Stimulatory Effects Of Low Doses Of Dimethachlone On Sclerotinia Sclerotiorum

The ascomycete fungus Sclerotinia sclerotiorum(Lib.)de Bary is a devastating necrotrophic plant pathogen with an unusually broad host range and worldwide distribution.The objective of this study was to investigate the effects of low-dose dimethachlone on the growth and pathogenicity of dimethachlone-resistant strains,and the biochemical and molecular mechanisms underlying the stimulatory phenomenon.Low doses of dimethachlone significantly stimulated the growth of dimethachlone resistant strains.Dimethachlone in potato dextrose agar(PDA)at concentrations from 0.1 mg/L to 50 mg/L significantly promoted the mycelial growth of the strain JMS14-J1,and the percent of maximum growth stimulation was 165.67%.Dimethachlone at concentrations from 0.1 mg/L to 1.6 mg/L promoted the growth of the strain HLJ3,with a maximum percentage of 56.18%.Dimethachlone at concentrations from 1 mg/L to 40 mg/L significantly promoted the growth of the strain HLJ4,and the percent of maximum growth stimulation was 25.46%.In addition,dimethachlone increased the number and dry weight of sclerotia of JMS14-J1 strain.Low doses of dimethachlone significantly increased pathogenicity of resistant strains.Dimethachlone sprayed on rapeseed leaves at concentrations from 10 mg/L to 400 mg/L increased pathogenicity of JMS14-J1 and the percent of maximum stimulation was 86.84%.Dimethachlone at concentrations from 0.01 mg/L to 4 mg/L increased pathogenicity of HLJ3,and the percent of maximum stimulation was 31.80%.Dimethachlone at concentrations from 0.1 mg/L to 1mg/L increased pathogenicity of HLJ4,and the percent of maximum stimulation was 70.25%.Pretreatment with 50 and 100 mg/L dimethachlone in PDA significantly promoted the mycelial growth of the hyphae that was transferred to no-toxic PDA(first generation)and had no significant effects on the growth of the second generation hyphae.Pathogenicity was significantly increased for mycelia pretreated with dimethachlone at concentration from 1 mg/L to 100 mg/L and the percent stimulation ranged from 36.69% to 123.74%.The activities of catalase,peroxidase,superoxide dismutase enzymes and the secretion of H+ did not increase significantly after exposure to low doses of dimethachlone.Scanning electron microscope showed that hyphae treated with dimethachlone at 10 mg/L were thinner and less branched than that of the non-treated control.Dimethachlone at 10 and 50 mg/L facilitated the formation of mycelial biomass on rapeseed leaves.The result of RNA sequencing showed that dimethachlone at 10 mg/L had significant effects on the levels of gene expression.A total of 1018 genes were up-regulated and 1338 genes were down-regulated.The results of qRT-PCR correlated well with the results of RNA sequencing.These results laid the foundation for future studies on the major genes for the hermetic effects of dimetachlone on S.sclerotiorum.