Abstract: ObjectiveEffects of different salicylic acid(SA)concentrations on the morphological development of rice blast fungus and the expression of defense-related genes in infected rice were studied,and mechanism of SA on inter-action of biotrophy-associated secreted protein 4(BAS4)in rice blast and rice was revealed to lay a theoretical foundation for effective control of rice blast in cultivation.MethodMagnaporthe oryzae overexpression strain(35S:BAS4/Mo-1)and wild strain(A1343R-7)were pretreated by SA of various concentrations(50,100,200,500,1000 and 2000 μmol/L). Colony growth,spore number,spore germination and appressorium formation of overexpression strain and wild strain were analyzed.The incidence of rice inoculated by M.oryzae which was pretreated by 200 μmol/L SA was investigated, and rice defense-related genes expression in infected rice was analyzed by real-time fluorescence quantitative PCR(qRT-PCR).ResultThe effects of SA concentrations on the colony growth,spore number,spore germination and appressorium formation of overexpression strain were less than those on the wild strain.Disease incidence of rice inoculated by over-expression strain pretreated with 200 μmol/L SA decreased,but the range was smaller than those inoculated by wild strain pretreated with 200 μmol/L SA.After treated by 200 μmol/L SA,the expression level of pathogenesis-related gene PR1a in overexpression strain upregulated at early stage and the expresion was effective at 72 h.At the same time,expression of SA-path gene PAL downregulated,and JA-path gene AOS2 upregulated its expression at early stage,expression of gene LOX2 downregulated at all time points;expression of gene PR5 upregulated at early stage and downregulated sharply at later stage;gene HSP900 upregulated its expression at early stage,but it was lower than the expression of rice infected by wild strain.ConclusionBAS4 overexpression strain is highly resistant to exogenous SA stimulation.