两亲性大分子季铵盐的合成及其对水稻纹枯病菌的抑制作用与机理

Rhizoctonia solani is hard to be eradicated because it can resist the existing fungicides in the form of sclerotium. According to the asexual reproduction of R. solani, i.e., from mycelium to sclerotium and to mycelium again, and also the typical inner-outer layers structure of R. solani sclerotia, a novel amphiphilic macromolecular containing quaternary ammonium salt (PDMS-b-PQAS), with polydimethylsiloxane (PDMS) as the hydrophobic block, and polymers containing quaternary ammonium salt as hydrophilic block, was designed and synthesized. PDMS-b-PQAS could act as both macromolecular surfactant and macromolecular fungicides, thus it could stably absorb on the surface of sclerotia based on the hydrophilic-hydrophobic interaction, then the hydrophobic outer layer of the sclerotia were soaked and infiltrated by both water and the macromolecular surfactant, i.e., PDMS-b-PQAS, and the inner mycelium could be inhibited or destroyed by the infiltrated PDMS-b-PQAS, thus the R. solani sclerotia germination could be effectively inhibited. The core of this project including four parts, firstly, the inhibition effect of PDMS-b-PQAS on R. solani would be extensively studied; secondly, the relationship between polymer structure and adsorption/soaking characteristics on the complex surface of simulating solids would be established; and thirdly, the structure-properties relationship among PDMS-b-PQAS structure and its adsorption, soaking and infiltrating characteristics on the surface of the R. solani sclerotia, and the inhibition of sclerotium germination would be established; at last, a novel method for the eradication of rice sheath blight based on the above mentioned structure-properties relationship and the pot/field experiments would be carefully explored and put forward, which could also provide scientific evidences for the permanent prevention and control of rice sheath blight.

水稻纹枯病（R. solani）以“菌丝-菌核-菌丝”无性繁殖，且以菌核的形式抵御现有药剂的作用，使得难以根治。本项目根据水稻纹枯病菌核的内外层组成与结构特性，设计合成了一类以聚硅氧烷（PDMS）为疏水嵌段、含季铵盐侧基的聚合物（PQAS）为亲水嵌段、兼具大分子表面活性剂和大分子杀菌剂特性的两亲性大分子季铵盐（PDMS-b-PQAS），它可通过亲-疏水作用稳定吸附在菌核表面，继而浸润、渗透菌核的疏水性外层，抑制/破坏菌核萌发初期产生的菌丝及菌核内层活性菌丝，实现对该病菌核萌发的有效抑制。在研究PDMS-b-PQAS对水稻纹枯病菌丝的抑制机理及其在模拟复杂固体表面的吸附与浸润特性的基础上，通过建立两亲性大分子季铵盐的结构及其在菌核表面的吸附与渗透特性、对菌核萌发的抑制作用三者之间的结构-性能关系，结合盆栽与田间试验，为探索水稻纹枯病的根治新方法提供理论依据。

水稻纹枯病菌（Rhizoctonia solani）的菌核是其无性繁殖中的一种特殊形态，现有防治方法难以对R. solani菌核进行有效防治是水稻纹枯病难以根治的重要原因之一。本项目以抑制R. solani菌核萌发为目标，在系统研究菌核微观结构的基础上，设计、合成了一系列不同结构的大分子季铵盐，以期通过建立“大分子结构-抑菌活性-抑制菌核萌发-环境毒性”构效关系，筛选出对菌丝及菌核具有低毒高效的大分子季铵盐类药物。主要研究内容及其结果包括：. （1）合成了一系列含聚硅氧烷嵌段的两亲性大分子季铵盐（PDMS-b-QPDMAEMA，SnQ5），发现PDMS嵌段长度适中时（~5 kDa）的SnQ5抑菌活性最佳：既可有效吸附在菌核表面、又可渗透进入并稳定存留于菌核内部，杀死菌核内层的活性菌丝，且不易被冲洗流失，从而实现对菌核萌发的长效稳定抑制；在此基础上初步建立了“SnQ5结构-抑制菌核萌发”构效关系；盆栽和田间试验结果表明，经SnQ5处理的菌核，其为害水稻植株的能力明显下降。. （2）合成一系列主链型亲水性大分子季铵盐、聚二烯丙基季铵盐，并探索了其对R. solani抑制特性及其环境毒性。. （3）在SnQ5的基础上，进一步设计、合成了一类合成路线更简便的聚硅氧烷接枝伯胺盐酸盐（PDMS-g-AH），发现其对R. solani有较高的抑制活性，且对菌核萌发有良好的抑制作用，并可干扰菌核的正常形成，延长菌核发育阶段，使得形成菌核的数量与总干重明显减小。. （4）SnQ5、PDMS-g-AH与丙烯酰胺季铵盐均聚物（PQD-BC），均能引起R. solani细胞膜发生脂质过氧化，其机理仍待进一步研究。. （5）季铵盐的大分子化及疏水嵌段的引入，有利于增加其在土壤中的吸附作用，减少药物的淋溶，有效降低环境毒性。. 上述研究结果对水稻纹枯病的长效防治提供了新思路和新方法。