| Banded leaf and sheath blight in corn is one of the important diseases in the main corn producing areas of China,which seriously affects the quality and yield of corn and causes serious economic losses.The promotion of straw returning to the field has made the pathogens have a wider habitat,which has further aggravated the damage of banded leaf and sheath blight in corn.At present,chemical control is still the main way to prevent and cure banded leaf and sheath blight in corn.However,traditional medicines are mainly spray,it is difficult to control diseases,and the duration of pesticide retention is short.It is urgent to develop safe and efficient chemicals to control banded leaf and sheath blight in corn.But,the widespread use of chemical agents is inevitably accompanied by the problem of pathogen resistance.In the domestic,thifluzamide as a medicament for the control of sheath blight has been reported,there is good control effect,but its application in corn still needs to be evaluated.To this end,this study used the mycelial growth rate method to determine the sensitivity of 102 isolates of Rhizoctonia solani to thifluzamide in six regions of Shandong.The biological characteristics of mutants obtained by UV-induced and domestication of the drug were studied.The effects of seed dressing of thifluzamide on corn germination and seedling growth under indoor and field conditions were evaluated.The effects of thifluzamide on banded leaf and sheath blight in corn and its effect on yield under field conditions were studied.It is speculated that thifluzamide can be used as an ideal candidate for controlling banded leaf and sheath blight in corn.The main results are as follows:1、The sensitivity of 102 isolates of R.solani to thifluzamide was determined using the mycelial growth rate method.It was shown that R.solani was highly sensitive to thifluzamide.The differences in the sensitivity of the isolate of Tai’an,Linyi,Weifang,Laiwu,Rizhao and Qingdao to thifluzamide were not significant.The coefficients of variation were 10.26,5.15,11.31,6.29,5.68 and 6.51;isolates from six regions are low to moderate resistant isolates.With an EC50 range of 0.0103-0.1942 and an EC50 average value of 0.086±0.004μg/mL.The skewness=0.298,kurt=-0.298,and p=0.0884>0.05,which agrees with continuous skewed normal distribution and the sensitivity frequency distribution had a continuous unimodal curve.It can be used as the baseline sensitivity of R.solani in corn to thifluzamide in the Shandong region.Linear correlation analysis between the EC50 values of thifluzamide and eight other fungicides revealed that there was no interaction sensitivity between thifluzamide and some other fungicides,including tebuconazole,propiconazole,fludioxonil,validamycin,difenoconazole,carbendazim,boscalid and penflufen.2、Five drug-resistant isolates were obtained by UV induction and one resistant mutant was obtained by drug domestication.Their resistance levels ranged from 6.46 to 20.08.The mutation frequencies were 0.87%and 0.52%,respectively.Five drug-resistant isolates obtained by UV induction could not be stably inherited.While one mutant QD2-Y4 obtained by acclimation of the drug could be stably inherited.Studies on the biological traits of antagonistic mutants showed that the mycelial growth rate of TA3-X2 isolate was higher than that of the parent isolates and the remaining mutant isolates are not significantly different from the parental isolates.The dry weight of mycelium and the dry weight of sclerotia of the five resistant isolates and one resistant mutant were all lower than the parent isolates.The pathogenicity of TA3-X2,WF6-A2 and QD2-Y4 was lower than that of the parent isolates.However,the pathogenicity of TA17-X6,LY8-3 and QD14-Y7 was not significantly different from that of the parental isolates.There was no cross-resistance between thifluzamide and some other fungicides,including tebuconazole,propiconazole,fludioxonil,validamycin,difenoconazole and carbendazim.However,the cross-resistance among thifluzamide,boscalid and penflufen was observed.3、According to the sand culture test,24%thifluzamide FS is safe for corn in the amount of 6 g a.i.100 kg-1 seed-96 g a.i.100 kg-1 seed,and can increase the germination rate,germination potential,germination index and vitality index of maize seedlings.However,when the dosage was too high,192 g a.i.100 kg-1 seed had adverse effects on the plant height,root length and fresh quality of the seedlings,and all indexes were lower than the blank control.The greenhouse pot experiment showed that the amount of 24%thifluzamide FS was6 g a.i.100 kg-1 seed-48 g a.i.100 kg-1 seed could increase the root vigor and chlorophyll content of potted corn.The dosage of 24 g a.i.100 kg-1 seed promoted the best effect,the root vigor increased by 78.0%compared with the blank control,and the chlorophyll content increased by 32.3%compared with the blank control;The results of the efficacy test of greenhouse inoculation fungi showed that the control efficiency of each dose on banded leaf and sheath blight in corn were higher than 60%.The dosage of 24%thifluzamide FS was 48 g a.i.100 kg-1 seed had the best control effect,reaching 87.43%.The dosage of 6 g a.i.100 kg-1seed had the worst control effect,so the dose was no longer tested in the field.4、Field experiment results showed that 24%thifluzamide FS dosage in 12 g a.i.100 kg-1seed-48 g a.i.100 kg-1 seed promoted maize seedling and seedling growth to different degrees,increased seedling rate,plant height,stem diameter,main root length,number of roots,fresh weight and root-shoot ratio.The study found that 24%thifluzamide FS and 60 g/L tebuconazole FS can increase the ear length,ear diameter,number of rows,grain number per ear,100-grain weight and plot yield of corn,thereby increasing corn production.In 2017 and2018,the most obvious effect of 24%thifluzamide FS was 48 g a.i.100 kg-1 seed,which increased yield by 15.72%and 14.11%.The field control effect of corn sheath blight in2017-2018 showed that the control effect of 24%thifluzamide FS in the dosage of 48 g a.i.100 kg-1 seed in the small bell stage of the corn to the wax-ripeness stage was above 40%. |
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