Pathogen survival and epidemiology of bacterial spot of cucurbits caused by Xanthomonas cucurbitae

Abstract Considering the increasing prevalence and seed-borne nature of bacterial leaf spot, the survival and epidemiology of Xanthomonas cucurbitae were investigated. The bacterium survived in buried plant parts and crop debris at depths of 5, 10, and 15 cm as well as in seeds for up to 24 months. To study epidemiology, disease severity, weekly increase in severity, apparent infection rate and area under the disease progress curve (AUDPC) were taken as dependent disease parameters and correlated with independent weather parameters. A temperature range of 25 to 30 °C and relative humidity more than 70 per cent along with high rainfall conditions favoured the rapid spread of the disease. Increase in disease severity exhibited positive and significant correlation with relative humidity as well as rainfall during 2022 and 2023. In multiple regression, coefficients of multiple determination values indicated that minimum and maximum temperature, relative humidity and rainfall could influence increase in disease severity, apparent infection rate and AUDPC upto 76.50, 79.90 and 76.08% in 2022 and 97.56, 74.17 and 89.90% in 2023, respectively. Additionally, stepwise regression analysis showed that weather factors explained 28.4 to 56.2% of the variation in disease-related variables. Among these factors, relative humidity and minimum temperature were the key predictors of disease severity and AUDPC, while rainfall was a major factor contributing to disease increase.