Abstract:

【Objective】 The objective of this study is to evaluate the potential efficacy of pyraclostrobin as well as tebuconazole, propiconazole and flusilazole against tomato crown and root rot, which caused by Fusarium oxysporum f. sp. radicis-lycopersici. 【Method】The laboratory toxicity of 4 fungicides to mycelial growth, conidial germination and germ tube elongation of F. oxysporum f. sp. radicis-lycopersici were determined by mycelial growth rate and conidial germination methods. In greenhouse pot experiment, the root-irrigation method was used to treat tomato seedlings. At 7 d and 15 d after treatment, the increment of plant height and stem diameter was measured to evaluate the safety of fungicides on tomato seedlings. In the laboratory, the method of first inoculating and then applying fungicides was adopted. The control efficacy of fungicides on tomato crown and root rot at 7, 15 and 30 d after application was investigated, respectively. In field experiment, same root-irrigation method was used to investigate the incidence of tomato crown and root rot at 60, 90 and 150 d after treatment and the tomato yield statistic, and to evaluate the efficacy of fungicides against the disease in field and the effect on yield of tomato.【Result】Pyraclostrobin showed high toxicity to mycelial growth, conidial germination and germ tube elongation of F. oxysporum f. sp. radicis-lycopersici, with EC₅₀ of 0.055, 0.012 and 0.010 μg·mL ^-1, followed by propiconazole, EC₅₀ was 0.058, 0.060, 0.011 μg·mL ^-1, respectively. The inhibitory effect of tebuconazole on mycelial growth was strong, and the toxicity of tebuconazole to conidial germination and germ tube elongation was relatively low, with EC₅₀ of 0.075, 0.255 and 0.455 μg·mL ^-1, respectively. The toxicity of flusilazole to conidial germ tube elongation was high, but the toxicity of flusilazole to mycelial growth and conidial germination was low, with EC₅₀ of 0.013, 0.078 and 0.457 μg·mL ^-1, respectively. Tebuconazole at 25, 50 mg a.i./plant, propiconazole at 5, 10 mg a.i./plant and flusilazole at 5, 10 mg a.i./plant significantly inhibited tomato seedling height and increased stem diameter, but pyraclostrobin at 30, 60 mg a.i./plant had no effect on tomato seedling. In greenhouse pot experiment, 30 days after treatment (DAT), pyraclostrobin had the highest control efficacy (87.12%) on this disease at 60 mg a.i./plant, followed by propiconazole 10 mg a.i./plant, the control efficacy was 82.17%, and the control efficacy of tebuconazole at 50 mg a.i./plant and flusilazole at 10 mg a.i./plant was 79.40% and 71.67%, respectively. At 90 DAT in field experiment, the best control efficacy on the disease was 90.36% by pyraclostrobin at 60 mg a.i./plant, followed by tebuconazole at 50 mg a.i./plant and propiconazole at 10 mg a.i./plant, which was 84.20% and 82.55%, respectively. The lowest one was flusilazole at 5 mg a.i./plant (65.06%). At 150 DAT, the control efficacy of each treatment on the disease significantly declined, just tebuconazole at 50 mg a.i./plant was 40.40%. According to field statistics, pyraclostrobin at 60 mg a.i./plant had the highest yield in field, the increased production rate was 50.63%, and propiconazole at 5 mg a.i./plant was the lowest, with the rate of -2.61%. 【Conclusion】Pyraclostrobin, tebuconazole, propiconazole and flusilazole had similar toxicity on F. oxysporum f. sp. radicis-lycopersici mycelial growth, however, pyraclostrobin had higher toxicity on the conidial germination and germ tube elongation of the pathogen than the other three fungicides. Pyraclostrobin, propiconazole and tebuconazole could be used to control tomato crown and root rot in greenhouse. The control efficacy of pyraclostrobin at 60 mg a.i./plant was the highest, which was safe and increased production significantly. However, the dosages of propiconazole and tebuconazole should be concerned before application.

Key words: tomato crown and root rot, pyraclostrobin, triazole fungicide, toxicity, control efficacy