Resistance Risk Assessment For Fusarium Fujikuroi And F.Oxysporum F.sp. Melonis Against Phenamacril

Rice bakanae,caused by Fusarium fujikuroi,is one of the most devastating fungal diseases in rice in China.Fusarium wilt,caused by Fusarium oxysporum f.sp.melonis,is one of the most devastating fungal diseases in melon.Phenamacril is a novel fungicide with unique chemical structure,specific mode of action,good compatibility to environment,and totally independent intellectual property rights.Owing to excellent inhibitive activity against Fusarium spp,this fungicide can be used to govern populations of both carbendazim-resistance and ergosterol biosynthesis inhibitor resistance.This fungicide will be used to control diseases of rice bakanae and melon Fusarium wilt in China,but the resistance risk assessment of these two pathogens is unavailable up to date.Therefore,the research was conducted in current study and the main results present as following.(1)Fusarium fujikuroi exhibited high resistance risk against phenamacril,a cyanoacrylate fungicide.A total of 12 phenamacril-resistant mutants of Fusarium fujikuroi were domesticated with a series of increasing concentrations of phenamacri.Resistance frequency is as high as 12.9%by respectively transferring discs of mycelia on PDA plates with phenamacril-amending,and this ratio is far more than fungicides with other mechanism.All the mutants significantly reduced both mycelium growth and virulence against tomato fruits,however,significantly increased in conidation.Point mutations at myosin 5 of F.fujikuroi conferred high resistance against phenamacril.Two genotypes at the myosin 5 were found,(i)a point mutation occurred at the codon 326th[AGG(Arg)→AG(?)(Ser),(ii)point mutations occurred at the codon 326th[AGG(Arg)→AG(?)(Ser)]and the codon 435th[GTC(Val)→(?)TC(Phe)].Therefore,a high level of resistance risk of F.fujikuroi against phenamacril is recommended.During seed treatment,usage frequency and level must be considered to establish a sustainable strategy to reduce or delay the occurrence of field resistance,and extend its service life.(2)Fusarium oxysporum f.sp.melonis presented high resistance risk against phenamacril,a cyanoacrylate fungicide.A total of 18 phenamacril-resistant mutants of Fusarium oxysporum f.sp.melonis were domesticated with a series of increasing concentrations of phenamacril in current study.Resistance frequency is as high as 17.6%by successively transferring discs of mycelia on PDA plates with phenamacril,and this ratio is far more than fungicides with other mechanism.All the high resistance mutants significantly increased in mycelium radial growth,virulence against tomato fruits and conidation.A point mutations at myosin 5 of F.oxysporum f.sp.melonis was found and maybe conferred resistance against this fungicide.Therefore,a high level of resistance risk of F.oxysporum f.sp.melonis against phenamacril is recommended.During treatment with this fungicide,its usage frequency and level must be considered to establish a sustainable strategy.