of sensitivity to various stresses:(i)the sensitivity of mutants to oxidation and osmotic pressure significantly higher than the sensitive strains;(ⅱ)the sensitivity of mutants to wall inhibitor significantly higher than the sensitive strains;(ⅲ)the mutants showed different sensitivity to cell membrane.The five fludioxonil-resistant mutants showed a positive cross-resistance between fludioxonil and dicarboximide fungicide procymidone,but not between fludioxonil and boscalid or fluazinam.All the mutants exhibited stable resistance to fludioxonil,as indicated by resistance factor values that ranged from 116.82 to 445.59.When treated with 1.0 M NaCl,all the fludioxonil-resistant mutants showed more mycelial glycerol contents than the corresponding parental isolates.Sequencing alignment results of the Bmosl indicated that the mutant R27-5 had a single point mutation(Z1125K),while the mutant R104 had a 34-bp deletion fragment between the codons of 1125th and 1236th and codes a putative attenuated 1133-AA protein.The 34-bp deletion fragment led to not only a 11-AA deletion(DNAVNQKLAVR),but also the resulting frameshift mutation and early stop.All the mutations were located in Rec domain of the Bmosl in the resistant mutants.No mutations at the Bmosl were detected in the other three resistant mutants R27-1,R27-2 and R32.Then,we presume the resistance risk assessment for fludioxonil in Bipolaris maydis may be other molecular mechanisms.