Comparison of the Sensitivity of Alternaria solani Which Causing Tomato Late Blight to Seven Fungicides and Its Baseline-sensitivity to Difenoconazole

Totally seven fungicides were tested for their antifungal activity to Alternaria solani which causing tomato late blight by mycelial lineal growth method and spore germination method in vitro. The results showed that the aromatic hydrocarbon fungicide chlorothalonil with the highest activity on its spore germination and relatively high activity on mycelial growth. The benzimidazole fungicide carbendazim has very low activity both on mycelial growth and spore germination. Dicarboximides iprodione and procymidone were both effective on the mycelial growth and spore germination. The triazole fungicide difenoconazole has the highest activity on mycelial growth among these fungicides, while with very low activity on spore germination. Strobilurin fungicides kresoxim-methyl and azoxystrobin were effective on spore germination but with low effective on mycelial growth. Meanwhile, sixty field Alternaria solani strains which were collected from Hubei and Shandong were tested for their sensitivities to difenoconazole by mycelial lineal growth method, the results showed that these strains were all sensitive to difenoconazole, there was no strain was found with sharply decreased in sensitivity, therefore, the averaged EC50 value (0.3050±0.1361) mg/L could be used as the baseline-sensitivity of Alternaria solani to difenoconazole.