杀菌剂对核盘菌低剂量刺激作用和促致病作用机理的研究

Sclerotinia sclerotiorum is a devastating and economically important plant pathogen because of its wide host-range and difficulties in plant pathogen-resistance-breeding. According to preliminary experiments, we discovered a distinct phenomenon of hormesis that low dose dimethachlon and carbendazim could promote S.sclerotiorum fungal growth on PDA and increase pathogenicity on rapeseed (Brassica napus). To our knowledge, up to now, there has not been any report of fungicide hormesis and pathogenicity promoting on S. sclerotiorum. This project will study hormesis and pathogenicity-promoting mechanisms of low dose dimethachlon and carbendazim to S. sclerotiorum. This study will focus on the effects of low dose fungicide on pathogenicity process and on pathogenicity determinants, i.e., oxalic acid, cell wall degrading enzymes (pectinase,cellulase,etc) and necrosis and ethylene-inducing peptides (NEPs). These studies will deepen our understanding of hormesis and pathogenicity promoting mechanism, of effects of low dose fungicide on Sclerotinia stem rot occurrences in rapeseed fields, of S.sclerotiorum fungicide resistance development and will have great theoretic and practical implications for using fungicide to control S.sclerotiorum and even for other plant pathogenic fungi management.

核盘菌(Sclerotinia sclerotiorum)由于其寄主范围广泛、抗病育种困难而成为农业上一种危害严重的植物病原真菌。在实验中我们发现杀菌剂如菌核净和多菌灵等对核盘菌部分菌株的生长具有明显的低剂量刺激作用，对其在油菜上的致病性具有促进作用。目前,尚未有低剂量杀菌剂对核盘菌生长和致病力具有促进作用的报道。本项目拟就菌核净和多菌灵对核盘菌的这种低剂量刺激生长作用以及对致病力促进作用的机理进行研究，重点研究低剂量杀菌剂对核盘菌在油菜上的致病过程以及致病相关因子如草酸、细胞壁降解酶(果胶酶、纤维素酶等)、坏死及乙烯诱导肽(NEPs)等方面的影响。这些研究对深入认识杀菌剂低剂量刺激作用和促致病作用的机理、低剂量杀菌剂对田间油菜菌核病发生的影响、科学合理地利用杀菌剂防治油菜菌核病甚至对其它植物病原真菌的化学防治具有重要的理论意义和实际指导作用。

在田间，由于杀菌剂在喷施过程中的的飘移和在作物体表的降解，部分病原菌会接触到低剂量的杀菌剂。本项目研究了多菌灵、菌核净等杀菌剂对核盘菌生长和致病的刺激作用及杀菌剂对核盘菌致病刺激作用的机理。. 研究结果表明：（1）喷施多菌灵在0.1~20 mg/L浓度范围内对多菌灵抗性菌株的致病力有显著的刺激作用；最大刺激幅度20~30%。（2）菌核净在1~5 mg/L浓度范围内对核盘菌的致病力有明显的刺激作用。对敏感菌株的最大刺激幅度为20~30%，对抗性菌株的最大刺激幅度达70~80%。（3）刺激作用机制研究表明杀菌剂对核盘菌致病的刺激作用为直接刺激作用，而不是抑制后过度补偿作用。在生理机制上，刺激作用与致病相关因子草酸无关。菌核净的刺激作用与核盘菌对活性氧的耐受力增强可能有关。. 以上研究对正确认识杀菌剂的低剂量刺激作用和科学合理的使用杀菌剂具有重要意义。