Biocontrol of angular leaf spot disease and colonization of cucumber (Cucumis sativus L.) by endophytic bacteria

Endophytic bacteria (EB) isolated from healthy cucumber plant tissues (e.g., root, stem, leaves) were evaluated as possible biological control of Pseudomonas syringae pv. lachrymans, the causative agent of angular leaf spot disease in cucumber. In this study, 24 endophytic bacteria were selected for tests based on biocontrol traits such as indole-3-acetic acid and siderophore production, solubilization of phosphate, and inhibition growth of P. syringae pv. lachrymans in vitro. Some of the selected endophytes successfully inhibited the pathogen were tested in pots. In the pot experiment, two isolates (CB361-80) and (CC372-83) were selected as the most promising biocontrol agents tested against the pathogen. According to the identification carried out by using 16S rRNA primers and sequence analysis, the two selected endophyte isolates (CB361-80) and (CC372-83) showed 99% similarity to Ochrobactrum pseudintermedium and Pantoea agglomerans, respectively. Two EB isolates colonized seeds at the rate of 3 × 10–7.1 × 10 CFU/g 1 day after seed bacterization. The population of the two EB isolates in cucumber tissues were found to be about 2 × 10–7.5 × 10 CFU/g in roots and 3.8 × 10–2.2 × 10 CFU/g in shoots 45 days after seed bacterization. The populations of the two isolates in the root and shoot tissues did not decrease following the inoculation of the pathogenic bacterium. The endophytic strains CB361-80 (Ochrobactrum sp.) and CC372-83 (Pantoea sp.) successfully colonized the cucumber tissues.