Abstract: In vitro detection method for sensitivity of Magnaporthe grisea to tricyclazole was studied and the potential resistance risk of M. grisea to tricyclazole was also assessed. Both EC₅₀ of hyphal melanization (EC₅₀ -H) and minimal inhibitory concentration of melanization in appressoria (MIC-A) by the inhibitor tricyclazole showed positive correlation to the EC₅₀ of tricyclazole against blast disease tested in vivo, with relative co-efficiency (R²) of 0.8995 and 0.8244, respectively. However, the stability and reproducibility of EC₅₀ -H were better than those of MIC-A, suggesting that it could be used to detect the sensitivity of M. grisea to tricyclazole in vitro. Tricyclazole sensitivity of the progenies derived from single spores of the most sensitive isolate DY2 and the least sensitive isolate GY6 detected in sensitivity monitoring study in year 2000 was not stable, with mean EC 50 values of 4.4968 μg/mL and 5.4010 μg/mL, respectively, indicating that the difference in EC₅₀ between DY2 and GY6 was possibly not caused by resistance variation. EC 50 of GY6 did not significantly increase when continuously selected for twenty generations under the selection pressure of tricyclazole in vivo. However, the sensitivity of DY2 was decreased by 10-fold after selected for twenty generations. These results suggested that tricyclazole was still at low resistance risk for M. grisea in China.

Key words: Magnaporthe grisea, tricyclazole, melanin biosynthesis, sensitivity detection, resistance risk assessment

摘要： 研究了稻瘟病菌对三环唑敏感性的离体检测技术及其潜在抗药性风险。三环唑抑制菌丝黑色素生物合成的有效中浓度（EC50H）和抑制附着胞黑色素化的最小抑制浓度（MICA）都与活体条件下三环唑防治稻瘟病的EC50有很好的相关性，相关系数（R2）分别为0.8995和0.8244。但EC50H比MICA的稳定性和重复性更好，可用于离体检测稻瘟病菌对三环唑的敏感性。在2000年抗药性检测中检测到的最敏感菌株DY2和最不敏感菌株GY6的无性单孢后代对三环唑的敏感性不稳定，平均EC50分别为4.4968 μg/mL和5.4010 μg/mL，差异不显著，说明DY2和GY6对三环唑的敏感性差异可能不是由抗药性变异引起的。DY2和GY6经过20代的活体药剂筛选后， GY6的EC50没有显著升高；但DY2的敏感性有一定的下降，EC50为初始菌株的10.0倍，说明稻瘟病菌对三环唑仍然属于低抗药性风险。

关键词: 稻瘟病菌, 三环唑, 黑色素生物合成, 敏感性检测, 抗药性风险评估