Studies On The Growth-promoting And Disease-preventing Mechanism Of Codonopsis Pilosula Root Rot Biocontrol Bacteria

Codonopsis(Codonopsis pilosula)is a herbaceous plant in the Campanulaceae family,which is a commonly used Chinese medicinal material.In recent years,codonopsis root rot has been severely affected in Lintao County,Weiyuan County,and Longxi County,which has a huge impact on the quality and yield of codonopsis.Codonopsis root rot is mainly controlled by crop rotation and chemical fungicide,but its control effect is very low.For this reason,the use of biocontrol bacteria to prevent root rot of codonopsis has become a new method.In this study,the isolated root rot pathogens and biocontrol bacteria of Codonopsis pilosula were used as the research objects,and the control effect and mechanism of biocontrol bacteria were studied.The research results of this paper were as follows:1.Collect samples of codonopsis root rot from Weiyuan County,Gansu Province.Through the isolation and identification of the pathogen,Fusarium oxysporum was finally determined to be the pathogen of codonopsis root rot.The strain YF,which has a strong inhibitory effect on the root rot pathogen of codonopsis,was isolated from the compost of sheep manure.The gene analysis of the strain YF confirmed that YF was Paenibacillus polymyxa.2.Through the optimization of biocontrol bacteria YF medium,the optimal carbon source,nitrogen source,and inorganic salt were determined to be sucrose,peptone,and magnesium sulfate,respectively,and the orthogonal test method was used to finally determine the optimal medium for YF:chlorine 3 g of sodium,15 g of sucrose,5 g of magnesium sulfate,15 g of peptone,1L of water.After optimization,the fermentation broth(sterile)of the biocontrol bacterium YF was added to the culture medium to significantly inhibit the growth of F.oxysporum hyphae;the spore germination rate of the 10%biocontrol bacterium YF fermentation filtrate treatment group was only 14%.The pot experiment results showed that the biocontrol bacteria YF had a control effect of 89.2%and carbendazim had a control effect of 66.5%.The therapeutic effect and preventive effect of the biocontrol bacteria YF were measured.The results showed that the preventive effect of preventive treatment was 100%,and the preventive effect of therapeutic treatment was 83%.The plant growth hormone test proved that the biocontrol bacterium YF secreted IAA,and the plant height,root length,root fresh weight and root dry weight of codonopsis after applying the biocontrol bacterium YF were higher than those of the blank control group.In order to further determine the control and growth-promoting effects of biocontrol bacteria YF on codonopsis,the field test results show that the biocontrol bacteria YF fermentation broth 100-fold dilution has the best growth promotion and disease prevention effects,and the survival rate of codonopsis was the highest.It is 52.07%.The root fresh weight and dry weight are the largest,966.7 g/m~2and 310 g/m~2respectively.3.Study on the antibacterial mechanism of P.polymyxa YF:Firstly,the pGFP4412plasmid was introduced into P.polymyxa YF to form a green fluorescently labeled strain,and then the labeled strain YF-pGFP was inoculated into the root soil of codonopsis by irrigating the roots.A few days later,a laser was used to Focusing microscope detection of codonopsis root strain YF-pGFP showed that it could colonize the root epidermis of codonopsis.After 20days,the colonization amount of strain YF-pGFP was observed to decrease in root epidermis.Secondly,using enzyme activity plate detection found that strain YF can produce amylase,protease,glucanase,cellulase,and chitinase.The presence of these enzymes can effectively inhibit pathogenic fungi.Third,the crystal violet staining method was used to quantitatively determine the formation of biofilm formed by strain YF.The results showed that the latent biofilm formed after 72 hours of growth in the medium,the calculated SBF was 1.406,which confirmed that P.polymyxa YF can form SBF.Fourth,the changes of peroxidase(POD)and phenylalanine ammonia lyase(PAL)and other resistant enzyme activities were measured on the 10th day after P.polymyxa YF treated codonopsis.The PAL enzyme activity increased compared with the control group.3.15 times,POD activity increased by 42.86%.It proves that P.polymyxa YF can promote the improvement of codonopsis defensive enzymes,and indirectly improve the disease resistance of codonopsis.Fifth,after treatment with P.polymyxa YF,the main toxin produced by F.oxysporum was measured,and the toxin content of the treatment group and the control group was calculated by the standard of F.oxysporum.The results showed that P.polymyxa YF can significantly inhibit the secretion of fusic acid by F.oxysporum.Sixth,after using P.polymyxa YF to face-to-face culture of F.oxysporum,the expression of genes related to toxin production of F.oxysporum was detected,and it was found that the expression of genes FPD1,SIX8,SNF1,and PL1 was significantly down-regulated.The expression results show that the P.polymyxa has a significant attenuating effect on the pathogenicity of F.oxysporum.