Use of antagonistic bacteria against Xanthomonas hortorum pv. vitians causing disease in lettuce

Abstract

Bacterial leaf spot caused by Xanthomonas hortorum pv . vitians ( Xhv ) is a disease that causes significant yield losses in lettuce. This study aimed to isolate Xhv from diseased lettuce plants and investigate the potential of biocontrol of the pathogen with candidate antagonistic bacterial strains. A total of 47 strains were isolated from diseased plant samples, and 9 of them were identified as Xhv using the Microbial Identification System (MIS). 81 strains isolated from healthy tomato and cucumber plants were tested against the pathogen in in vitro conditions and in vivo experiments. Plant growth promotion features such as nitrogen fixation, phosphorus, potassium, and calcium solubilisation, and biocontrol mechanisms such as siderophore, cellulase, chitinase, protease, hydrogen cyanide (HCN), and ACC-deaminase were determined. It was found that 14 of the strains tested against the pathogen showed antibacterial activity in vitro . In the in vitro tests, the largest inhibition zone was measured in Paenibacillus validus MFD 46 (42.0 mm) and Bacillus megaterium MFD 71 (40.6 mm) strains. In the in vivo tests, the highest biocontrol effect was determined in the applications of Bacillus subtilis MFD 7 and MFD 7+MFD 71 combinations. Bacillus sphaericus MFD 45 strains were found to be positive for all plant growth promotion parameters tested. Pantoea agglomerans MFD 8, Pseudomonas fluorescens MFD 27, and Bacillus sphaericus MFD 45 strains were found to have all the biocontrol mechanisms of action investigated. The obtained results showed that the inclusion of the strains with biocontrol activity in the control programmes against Xhv can be used as a method suitable for sustainability in agricultural production.