Antibacterial Efficacy of Clove Essential Oil Against Xanthomonas phaseoli pv. phaseoli and Its Influence on Pathogen Responses in Bean

One of the most significant diseases is the bacterial blight of beans caused by Xanthomonas phaseoli pv. phaseoli. In the present study, different concentrations of clove oil were evaluated on in vitro growth inhibition of X.s phaseoli pv. phaseoli (Xap3), whereas its in vivo effects on disease severity, and bacterial colony-forming units, were investigated. While a considerable inhibition of in vitro growth was seen, the pathogen's growth was significantly inhibited as the concentration was raised. Higher concentrations (10, 12, 14 mu L/mL) effectively inhibited the growth as the growth of 26.6, 27.1, and 28.2 mm, respectively, was recorded. After 4 and 12 days of application, foliar application (1%) of clove oil in the greenhouse showed a significant reduction in disease severity (60% and 50% respectively). After 4 days, the population of colony-forming units on bean leaves was lower (0.5 x 10(6)) and a gradual increase (5.0 x 10(6)) after 16 days was recorded in clove oil-treated plants that were significantly lower than in infected control. A total of 18 chemical compounds including alkaline, alkane, isomer, alcohol, fatty acids acetates, and terpene were found during GC-MS analysis. The main component, eugenol (64.82%), which is an ally chain substituted guaiacol molecule and an efficient scavenger of reactive oxygen radicals responsible for cell proliferation, was detected in a higher amount. These results confer the application of clove oil can provide an alternative to chemical fungicides to mitigate this disease and therefore, future studies should focus on the field application of clove oil.