Inhibitory Mechanism Of Polysiloxane-polyquaternary Ammonium Salt Block Copolymer Against Rice Sheath Blight

Rice sheath blight?Rhizoctonia solani,R.solani?,is one of the major biological constrains on rice production.Sclerotia as one of the special morphological forms in asexual reproduction of R.solani.It is rather difficult for common anti-RshB drugs to effectively prevent and completely control the disease due to the lack of stable adsorption on the sclerotial surface or penetrating inside.Therefore,based on the analysis on microstructure of sclerotial R.solani,this paper points out that the effective contact between drugs and mycelia in sclerotial inner layer or germinated from the sclerotia is the very precondition of preventing and controlling sclerotia.In addition to our previous studies,this paper utilizes the specific adsorption and permeability of a new type amphiphilic macromolecular quaternary ammonium salts?Polydimethylsiloxane-polymethacrylate block copolymers containing quaternary ammonium salts,PDMS-b-QPDMAEMA,Si_x-Q₅ series?,to anchor the functional molecules stably on the surface of sclerotia and further penetrate into the sclerotia.Therefore,the sclerotial germination can be inhibited to cut off the infection cycle,to achieve the goal of preventing the disease from the sources.The results are as follows.?1?The amphipathic macromolecular quaternary ammonium salt?QAS?copolymers?the series of Si_x-Q₅?,the hydrophilic QAS homopolymer?Poly?2-methacrylamido?propyltetrabenzyldimethylammonium chloride,PQD-BC?and commercial small-molecular QAS?benzalkonium chloride,BC?were stduied systematically in the aspect of antifungal activity against mycelial R.solani,found that the evaluation method for the antifungal activity of amphiphilic macromolecular quaternary ammonium salt was applied to the mycelial dry weight,and the growth rate method was not suitable for its evaluation.?2?The antifungal mechanism of the three types of QASs against mycelia of R.solani was comparatively evaluated.It was found that Si_x-Q₅,PQD-BC and BC can have influence on mycelial morphology,cell wall,cell membrane?permeability and integrity?and cell internal structure?DNA and mitochondrial?,and macromolecular quaternary ammonium salt?Si_x-Q₅ and PQD-BC?can cause cell membrane lipid peroxidation uniquely.?3?Base on investigating the sclerotia of R.solani formation process,as well as the surficial and internal microstructure,confirming the sclerotia composed of hydrophobic outer layer and the inner layer contains active mycelia,we confirmed that amphiphilic macromolecular quaternary ammonium salts can change the hydrophilic and hydrophobicty of sclerotial surface.?4?The influence of the three types of QASs against the sclerotial formation and germination of R.solani was studied,it was found that there was a difference in the mechanism between the amphiphilic macromolecular quaternary ammonium salt and the small molecule quaternary ammonium salt against the sclerotial formation,and the hydrophilic macromolecular quaternary ammonium salt had little effect on the formation of the sclerotia.?5?Trough fluorescent markers,the mechanism of three types of QASs against inbihiting the sclerotial gerimination was preliminarily discussed.Furthermore,with fluorescent label,Si_x-Q₅ series were found to not only absorb effectively onto the surface of sclerotia,but also penetrate and retain stably in the sclerotial inner layer,killing the active mycelia inside.As a result,the goal of long-term and stable inhibition of sclerotial gerimination was achieved.?6?The environmental toxicity of the three types QASs were evaluated,and it was found to reduce to the environmental toxicity by polymerizing QASs as well as introducing hydrophobic blocks into QAS chains.The above results provide a useful research thought and a theoretical basis for further researches on the macromolecular antifungal agents and controlling strategies for eradicating the RshB.