The Mechanism Underlying The Inhibition Of Pathogenic Fungi Of Panax Notoginseng Rot By Compound Fungicide

Panax notoginseng is a precious traditional Chinese medicine,it has good therapeutic effects on various of human diseases.The root rot disease of Panax notoginseng is caused by various pathogenic bacteria,which seriously affects the growth of Panax notoginseng and leads to low yield.However,the fungicides registered for the control of Panax notoginseng diseases are far from meeting the control needs,so farmers have to use fungicides against other plant disease for Panax notoginseng root rot,which leads to the abuse of fungicides.Therefore,it is particularly important to screen a broad-spectrum composite fungicide with synergistic effects.This article focuses on the pathogenic bacteria Fusarium oxysporum,Fusarium solani,and Alternaria alternata that cause root rot of Panax notoginseng.This study screened commonly used pesticides in the market,selected fungicides with good inhibitory effects on three types of pathogens,and compounded them in pairs.Then,indoor toxicity testing and combined toxicity testing were conducted on the composite fungicides,and the synergistic coefficient was calculated to obtain a composite fungicide with good synergistic effect.Then,a preliminary exploration was conducted on the antibacterial and synergistic mechanisms of the composite fungicide.The research results provide a broad-spectrum compound fungicide and theoretical support for the prevention and control of Panax notoginseng root rot disease.The results are as follows:After the initial screening of fungicides,the indoor toxicity test showed that thatthiram(Baofusi)and pyraclostrobin(BASF)had good inhibitory effects on F.oxysporum,with EC50 values of 0.0941 mg/m L and 0.155 mg/m L,respectively.They also had good inhibitory effects on F.solani,with EC50 values of 0.1222 mg/m L and0.1514 mg/m L,respectively.There are good inhibitory effects on A.alternat,such as trifloxystrobin·tebuconazole(nadiox),pyraclostrobin(BASF),and difenoconazole(Sili),with EC50 values of 0.0800 mg/m L,0.1038mg/m L,and 0.0753 mg/m L,respectively.Combined toxicity test of compound fungicides.When the ratio of pyrazolidinolate to difenoconazole,and the ratio of thiram to difenoconazole is 1:2.5and 1:5,respectively,the synergistic coefficients against F.oxysporum are the highest,with values of 2.32 and 2.11,all showing synergistic effects;At the ratios of 1:5,1:2.5,and 1:1,the synergistic coefficients of imidacloprid against F.solani were the highest,with values of 1.9,2.55,and 2.04,respectively.At the ratios of 1:5,1:2.5,and 5:1,the synergistic coefficients against A.alternat were the highest,with values of 1.63,1.71,and 2.04,respectively.The effect of compound fungicides on the mycelial morphology and different developmental stages of three pathogenic bacteria.The three types of pathogenic fungi treated with pyrazolidinolate showed an increase in branching and swelling of the top of the hyphae.The hyphae of three pathogenic bacteria treated with difenoconazole were not smooth and showed slight deformation.Compared with the two single agents,the three types of fungal hyphae treated with a mixture of pyrazolidinolate and difenoconazole(1:2.5)showed a significant increase in branching and the phenomenon of drying and atrophy began to occur.The spore production of F.oxysporum and F.solani treated with a combination of pyrazolidinolate and difenoconazole(1:2.5)was significantly lower than that of the single dose control,and the germination rate of the treatment was significantly lower than that of the single dose control.The dry weight of the three pathogenic fungi hyphae treated with the combination of pyrazolidinolate and difenoconazole(1:2.5)was lower than that of the single dose treatment,but the difference was not significant.The effect of compound fungicides on the energy and substance metabolism of three pathogenic bacteria.As the cultivation time increased,the NAD malate dehydrogenase activity of the three pathogenic bacteria treated with the combination of pyrazolidinolate and difenoconazole(1:2.5)was lower than that of the single dose control,and the soluble sugar content of the three pathogenic bacteria treated was higher than that of the single dose control.The combination of pyrazolidinolate and difenoconazole(1:2.5)enhances the inhibition of respiration,hinders intracellular energy metabolism,and leads to disorder of substance metabolism,thereby exhibiting synergistic effects.It is preliminarily inferred that this may be the physiological and biochemical mechanism of the synergistic effect of pyrazolidinoxystrobin combined with difenoconazole.