Toxicity and control efficacy of tetramycin against Passalora fulva

The objective of this study is to evaluate control efficacy of tetramycin against tomato leaf mold caused by Passalora fulva (Cooke) U. Braun & Crous. Toxicities of the tetramycin on mycelium growth, conidial germination and germ tube growth of 9 strains P. fulva were determined, and the control efficacy was evaluated under field conditions. The toxicity test showed that the conidial germination and the germ tube growth of tested trains are more sensitive to the tetramycin, and EC50 values are 0.002 30-0.012 7 μg/mL, 0.000 50-0.013 μg/mL, respectively. However, the sensitivity of the mycelium growth is humble, and the EC50 values are 0.601 6-1.394 μg/mL. The observation results obtained by optical microscope demonstrated that tetramycin treatment results in abnormal phenomena of P. fulva development, including inhibited growth of young hyphae, conidial germination, increased secondary branches and bulky end of hyphae. Field trials showed that protective efficacies of the tetramycin at 6.75 and 20.25 g a.i./hm2 are 74.40% and 83.09%, whereas of the corresponding curative efficacies are 67.92% and 76.68%, respectively, which are significantly more effective than that of thiophanate-methyl 540 g a.i./hm2 treatment.