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Comparison of Techniques to Sample Xanthomonas axonopodis pv. citri in Windblown Spray

Four techniques were evaluated to sample windblown splash from canker-infected citrus plants. Two volumetric cyclone samplers (PAS450 and Burkard Cyclone) and two passive samplers (funnels and panels) were evaluated. The PAS450 collected no detectable bacteria in any trial. The Burkard cyclone consistently collected spray, but was found to do so even when the power was turned off. Thus, the Burkard cyclone essentially functioned passively, negating the advantage of a volumetric sampler for this application. Panels collected the greatest volume of splash followed by funnel samplers. CFU of Xanthomonas axonopodis pv. citri per ml collected were significantly different between Burkards and panel samplers, but panels and funnels collected similar concentrations (Burkards, funnels, and panels collected 1,182, 1,426, and 2,667 CFU per ml, respectively). Positive correlations were found between the volume and the total X. axonopodis pv. citri collected, and between CFU per ml and total collected for panel and funnel samples. However, there was no correlation between CFU per ml and volume collected for either sampler. The Burkard sample showed a strong positive correlation (P < 0.01) between volume collected, total number of X. axonopodis pv. citri collected, and CFU per ml. The CFU per ml collected by the panels and funnels were similar (coefficient of determination, R² = 0.97), compared with the relationship between the Burkard and panel catches (R² = 0.68), or between the Burkard and funnel catches (R² = 0.62). Panels collected the greatest volume, and effectively collected bacteria-laden windblown splash. The greater sampling area of the panels allowed a more representative sample than the other methods tested.