Study On The Sensitivity Of Rhizoctonia Solani To Common Fungicides And Its Controlling Disease

Sheath blight is a serious disease in rice production,which occurs throughout the world.Plant damage has a great impact on rice yield.At present,application of chemical fungicides is main means for controlling the disease.However,it is unclear whether the sensitivity of Rhizoctonia solani(R.solani)to common fungicides has changed and fungicide resistance has occurred in Northeast,China.In this paper,the sensitivity of R.solani to common fungicides was determined and the sensitivity baseline was established.The compound synergistic fungicides were screened for controlling rice sheath blight(RSB),and the mechanism of compounding synergistic fungicide against RSB was initially studied.The main results are as follows:1.Establishing sensitive baseline of R.solani to common fungicidesMycelium growth rate method was adopted to test the sensitivity of R.solani to difenoconazole,prochloraz,hexaconazole,coumoxystrobin,trifloxystrobin,azoxystrobin,thifluzamide and shenqinmycin.The rusults showed that the sensitivity baselines of the eight fungicides to R.solani was 29.3614,19.8194,0.0782,0.1594,0.0690,0.2322,0.4055,and37.6184 mg/L,respectively.There was a differences in the sensitivity of R.solani among regions to difenoconazole,coumoxystrobin,azoxystrobin and thifluzamide and relevance between the isolates geographical origin and their sensitivities to coumoxystrobin,azoxystrobin and thifluzamide fungicides.The sensitivities of strains to fungicides were positively correlation between coumoxystrobin and trifloxystrobin(y = 0.1179 + 0.2012 x,P =0.031 <0.05)and trifloxystrobin and azoxystrobin(y = 0.7626 x + 0.1252,P = 0.001 <0.05)with the same mechanism of action.The negative correlation between prochloraz and shenqinmycin(y =-0.6768x+49.2510,P = 0.03 < 0.05),coumoxystrobin and hexaconazole(y=-0.4573x+0.2960,P = 0.001 < 0.05)was detected.And there was not significantly correlation between the other fungicides.2.Screening mixture fungicidesFive fungicides were chosed to mix,and the results showed that the mixture of differentratios of shenqinmycin and coumoxystrobin has antagonistic effect on R.solani.The mixtures of hexaconazole and shenqinmycin at concentration according to 3:2(SR=7.99),isoprothiolane and thifluzamide at concentration according to 4:1(SR=22.30)were the most obvious inhibition of mycelial growth,respectively.According to the results of indoor virulence determination,isoprothiolane and thifluzamide(quality ratio=4:1)was made into 25% isoprothiolane and thifluzamide water-dispersible granules(WG).Field trials showed that the control efficacy of 100 g/667 m~2 25% isoprothiolane and thifluzamide WG against RSB reached 82.73%.3.Study on the mechanism of the mixture fungicides control of R.solaniThe effects of the mixtures of isoprothiolane and thifluzamide on the protective and curative effects,mycelial morphology,sclerotia germination and sclerotia pathogenicity of R.solani were studied.The results indicated that the concentration of mixture fungicide was 100mg/L,the protection and curative effects on RSB reach 80.12% and 61.45%,respectively.And the mixture of isoprothiolane and thifluzamide at quality according to 4:1 was the most obvious inhibition of mycelial growth of R.solani,but was not inhibition for sclerotium germination.The mixture inhibited the sclerotium pathogenicity and the mycelial respiration of R.solani.The mycelium morphology were distorted and slight folds appeared on the surface of the mycelium.