The preliminary mechanism of the new rice line YSBR1 with high resistance to sheath blight disease(SB) was investigated through analyzing the content of wax and silicon, the arrangement of silicon cell, the activity of the wellknown defense enzymes, and the expression pattern of some pathogenesisrelated (PR) genes in response to SB fungus infection. The wax contents of leaves and leaf sheaths were not significantly different among varieties with various resistance levels to SB disease including YSBR1. The arrangement of silicon cells in the upper and lower surfaces of leaf blades was similar among varieties, and no silicon cell was found in the inner surfaces of leaf sheaths. In response to SB fungus infection, the contents of silicon in the lower surfaces of leaf blades and the inner surfaces of leaf sheaths in YSBR1 were significantly induced, as well as in inner surfaces of leaf sheaths of Jasmine 85 with moderate resistance to SB. However, it was not found in all tissues tested in susceptible Lemont. In YSBR1, the activities of phenylalanine ammonia lyase(PAL ) and polyphenol oxidase(PPO) were induced faster and significantly higher by SB fungus than those in other varieties. The expression level of OsPR4 in YSBR1 was upregulated rapidly and obviously higher than those in Jasmine 85 and Lemont 12 h post inoculation. The OsPR10 gene was found constitutively expressed in YSBR1 and Lemont, but induced expression in Jasmine 85 by SB fungus infection. Taken together, our results suggest that the defense system of YSBR1 is rapidly activated upon SB fungus infection,which is responsible for its high resistance to SB.
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