Abstract
Citrus canker, caused by the bacterium Xanthomonas citri subsp. citri (Xcc), is one of the most devastating diseases of citrus in Florida, especially for grapefruit, which is highly susceptible to the disease. There has been much interest in chemicals that induce systemic acquired resistance (SAR). Salicylic acid is an endogenous compound known to be part of the SAR mechanism. A strain of bacterial canker was injected into leaves of grapefruit either alone or with salicylic acid (SA) and oxidative metabolism was evaluated over time. We found that Xcc manipulates H2O2 metabolism by suppressing the activity of SOD and increasing the activities of catalase, ascorbate peroxidase, and peroxidase, which collectively lowered the H2O2 concentration. Salicylic acid treatment transiently restored the activities of SOD and APOD, but was not sufficient to restrict Xcc growth in vivo.
