| Fusarium asiaticum is the main pathogen resulted in the FHB,which occurs at the JAC and Southwest wheat area in China.Phenamacril is one of the most effective new fungicides for the replacement of carbendazim in wheat.Early results of the study in the laboratory shows that mutations in myosin-5 confers resistance to phenamacril in F.asiaticum.In this paper,we studied the genotype of mutations,mutation frequency of phenamacril and the effect on the key traits of pathogen’s environmental fitness.It is very important to evaluate the risk of resistance to phenamacril,to develop drug resistance molecular detection technology and resistance control strategy.The wild susceptible strain 2021 was incubated on the subchromic concentration medium containing phenamacril for 14 days,and 239 resistant mutants were obtained from 1000 inoculated colonies,with a mutation frequency of 23.9%.The resistance to phenamacril of the mutant can inherit without drug selection.According to the distribution characteristics of the resistance level of the mutant,the resistance to phenamacril can be divided into three types:low resistance,medium resistance and high resistance.Among the 239 mutants,the ratios of low resistance,middle resistance and high resistance were 25.6%,7.3%and 67.1%,respectively,and the frequencies of high and low resistance exceeded 1/3 and 1/4.Fusarium asiaticum produced a high frequency and high resistance to phenamacril in vitro,revealing the risk of rapid resistance to it when applied in the field.The gene sequence of myosin 5 was determined for the 82 strains,and the mutant had a base change at different positions of myosin 5 compared with wild strain 2021.Among them,A135T,V151M,P204S,I434M,A577T,R580G/H and 1581F are belong to low resistance level;S418R,1424R and A577G are belong to medium resistance level;K216R/E,S217P/L and E420K/G/D are belong to high resistance level.There are 13 mutations at different protain codon and a total of 18 mutaions at different amino acid of the myosin-5.The frequency of mutation at 217 and 420 amino acid residues was the highest.We choosed represented mutations of HR,MR and SR respectively to study the difference on mycelial growth,asexual reproduction,and pathogenicity with the wile strain.The results showed that the pathogenicity of the resistant mutant did not change significantly,and the asexual reproductive ability was decreased,which could affect the competitive ability of the resistant strain in the field.Compared the mycelium growth,temperature sensitivity,asexuality and sexual reproduction,virulence and DON toxin biosynthesis between the wild strain and the wild strain whose myosin-5 was replaced by the different mutation,we foucd the growth rate and pathogenicity of each single-point mutant was not significantly different from that of wild strain;the growth rate of each single point mutant decreased with the lower of temperature and at 15 ℃ significantly;asexual,sexual reproductive capacity and pathogenicity of the single-point mutant is decreased than the wild strain;The effect on DON toxin is different with the Genotypes of mutations,however,for the codon of 217 and 420 the content of toxins is decreased than wild strain.Based on the analysis of the resistance frequency,the level of resistance,the characteristics of disease cycling and the key traits of environmental fitness,we can concluded the risk of resistance to phenamacril was mid-high grade. |
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