Biological Control And Mechanism Of Bacillus Licheniformis BL06 Against Pepper Phytophthora Blight (Phytophthora Capsici)

Phytophthora blight of pepper,a worldwide disease caused by Phytophthora capsici,is a destructive soil-borne disease that causes serious economic losses in pepper cultivation and production.Chemical control is a common method to control pepper blight,but the environmental pollution and pesticide residues cannot be ignored.As a sustainable development measure,biological control has broad prospects in the control of Phytophthora blight of pepper.Bacillus licheniformis BL06(NCBI GENBANKK accession number is Bacillus licheniformis HM006898.1)is a biocontrol bacterial preserved in the early laboratory.Previous studies showed that the control effect of BL06 on cucumber downy mildew caused by oomycete disease reached more than 60%.At the same time,the plate antagonism showed good antagonistic effect against P.capsici,Rhizoctonia solani,and other fungi.In this study,strain BL06 was selected as the research material,and the same strain of P.capsici as the oomycete was selected as the research object.The preliminary study on Biocontrol experiment and mechanism of strain BL06 against pepper blight was carried out,which provided a theoretical basis for the industrial application of biocontrol bacteria BL06 to control pepper blight.The biocontrol bacteria BL06 had a stable and obvious antagonistic effect on P.capsici by plate confrontation method.The inhibitory rate reached 75.85%after 6 days of culture.When co-cultured in liquid medium,BL06 could significantly reduce the mycelium growth of P.capsici.The inhibition rates of fresh weight and dry weight of mycelium growth were 77.47%and 77.42%,respectively.The control effect of BL06 on pepper Phytophthora blight was tested.In the experiment of radicle infection,BL06 could significantly reduce the infection rate of P.capsici on the radicle of pepper seeds,and had the ability to protect the pepper seeds from the infection of P.capsici.BL06 could significantly inhibit the infection of P.capsici on the leaves in vitro.The biocontrol effect of strain BL06 on the leaves in vitro was as high as 70%according to the disease index.In pot experiment,BL06 had better colonization ability in pepper rhizosphere;in greenhouse experiment,BL06 had good control effect on pepper blight.The control effect on Pepper blight was 68.74%,52.78%and 47.27%respectively after inoculating pathogenic bacteria for 4,5 and 6 days.Finally,it was found that BL06 could significantly improve the germination rate of pepper seeds.Bacillus licheniformis BL06 had significant inhibitory effects on mycelial growth,sporangium formation,zoospores germination,motility and lysis of zoospores of P.capsici.The increase of mycelial branching after BL06 treatment inhibited the polar growth of mycelia and also caused mycelial dissolution.BL06 significantly inhibited the development of sporangia,and the mature sporangia deformity formed by BL06 treatment.BL06 can significantly inhibit the germination rate of zoospores,and also inhibit the movement of zoospores.In a short time,it can stop the movement of zoospores and disintegrate them.Finally,the effect of BL06 on zoospore infectivity was detected by in vitro leaves,and the growth of zoospores and mycelia was observed under microscope by trypan blue staining at 4,24 and 48 hours after infection.It was found that the zoospores treated with BL06 could not successfully establish infection and could not form disease spots 48 hours after inoculation,which may be due to the fact that BL06 could pass through the host leaf tissue.The infection ability of zoospores was reduced by reducing the germination of zoospores and inhibiting the length of germ tube.