Influence of Phytophthora capsici L. inoculation on disease severity, necrosis length, peroxidase and catalase activity, and phenolic content of resistant and susceptible pepper (Capsicum annuum L.) plants

This study explored the level of infection caused by different inoculum concentrations (10(2), 10(3), and 10(4) zoospores mL(-1)) of Phytophthora capsici in 3 pepper cultivars at days 2, 4, and 6. The effect that the infection induced on the peroxidase (POX), catalase (CAT), and phenolics of resistant and sensitive seedlings, as well as the defense mechanism against the pathogen, were also investigated. The resistance of PM-702 against the isolate used was high, whereas KM-Hot and DEM-8 displayed sensitive reactions. As a result of analyses of the leaves and stems from the 3 pepper cultivars, important changes in biochemical parameters were observed between resistant and sensitive cultivars after inoculation with the root rot pathogen R capsici. The maximum increase of POX and CAT was observed in the resistant PM-702 cultivar. However, with a high inoculum concentration (10(4) zoospores mL(-1)), a loss of CAT activity was determined, especially in susceptible cultivars. The maximum increase in phenolics was detected in leaves of susceptible DEM-8 and stems of PM-702 on day 6 following infection. The results suggest that during Phytophthora root rot development there is a relation between the disease induced by R capsici and the antioxidant system.