The effect of Cuminum cyminum, acidity, temperature and inoculum's level on the growth of Xanthomonas campestris

The Xanthomonas genus is one of the most important groups of plant pathogenic bacteria that cause post-harvest spoilage. Substantial crop losses may result from the rapid spread of the bacteria under favorable conditions, lack of seed germination, seedling death and vascular obstruction of plant. The aim of this study was to investigate the combined effects of different concentrations of Cuminum cyminum essential oil (EO; including 0, 0.2, 0.4 and 0.8%), three levels of acidity (5, 6 and 7), two inoculums’ level (103 and 105 CFU/ml) and two incubation temperatures (26 and 28˚C) on the growth of X. campestris in the nutrient broth medium in a completely randomized design with three replications. Growth was monitored by visible turbidity during a 30-day period. The minimum inhibitory concentration and minimum bactericidal concentration of EO against X. campestris was 1 and 2% respectively. According to the results, P-cuminaldehyde was the main component, with a content of 30.5%. The statistical analysis of data showed that the maximum time to detection of bacteria (19 days) in the concentrations of 0.8% EO, pH of 5, the inoculum level of 103 CFU/ml and incubation temperature of 26˚C and the minimum time to detection (16 hours) in the inoculums level of 105 CFU/ml, pH of 7, 28 ˚C and no EO was observed. In addition to the concentration of Cuminum cyminum EO as an antimicrobial agent, acidity of medium is also considered the factors influencing the growth of X. campestris. By decreasing the pH, the time-to-detection of bacteria was increased. In conclusion, using a combination of different factors can inhibit the growth of bacteria, significantly.