Inhibitory Effect And Mechanism Of Polysiloxane-Polyquaternary Ammonium Salt Block Copolymer On Banana Fusarium Wilt

Banana Fusarium wilt is a serious soil-borne vascular disease,it is caused by Fusarium oxysporum f.sp.Cubense（Foc）,of which tropical race 4（Foc4）is the most destructive.The pathogen is difficult to control because Foc4 can survive for many years and invade repeatedly,so killing the pathogen in the soil and resisting the continuous invasion of spores is one of the effective methods.Aiming at the characteristics of pathogenic spores living in soil,this paper aims to find quaternary ammonium salts which can play a role in soil.Using the macromolecular quaternary ammonium salt synthesized by our research group and the commercially available small molecular quaternary ammonium salt as the research objects.The three types of quaternary ammonium salts are amphiphilic macromolecular quaternary ammonium salts（polydimethylsiloxane-b-poly（dimethylaminopropyl methacrylate-benzyl ammonium chloride）block copolymers,PDMS-b-QPDMAEMA,abbreviated as S_nQ₅）,macromolecular quaternary ammonium salts homopolymers（polydimethylaminopropyl methacrylamide-benzyl ammonium chloride,PQD-BC）,and dodecyl dimethylbenzyl ammonium chloride（BC）:（1）The inhibition properties of these three quaternary ammonium salts on Foc4mycelium growth and spore germination were studied.It was found that although the concentration of small molecular quaternary ammonium salts was the smallest and the killing effect of the three quaternary ammonium salts was rapid,the S_nQ₅action rate was the fastest,followed by PQD-BC,and finally BC.（2）Microscopic observations shows that quaternary ammonium salt with fluorescent group can quickly enter the inside of Foc4spores,and the quaternary ammonium salt entering spores is difficult to dissociate,and it is observed under microscope that macromolecular quaternary ammonium salt is more likely to break Foc4 spores.（3）The quaternary ammonium salt can act on the cell wall and affect the hydrophobicity of the spore surface and the composition of the cell wall.（4）Soil adsorption and leaching tests show that quaternary ammonium salts are not easily lost in soil;（5）When there is Foc4 in the soil,S_nQ₅can kill spores that constantly invade the soil;and when there is no pathogen,S_nQ₅can maintain a 90 d retention period in the soil,indicating its stable nature in the soil.（6）In the range of experimental concentrations,S_nQ₅can inhibit the growth of actinomycetes in soil as a whole and stimulate the growth of bacteria and fungi,with the highest growth rate of bacteria;high-throughput sequencing shows that some fungi,including Fusarium,are inhibited and some Pichia fungi are stimulated;dehydrogenase and luciferase diacetatease activity in soil is under the action of S_nQ₅,but catalase activity is increased.（7）Pot experiments show that S_nQ₅can reduce the infection of Foc4 on plantain seedlings and do not produce harm to plantain seedlings.The above research work provides new ideas and methods for the prevention and treatment of banana Fusarium wilt by macromolecular quaternary ammonium salt.