Study On The Inhibitory Mechanism Of The Mixture Of Boscalid And Prochloraz On The Growth And Pathogenicity Of Sclerotinia Sclerotiorum

Sunflower Sclerotinia Rot caused by Sclerotinia sclerotiorum is the most serious disease to the sunflower industry.At present,chemical control becomes a key approach to this disease.However,The resistance caused by using some of registered fungicides on S.sclerotiorum for long time has developed more and more serious.Compounding of fungicides with different mechanisms is one of the main strategies to effectively delay the emergence of fungicides resistance to S.sclerotiorum.In this study,two fungicides with different mechanism were compounded to explore the efficiency mechanism of boscalid and prochloraz act on S.sclerotiorum.This will provide a scientific basis for revealing the synergistic fungicides in development and application.The main results are as follows:1.In vitro conditions,the combined virulence of the mixture of boscalid and prochloraz to S.sclerotiorum was determined.The results showed that boscalid mixed prochloraz has better inhibitory effects on S.sclerotiorum in different ratios,and when boscalid mixed prochloraz with the ratio of 1:1,the synergistic inhibition was the strongest,and the EC₅₀values of 0.0367 and0.0246μg/m L for mycelium and spores,respectively.The inhibitory effect of the mixture of boscalid and prochloraz on the growth of S.sclerotiorum increased with the increase of the concentration,and it could effectively inhibit the growth of S.sclerotiorum mycelium and sclerotium,the germination rate of sclerotium and the formation rate of ascomycetes,and the inhibitory effect was significantly better than boscalid or prochloraz.2.It was detected by SEM and TEM observation of mycelial morphology and ultrastructure that the S.sclerotiorum hyphal morphology was severely damaged by the mixture of boscalid and prochloraz,accompanied with tumor-shaped protrusions,and destroyed S.sclerotiorum cell structure,resulting in plasmolysis,dissolution of most organelles,and severe cell vacuolization.3.In vitro conditions,Changes in the cell membrane system,substance metabolism and pathogenic factors of S.sclerotiorum were determined after treatment with EC₅₀and EC₉₅concentrations of different agents.The results showed that the cell membrane of S.sclerotiorum was severely disrupted,the cell membrane permeability and the conductivity increased under the treatment of different agents,which also decreased inclusions content in mycelium.The oxalic acid excreted by S.sclerotiorum and its activity of cell wall degrading enzymes were significantly reduced by treated with the mixture of boscalid and prochloraz.Compared with controls,the expression of the three pathogenic genes Ss-oah1,Ss-pg1 and Ss-pg3 of S.sclerotiorum were respectively reduced 69.90%,55.00%and 71.30%.The effects of the mixture of boscalid and prochloraz on cell membrane permeability,substance metabolism,major pathogenic factors and related genes of S.sclerotiorum were significantly effect than those of the two single agents.This indicated that the mixture of boscalid and prochloraz could disrupting the cell membrane system,down-regulating the secretion of oxalic acid and the activity of cell wall degrading enzymes to decrease the virulence of S.sclerotiorum.4.Field experiments showed that the mixture of boscalid and prochloraz has higher control effects than that of boscalid,prochloraz and iprodione·fluazinam after 7 and 14 days of the last application.Among them,the best control effects were achieved when the ratio of the mixture of boscalid and prochloraz was 1:1,and it was 60.03%and 65.33%respectively.The yields of the mixture of boscalid and prochloraz with 1:1 had increased to 65.07%and 28.50%compared with the blank control and iprodione·fluazinam respectively,It indicated that the mixture of boscalid and prochloraz has a synergistic effect.