Research On Inhibitory Mechanism Of Bacillus Subtilis M23 On Diaporthe Citri

In recent years,Diaporthe citri harm is more and more serious,Causeing serious losses to the economic income of fruit farmers,and being affected by the occurrence characteristics of the pathogen,chemical control needs many times of spraying agents,which not only causes serious environmental pollution,but also brings impact on the cost of fruit farmers,and is not in line with the national policy of"zero growth of pesticides".In order to solve this series of problems,The biological control of Diaporthe citri is particularly important.This study was based on a biocontrol bacterium Subtilis M23 obtained from the laboratory that had an inhibitory effect on Diaporthe citri,by comparing the inhibitory effects of gas volatiles,extracellular proteins and lipopeptides produced by Bacillus subtilis M23 on Diaporthe citri pathogen,the best inhibitor of the Diaporthe citri pathogen was selected.The inhibition effect of lipopeptide substances on hyphal growth ATP of Diaporthe citri fungus and spore germination was studied to explore its bacteriostatic mechanism.The findings are as follows:Through the sequencing analysis of the M23 genome of Bacillus subtilis,Bacillus subtilis M23 has a large number of genes on lipid metabolism,metabolism of terpenoids and polyketones,and other genes for biosynthesis of secondary metabolites,indicating that this strain has the potential to synthesize a variety of lipopeptide substances.By comparing the inhibition effects of Bacillus subtilis M23 on Diaporthe citri pathogens such as gas volatile substances,extracellular proteins and lipopeptide substances,the best inhibitor was selected as a lipopeptide substance,and its inhibition rate could reach more than 85%at a concentration of 0.12μg/m L,which had a strong inhibitory effect.The average EC₅₀ value of the lipopeptide substance produced by strain M23 for inhibition hyphae growth of Diaporthe citri is about 0.045μg/m L.The effect of lipopeptide substances on the biological activity of Diaporthe citri pathogen was determined,and the results showed that:Diaporthe citri pathogen conidia germination rate of only 9.1%at a concentration of 0.03μg/m L of lipopeptide substances;Diaporthe citri did not produce conidia after 48 days of growth in a medium with a lipopeptide substance concentration of 0.12μg/m L,the spore-producing capacity was limited;There was a significant decrease in ATP content in the hyphae of Diaporthe citri bacteria at both EC₅₀and 10 times EC₅₀ concentrations.In summary,Bacillus subtilis M23 produces secondary metabolite lipopeptide substances to inhibit the spore germination,hyphal energy generation and spore-producing capacity of Diaporthe citri,prevent it from infecting citrus and mycelium growth obstruction,and then achieve the effect of preventing Diaporthe citri,This study lays a foundation for further study and control of Diaporthe citri and provides a certain theoretical basis for the follow-up study of biological control of citrus disease.