Characterization of Pseudomonas syringae strains associated with soybean bacterial blight and in vitro inhibitory effect of oregano and thyme essential oils

Abstract

Pseudomonas savastanoi pv. glycinea is the causative agent of bacterial blight in soybean. Usually, the control of phytopathogenic bacteria is carried out using toxic pesticides for the environment, which generate rapid bacterial resistance. For this reason, it is suggested to do crop rotation and use certified seeds. New natural compounds are being studied as an alternative to avoid these diseases, like essential oils (EO) which have demonstrated antimicrobial activity. This work aimed to study the antimicrobial activity of EO from Origanum vulgare and Thymus vulgaris against Pseudomonas syringae isolated from soybean bacterial blight in the southern area of Córdoba province. In this study, 14 isolates from Coronel Moldes and General Cabrera fields were identified as P. syringae Group I of LOPAT. The strains P. syringae M3-C1 and P. syringae M7-C1 were identified at the species level by housekeeping genes. EO were obtained by hydro-distillation from thyme and oregano plants. The minimum inhibitory concentration (MIC) was carried out by the broth microdilution technique, determining that both EO could inhibit the isolated soybean strains presenting variations in the active concentrations. The bactericidal activity was also assayed (MBC). These EO were also able to inhibit the biofilm formation of the isolates at sub-inhibitory concentrations. These preliminary studies demonstrated the antimicrobial activity of these EO and their potential use as biopesticides; therefore, future studies will be carried out to develop formulations of these compounds.