| As a worldwide plant pathogenic fungus,Sclerotinia sclerotiorum(Lib.)de Bary is one of the plant pathogenic fungi that are most difficult to control and this pathogen is extremely harmful to agricultural production of rapeseed,peanut,sunflower,etc.At present,the control of this pathogen mainly relies on chemical agents such as carbendazim and dimethachlone.This project investigated the preconditioning effect of dimethachlone on the mycelial growth and virulence of S.sclerotiorum and explored the mechanism of dimethachlone preconditioning on pathogenicity stimulation.The main results are as follows:S.sclerotiorum was cultured on potato dextrose agar(PDA)medium containing different concentrations of dimethachlone as the preconditioning treatment.Low doses of dimethachlone can stimulate the mycelial growth of S.sclerotiorum.Preconditioning dimethachlone at 0.00005 to 0.005 μg/m L had stimulatory effects on mycelial growth of three sensitive isolates and the average maximum stimulation amplitude was 10.96 ± 0.27%(SD),and dimethachlone at 0.1 to 20 μg/m L had stimulatory effects on mycelial growth of three dimethachlone-resistant isolates and the average maximum stimulation amplitude was12.14 ± 1.17%(SD).After the growth-stimulated preconditioned mycelia were transferred onto PDA without fungicide,the average maximum stimulation amplitude of the mycelial growth for the six isolates was 10.48 ± 0.86%(SD)compared with the un-preconditioned control.After the growth-stimulated preconditioned mycelia were transferred on rapeseed leaves without fungicide,the average maximum stimulation amplitude of pathogenicity for the six isolates was 16.30 ± 2.19%(SD)compared with the un-preconditioned control.After the preconditioned mycelia were transferred onto PDA containing high doses of dimethachlone,the maximum stimulation amplitudes of mycelial growth of sensitive isolates HLJMG1 W,GS1W and GS2 W were 10.51%,12.40%,and 9.67%,respectively,compared with the un-preconditioned control.The maximum stimulation amplitudes of mycelial growth of dimethachlone-resistant isolates HLJ4 W,HLJ5W,and HLJ6 W were12.01%,17.52%,and 9.91%,respectively.After the preconditioned mycelia were transferred on rapeseed leaves sprayed with high doses of dimethachlone,the maximum stimulation amplitudes of pathogenicity of sensitive isolates HLJMG1 W,GS1W,and GS2 W were 20.95%,20.05%,and 22.04%,respectively,compared with the unpreconditioned control.The maximum pathogenicity stimulation amplitudes of dimethachlone-resistant isolates HLJ4 W,HLJ5W,and HLJ6 W were 15.14%,16.40%,and17.66%,respectively.After the preconditioned mycelia were transferred onto PDA containing high doses of iprodione,the maximum stimulation amplitudes of mycelial growth of isolates HLJ4 W,HLJ5W,and HLJ6 W were 10.83%,10.00%,10.32%,and 10.55%,respectively,compared with the un-preconditioned control.But after the preconditioned mycelia were transferred onto PDA containing high doses of carbendazim and boscalid,there was no significant difference in mycelial growth compared with the un-preconditioned control(P > 0.05).After the preconditioned mycelia were transferred on rapeseed leaves sprayed with high doses of iprodione,the maximum pathogenicity stimulation amplitudes of isolates HLJ4 W,HLJ5W and HLJ6 W were 10.83%,10.00%,10.32%,and 10.55%,respectively,compared with the un-preconditioned control.But after the preconditioned mycelia were transferred on rapeseed leaves sprayed with high doses of carbendazim and boscalid,there was no significant difference in pathogenicity compared with un-preconditioned the control(P >0.05).Low doses of dimethachlone preconditioning can reduce the control efficacy of dimethachlone against S.sclerotiorum.After preconditioned mycelia of isolate HLJMG1 W was transferred on rapeseed leaves sprayed with 20 and 40 μg/m L dimethachlone,the protective efficacy against S.sclerotiorum decreased from 63.36% and 79.30% to 55.03%(P = 0.039)and 70.79%(P = 0.046),respectively,and the curative efficacy decreased from51.80% and 67.68% to 41.13%(P = 0.026)and 57.80%(P = 0.045),respectively,compared with the un-preconditioned control.Low doses of dimethachlone preconditioning also reduced the protective efficacy of iprodione on rapeseed leaves against S.sclerotiorum,but the protective efficacy of carbendazim and boscalid has no significant difference compared with the un-preconditioned control(P > 0.05).The study on the stimulation mechanisms showed that dimethachlone preconditioning had no significant effect on the activities of NADPH oxidase(P = 0.6),cutinase(P = 0.75),or xylanase(P = 0.93)of S.sclerotiorum.Dimethachlone preconditioning had no significant effect on the expression of NADPH oxidase genes Ss NOX1 and Ss NOX2,xylanase gene Ss XYL1,γ-glutamyl transpeptidase gene Ss Ggt1 or forkhead box(FOX)transcription factor Ss Fkh1 of S.sclerotiorum(P > 0.05).In summary,low doses of dimethachlone preconditioning can stimulate the mycelial growth of S.sclerotiorum on PDA without fungicide or containing high doses of dimethachlone and iprodione.Low doses of dimethachlone preconditioning can stimulate the pathogenicity of S.sclerotiorum on rapeseed leaves without fungicide or sprayed with high doses of dimethachlone and iprodione.And low doses of dimethachlone preconditioning can reduce the control efficacy of dimethachlone and iprodione against S.sclerotiorum.These studies are of great significance for an in-depth understanding of the characteristics and mechanisms of the stimulatory effect of fungicides preconditioning on phytopathogens and will play an important guiding role in the scientific and rational application of dimethachlone to control S.sclerotiorum. |
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