Isolation and identification of Xanthomonas citri subsp. malvacearum, cotton bacterial blight disease agent and determination of the antibacterial activity of various plant essential oils

Abstract

Cotton is one of the most important industrial crops produced in large areas in Turkey. Cotton bacterial blight disease agent Xanthomonas citri subsp. malvacearum (Syn. Xanthomonas axonopodis pv. malvacearum) is a seed-borne pathogen. Plant essential oils are natural antimicrobial compounds that have the potential to be used as an alternative to chemical control of seed-borne phytopathogens. In this study, the bacterial pathogen X. citri subsp. malvacearum was isolated from cotton plants showing typical disease symptoms during the 2023 growing season in Diyarbakır provinces and the antibacterial effect of essential oils obtained from 11 different medicinal plants (Thymus serpyllum, Origanum syriacum, Thymus syriacus, Origanum onites, Cistus laden, Salvia aramiensis, Laurus nobilis, Hypericum perforatum, Rosmarinus officinalis, Origanum majorana and Thymbra spicata) were determined by disk diffusion method. Bacterial isolates, obtained from cotton plants showing typical disease symptoms, were identified as X. citri subsp. malvacearum by biochemical and pathogenicity tests and also MALDI-TOF analysis. The essential oils used in the study showed antibacterial activity against the bacterial agent by forming an inhibition zone with a diameter of 6.33-46.33 mm in the nutrient media. T. serpyllum and T. spicata (43.33 mm), O. syriacum (43.00 mm), T. syriacus (38.33 mm) and O. onites (37.3 mm), were identified as the most effective essential oils respectively. The essential oils of H. perforatum (9.67 mm), L. nobilis (9.0 mm) and S. aramiensis (6.33 mm) showed relatively lower antibacterial activity against the disease agent. The results showed that essential oils of Thymus spp., Thymbra spp. and Origanum spp. have the potential to be used as an alternative to chemical control against seed-borne bacterial plant pathogens.