Preliminary Study On The Biocontrol Effect And Mechanism Of Bacillus Velezensis LJ02 Against Cotton Verticillium Wilt

Cotton verticillium wilt is a soil borne vascular bundle disease,mainly caused by verticillium dahliae and verticillium albo atum.It has a wide host range,multiple transmission routes,strong pathogenicity,rapid differentiation and other characteristics,which seriously affects cotton quality and yield.Bacillus velezensis LJ02 is a soil rhizosphere biocontrol bacterium.Compared with other biocontrol bacteria,it can stably colonize and reproduce in the soil and has a longer persistence.Therefore,it is of great significance to study the biocontrol effect and action mechanism of Bacillus velezensis LJ02 on cotton verticillium wilt for expanding the use of Bacillus velezensis LJ02 and providing new biocontrol bacteria resources for cotton verticillium wilt.In this paper,we tested the antagonism of LJ02 against Verticillium dahlia,and verified the biological control effect of LJ02 and its colonization in cotton plants through indoor pot experiments.By inducing disease resistance through seed soaking,detecting reactive oxygen species in cotton,lignification of stem cell structure,as well as changes in defense enzyme activity and defense related gene expression in cotton,we preliminarily explore the prevention and control mechanism of LJ02 on cotton verticillium wilt The main results are as follows:1.LJ02 has a strong antagonistic effect on Verticillium dahliae VD592.LJ02 can inhibit the growth of Rhododendron dahlia,destroy the mycelium structure,and inhibit the spore germination and spore production of Rhododendron dahliae.2.LJ02 has good biological control effect on cotton verticillium wilt.LJ02 can preferentially occupy the niche in cotton roots,stems,leaves and rhizosphere soil to reduce the infection of pathogens,and also improve the root activity.3.LJ02 can induce immune response in cotton.The cotton seeds soaked in LJ02 fermentation broth can resist the infection of pathogenic bacteria.The root irrigation treatment of LJ02 fermentation broth can induce the outbreak of active oxygen in cotton,thicken the lignification of stem cells,significantly increase the activities of SOD,POD,CAT and PAL defense enzymes in leaves,and up regulate the expression of defense enzyme related genes PPO,POD and PAL in cotton plants.