| Our country is the biggest eggplant producer and consumer globally.However,eggplants are predisposed to pathogen invasion during storage,transportation,and marketing,thus resulting in substantial economic losses.Soft rot caused by Pectobacterium carotovorum is one of the main postharvest diseases of eggplants.Eggplants infected by this pathogen emerge water-borne lesions and gradually become putrescent and malodorous,losing nutritional value.Currently,the primary approach on controlling postharvest diseases of eggplants is through the utilization of chemical bactericide.However,the overuse of chemical bactericide can easily lead to the development of drug resistance of pathogen and environmental pollution,and the residue will pose a threat to the health of consumers.The utilization of antagonistic microorganisms on controlling postharvest diseases of fruits and vegetables embodies security and environmental conservation.Presently,there are few reports on the use of antagonistic bacteria on controlling postharvest diseases of eggplants,especially soft rot,and the involved mechanism is indeterminate.In this study,antagonistic bacterium that have demonstrated effective control against postharvest soft rot of eggplants was screened from the rhizosphere soil of healthy eggplant plants,and the physiological and the molecular mechanisms were explored,so as to offer a theoretical basis for the bio-control of postharvest disease of eggplant and the commercial application of the antagonistic bacterium.The central research findings of paper are as follows:（1）B.velezensis,an antagonistic bacterium with well control efficacy against eggplant soft rot was screened from rhizosphere soil of healthy eggplant plants through in vivo and in vitro tests and identified as Bacillus velezensis.The screened strain of B.velezensis was tested to be practically non-toxic.The control effect of B.velezensis at different concentrations against soft rot of eggplant was investigated.The result indicated that B.velezensis at 1×108CFU/m L and 1×109CFU/m L showed good control efficacy.B.velezensis at 1×108CFU/m L can mitigate the natural decay rate of eggplants with no significant adverse effect on storage quality.（2）In vitro and in vivo results showed that volatile compounds produced by B.velezensis had no inhibitory effect on Pectobacterium carotovorum subsp.carotovorum（Pcc）,which was the pathogen of soft rot.The cell-free filtrate inhibited the growth of Pcc and showed control efficacy against postharharvest soft rot of eggplants.The main antibacterial substance was surfactin,which mainly existed in the extracts by methanol.The yield of surfactin by B.velezensis cultured in eggplant medium for 3 d was 0.244 mg/m L.B.velezensis has the ability of biofilm forming and can colonize rapidly and grow stably in the wounds and on the surface of eggplants.The antagonistic bacterium could increase the activity of resistance-related enzymes and the content of resistant substances in eggplants.It can increase antioxidant enzyme activity,and thus reducing ROS accumulation and MDA content in eggplants.（3）The elucidation of the molecular mechanisms contributing to the heightened state of disease resistance of eggplants by B.velezensis were analyzed based on transcriptome technology.The result showed that there were 193 differentially expressed genes（DEGs）in eggplants treated with B.velezensis,of which 78 were up-regulated and 115 were down-regulated.In light of the functional and pathway analysis results of DEGs,B.velezensis increased the expression levels of genes participating in MAPK,Ca2+and phytohormone（IAA and JA）signal transduction pathways and downstream defense response,genes involved in ROS scavenging,genes involved in synthesis of secondary metabolites（lignin,flavonoids,etc.）,and genes related to cell wall remodeling,thus enhancing disease resistance of eggplants. |
