Sensitivity of 10 common fungicides to Rhizoctonia solani and their synergistic effects

【Objective】Screening the fungicide combinations that had a strong synergistic action on Rhizoctonia Solani and providing a new theoretical basis for filed control of synergistic action and developing synergism combinations against R.solani.【Method】R.solani was the material.The mycelial growth rate method was used to determine the virulence of ten fungisides(eight methoxyacrylate fungicides such as azoxystrobin, picoxystrobin and pyraclostrobin, and two kinds of triazole fungicides including propiconazole and difenoconazole) to R.solani.The synergistic effect of propiconazole·trifloxystrobin combination to R.solani was determined by mycelium growth rate method.The effects of the combination on the physiology and biochemistry of R.solani were evaluated by conductivity method, soluble protein kit, superoxide dismutase(SOD) kit and peroxidase(POD) kit.And the field experiment was conducted in August, 2019 to evaluate the field control effects of 250 g/L propiconazole EC, 50% trifloxystrobin WDG and combinations(effective mass ratio of 250 g/L propiconazole EC to 50% trifloxystrobin WDG was 1:5) on rice sheath blight disease.【Result】The results showed that the ten fungicides had high sensitivity to R.solani.The EC₅₀ range was 0.20-1.61 μg/mL.Among them, the virulence of pyraoxystrobin and kresoxim-methyl was relatively weak.And the other eight fungicides had better inhibitory activity on the mycelial growth of R.solani, their EC₅₀ were all less than 1.00 μg/mL.The virulence of pyraclostrobin was the strongest with EC₅₀ of 0.20 μg/mL.Propiconazole and trifloxystrobin had better synergistic effects on R.solani when the effective mass ratios were 1:5, 1:10 and 5:1.Among them, the synergism was the most obvious when the effective mass ratio was 1:5.Its EC₅₀ value was 0.24 μg/mL and cotoxicity coefficient(CTC) value was 393.41.Furthermore, the combination could increase the permeability of cell membrane, inhibit the synthesis of protein and decrease the activity of superoxide dismutase(SOD) and peroxidase(POD) after the treatment.After 21 d of field spraying the synergistic combination of 250 g/L propiconazole EC and 50% trifloxystrobin WDG, the control effect of rice sheath blight was 94.08%, which was higher than that of single application of propiconazole EC(88.79%) and 50% trifloxystrobin WDG(92.72%).【Conclusion】The results show that the combination of propiconazole·trifloxystrobin has a better synergistic effect on R.solani.It has good control effect on rice sheath blight, and can greatly reduce the dosage of fungiside, and has the potential to be developed into a combination preparation for rice sheath blight.