Screening, Identification And Verification Of Biocontrol Bacteria Against Apple Replant Disease

Biocontrol bacteria is an important measure to prevent and control apple continuous cropping obstacles.The experiment collected healthy apple tree roots and surrounding soil from the continuous cropping apple orchard in Xicheng Town,Yantai City,Shandong Province,and screened an apple continuous cropping obstacle biocontrol bacteria from it,and carried out identification and functional analysis on it.The production of bacterial fertilizer verified the effect of preventing and controlling apple continuous cropping obstacles,The results are as follows:1.The experiment used the plate dilution method to separate soil bacteria,Then passed the filter paper method,microbial arabidopsis co-cultivation and functional mediums screen out bacteria with antagonistic,degrading,and growth-promoting functions.Through morphological,physiological,biochemical characteristics,16S rDNA and gyrA sequence analysis,the bacterium was identified as Bacillus velezensis,which is a new biocontrol bacterium with development potential.At present,strain XC1 has been collected by the China General Microbiological Culture Collection Center,with the preservation number CGMCC NO.20057.2.It has been verified in the laboratory that Bacillus velezensis XC1 has multiple functions such as antagonism,growth promotion,degradation,and production of extracellular enzymes.The bacteriostatic rate of this bacterium against Fusarium proliferaturn,F.moniliforme,F.oxysporum and F.solani is72.95%,70.53%,79.83%and 68.20%,Respectively.It has an antagonistic effect.The number of lateral roots of Arabidopsis thaliana inoculated with the bacteria was significantly more than that of the uninoculated control,which was8 times that of the control,which had a growth-promoting effect.After culturing for 5 days,it was determined by high performance liquid chromatography that XC1 had a degradation rate of 67.19%for 2mmol·L^-1Phlorizin.At the same time,the bacteria can produce extracellular enzymes.The diameter of the protease hydrolysis circle is larger than 40 mm,and the cellulase hydrolysis circle is larger than 25 mm,which has strong enzyme production activity.3.The application of XC1 bacterial fertilizer increased the biomass of Malus hupehensis Rehd.seedlings,and both the aboveground and underground parts grew well.In July,August,and September 2019,after the application of XC1 bacterial fertilizer,Compared with the continuous cropping control,the plant height increased by 45.97%,54.76%,39.25%,the ground diameter increased by 35.02%,34.84%,43.75%,and the fresh mass increased by163.31%,121.09%,and 148.88%compared with the continuous cropping control.Compared with the continuous cropping control,the dry mass increased by 169.66%,96.04%,151.82%;the root length increased by 252.93%,222.83%,and 192.93%compared with the continuous cropping control,and the root surface area increased by 270.34%,337.73%,and 326.34 compared with the continuous cropping control.%,the number of root tips increased by 180.04%,137.67%,and 120.58%respectively compared with the continuous cropping control.4.The application of XC1 bacterial fertilizer increased root vitality and root antioxidant enzyme activity of Malus hupehensis Rehd.seedlings,reduced root malondialdehyde content,and was beneficial to increase plant resistance.In July and September 2019,The root respiration rate of seedlings after applying XC1bacterial fertilizer increased by 86.61%and 54.44%respectively compared with the continuous cropping control.The root superoxide dismutase increased by39.11%and 23.38%compared with the continuous cropping control,and the root peroxidase increased by 69.17 compared with the continuous cropping control.Compared with the continuous cropping control,the root catalase increased by 61.47%and 62.22%,and the root malondialdehyde decreased by70.24%and 61.83%compared with the continuous cropping control.5.Application of XC1 bacterial fertilizer increased the chlorophyll content and photosynthetic parameters of Malus hupehensis Rehd.Seedlings.In July and September 2019,The chlorophyll a content of the seedlings after applying the XC1 bacterial fertilizer increased by 38.54%and 37.34%,respectively,compared with the continuous cropping control,the chlorophyll b content increased by 47.74%and 67.80%,and the carotenoid content increased by19.00%compared with the continuous cropping control.17.76%;the net photosynthetic rate increased by 34.55%and 47.76%compared with the continuous cropping control,the intercellular CO2 concentration increased by4.83%and 9.86%compared with the continuous cropping control,and the transpiration rate increased by 29.32%and 23.05%compared with the continuous cropping control.Compared with the continuous cropping control,the degree increased by 29.81%and 24.08%respectively.6.The application of XC1 bacterial fertilizer can optimize the physical and chemical properties of continuous cropping soil,enhance soil enzyme activity,and reduce soil phenolic acid content.The activities of invertase,urease,neutral phosphatase and catalase after applying XC1 bacterial fertilizer increased by57.41%,171.43%,21.15%and 78.95%respectively compared with the continuous cropping control;compared with the continuous cropping control,the soil after applying XC1 bacterial fertilizer The contents of Phlorizin,phloretin,ferulic acid and cinnamic acid were reduced by 53.66%,66.67%,44.16%and 50.00%,respectively.