Sensitivity Detection Technique and Resistance Risk Assessment of Magnaporthe grisea to Tricyclazole

In vitro detection method for the sensitivity of Magnaporthe grisea to tricyclazole was studied, and the potential resistance risk of blast disease to tricyclazole was assessed. Both EC₅₀ of hyphal melanization (EC₅₀-H) and minimum inhibitive concentration of melanization in appressorial (MIC-A) by 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, 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 in 2000 was not stable, with mean EC₅₀ values of 4.4968 μg/mL and 5.4010 μg/mL, respectively, indicating that the difference in EC₅₀ between DY2 and GY6 was not caused probably by resistance variation. EC₅₀ of GY6 did not increase significantly 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. The results suggested that tricyclazole was still low resistance risk for M. grisea in China.