Bilogical Activities Of Three Fungicides Against Fusarium Fujikuroi

Rice is one of the world’s three major food crops and has the longest history in the rice genus.Rice bakanae disease is a worldwide fungal disease caused by Fusarium fujikuroi,which has a wide distribution,high frequency and high degree of damage on rice.It can not only reduce grain yield but cause quality decline,and has become the main disease on rice.To control rice bakanae disease,fungicides were widely used in recent decades.Application of fungicides played an important role in controlling the disease.But the resistance problem of F.fujikuroi to fungicides successively came out which caused the control effect was greatly reduced.It is necessary to screen alternative fungicides for management of resistance.Through the previous screening,we found that penconazole,fluazinam and pydiflumetofen have good inhibitory activity on F.fujikuroi in vitro.The isolates used in this study were isolated from diseased young rice of different fields in Shaoxing of Zhejiang Province and Huaian of Jiangsu Province in 2016.The baseline sensitivity of Fusarium fujikuroi to penconazole,fluazinam and pydiflumetofen established by the mycelial growth rate method showed that the distributions of EC50 values of penconazole,fluazinam and pydiflumetofen on 108 isolates,103 isolates and 100 isolates were 0.0782～0.8886 μg/mL,0.0621～0.5446 μg/mL and 0.0125～0.1118 μg/mL respectively.The average EC50 values were 0.3122±0.0170 μg/mL,0.203 8±0.0099 μg/mL and 0.0503±0.0029 μg/mL respectively.The above sensitivity baseline was unimodal curve,and no resistant strain to above fungicides was found.The result shows that above fungicides have strong inhibitory activity against mycelial growth of Fusarium fujikuroi.The baseline sensitivity of Fusarium fujikuroi to fluazinam and pydiflumetofen established by conidium germination method showed that the distributions of EC50 values of fluazinam and pydiflumetofen on 103 isolates and 100 isolates were 0.1006-0.9763 μg/mL and 0.0001～0.0245 μg/mL respectively.The average EC50 values were 0.3552±0.0181 μg/mL and 0.0038±0.0005 μg/mL respectively.The above sensitivity baseline was unimodal curve,and no resistant strain to above fungicides was found.The result shows that the two fungicides have strong inhibitory activity against the conidium germination of F.fujikuroi.The results of physiological effects of penconazole,fluazinam and pydiflumetofen on Fusarium fujikuroi showed that both EC50 concentration and EC90 concentration of penconazole and pydiflumetofen increased offshoot of top of hyphae of F.fujikuroi,hyphae were contorted after EC50 concentration of fluazinam treatment,the EC90 concentration of fluazinam can increase the mycelial offshoot of top;all EC50 concentration and EC90 concentration of three fungicides can reduce the spore production,damage the cell membrane and increase the cell membrane permeability,reduce the activity of peroxidase(POD).But these three fungicides had no effect on the content of erxopolysaccharides(EPS)of F.fujikuroi,and had no effect on cell wall and nuclear localization of F.fujikuroi.By observing the ultrastructure of cells after these three fungicides treatment respectively,the cell membrane structure was damaged and the organelles were disintegrated.In the safety of fungicides to rice test,rice seeds treated with 20 μg/mL,50 μg/mL,100 μg/mL and 200 μg/mL penconazole were not significantly different in germination rate,plant height and fresh weight from untreated rice,rice seeds treated with 400 μg/mL,800 μg/mL,and 1600 μg/mL fluazinam and pydiflumetofen were not significantly different in germination rate,plant height and fresh weight from untreated rice.This test proved that penconazole,fluazinam and pydiflumetofen were safe to rice.