Effect of temperature shock on citrus bacterial canker lesions in relation to Xanthomonas campestris pv. citri

Temperature shocks at low (0 or 5 degrees C) or high (35 or 40 degrees C) were given to detached citrus leaves for 5, 10, 20, 30, and 45 min in a series of experiments conducted in 1993. Relatively more lesions appeared on the detached leaves and fruits of grapefruit cv. Frost Marsh inoculated with Xanthomonas campestris pv. citri strain XC-100 and subjected to 0 and 5 degrees C shock than when leaves of the same cultivar were subjected to 35 and 40 degrees C shock. With the low temperature shock, lesions started to develop within 7 days, while with the high temperature shock leaves started to rot after 15 days. A pre-inoculation low temperature (5 degrees C) shock to leaves and fruits showed significantly higher number of lesions compared to those which developed when a shock of similar duration was given three days after inoculation.