Bioactivity And Synergism Of Several Fungicides Against Magnaporthe Oryzae And Rhizoctonia Solani

Rice blast caused by Magnaporthe oryzae and sheath blight caused by Rhizoctonia solani are two major diseases threatening the safety of rice production.In addition to the selection of resistant varieties and reasonable agronomic measures,the use of fungicides for chemical control is an important measure for emergency control of these two diseases.It is an important production demand to study the synergistic combination application technology of fungicides with different action modes to reduce the dosage of fungicides and the risk of resistance.In this paper,we studied the preventive and therapeutic effects of common rice fungicides Jinggangmycin,pyrazoxystrobin,tricyclazole,isoprothiolane and fenoxanil on rice blast and their effective medium dose ED₅₀values.The results showed that the protective and therapeutic effects of pyrazoxystrobin were significantly better than other fungicides.Tricyclazole and isoprothiolane had good protective effects,but tricyclazole had almost no therapeutic effect.Jinggangmycin was combined with other four fungicides in different proportions to determine the protective and therapeutic effects and analyze the synergistic effect of various formulations.The results showed that the combination of Jinggangmycin and pyrazoxystrobin at the ratio of 1:3,1:1,10:1 and 30:1had synergistic effect on the prevention of rice blast,and the synergistic coefficient of 1:1composition was the highest,reaching 8.25.When Jinggangmycin and tricyclazole were used in the ratio of 1:5,1:3 and 10:1,they all had synergistic effect on the prevention of rice blast,and the synergistic effect of 1:5 was the largest,with the synergistic coefficient of15.5.The combination of Jinggangmycin and isoprothiolane at the ratio of 1:1,3:1 and 5:1had synergistic effect on the prevention of rice blast.The combination of Jinggangmycin and fenoxanil in five proportions all had synergistic effect on the prevention of rice blast.After 24 hours of inoculation,they were treated with the above fungicide combinations.The results showed that the five compositions of Jinggangmycin and pyrazoxystrobin all had synergistic effect,and the synergistic coefficient of the composition of 10:1 was the highest,reaching 9.41;When Jinggangmycin was combined with tricyclazole in the ratio of1:5,1:3,or with isoprothiolane in the ratio of 1:5,1:1,3:1,10:1,it also had synergistic effect;The five compositions of Jinggangmycin and fenoxanil have synergistic effect,and the synergistic coefficient of 1:5 composition is as high as 6.02.The synergistic mechanism of Jinggangmycin and pyrazoxystrobin and Jinggangmycin and isoprothiolane 1:1combination was further studied.The results showed that the two combinations could inhibit the sporulation of Magnaporthe oryzae,inhibit the respiration of mycelia and increase the permeability of cell membrane.Jinggangmycin,pyrazoxystrobin and thifluzamide had good control effect on rice sheath blight,among which pyrazoxystrobin had the best protective and therapeutic effect.Although thifluzamide had good protective effect,its therapeutic effect was weak.When Jinggangmycin was combined with pyrazoxystrobin or thifluzamide in different proportions,the synergistic coefficients of Jinggangmycin and pyrazoxystrobin 1:3 and 1:1 against sheath blight were 2.64 and 1.89 respectively;The formula composition of Jinggangmycin and thifluzamide in the ratio of 1:10,1:3,3:1 and 10:1 has synergistic effect,and the synergistic coefficient of the composition in the ratio of 3:1 is the highest,reaching 2.88.The combination of Jinggangmycin and pyrazoxystrobin had no synergistic effect on the therapeutic effect;The combination of Jinggangmycin and thifluzamide in the ratio of 1:10,1:3,1:1,1:3 and 1:10 has synergistic effect on the therapeutic effect,and the synergistic coefficient of 1:3 is as high as 5.6.The 1:3 combination of Jinggangmycin and pyrazoxystrobin and the 3:1 combination of Jinggangmycin and thifluzamide can significantly increase the inhibition of sclerotia development and mycelial respiration of Rhizoctonia solani,and increase the permeability of cell membrane.The results showed that the combination of Jinggangmycin and pyrazoxystrobin had the best control effect on Rice Blast,and the synergistic effect was the most obvious.The combination of Jinggangmycin and tifuramide had good control effect on rice sheath blight,and Jinggangmycin still had good control effect when it was the main component.The synergistic mechanism of Jinggangmycin and pyrazoxystrobinat the ratio of 1:1 and Jinggangmycin and pyrimethanil at the ratio of 1:1 against rice blast,and the synergistic mechanism of Jinggangmycin and pyrazoxystrobin at the ratio of 1:3 and Jinggangmycin and thiafuramide at the ratio of 3:1 against rice sheath blight were preliminarily explored.