Extraction methods for Xanthomonas campestris pv. campestris from brassica seed

Two series of seed tests were carried out for the detection of Xanthomonas campestris pv. campestris (Xcc) in 107 Brassica seedlots. Sub-samples of 5,000 or 10,000 seeds were extracted in saline with a centrifugation step after 5 min shaking incubation, followed by stationary incubation or shaking incubation, and plating on semi-selective media (FS and NSCAA or mCS20ABN). The inclusion of a centrifugation step after 5 min incubation of extracts increased the proportion of Xcc positive sub-samples and seedlots. Omission of the centrifugation step was estimated to give a 25% chance of false negative results. Both centrifugation after 5 min and dilution after 2.5 h incubation should be used to minimise the likelihood of false negative results. Numbers of Xcc were similar on FS and NSCAA media, but saprophytes were greater on NSCAA medium. Numbers of Xcc were greater on FS medium than on mCS20ABN. However, two media should be used to minimise the likelihood of false negative results. Greater numbers of both Xcc and saprophytes were detected by shaking than by stationary incubation, but the increase in Xcc was greater than the increase in saprophytes; shaking also resulted in a higher proportion of positive sub-samples/lots. Continuous shaking represents an improved extraction procedure compared to stationary incubation of extracts.