Xanthomonas citri pv. citri findings in imported citrus fruit consignments in the Netherlands
Citrus bacterial canker (CBC), caused by Xanthomonas citri pv. citri and pv. aurantifolii, presents a major risk to the Mediterranean citrus producing areas of the European Union (EU). The commercial trade of citrus fruit is recognized as one of the seven significant X. citri pv. citri introduction pathways, however, under the current EU phytosanitary measures the likelihood of introduction of X. citri pv. citri and X. citri pv. aurantifolii in the Mediterranean region with infected fruit is rated unlikely. In order to closely monitor the commercial trade flow of citrus fruit, all imported consignments from outside the EU from 2013-2022 have undergone visual inspection for the presence of CBC symptoms upon entering the Netherlands. Consignments that contained citrus fruits with symptoms that could indicate a X. citri pv citri or X. citri pv. aurantifolii infection were quarantined and a sample of symptomatic fruits per consignment was sent to the laboratory for official analysis. The number of consignments containing such symptomatic citrus fruits increased from only 8 in 2013 to 136 in 2022. Survey results revealed the presence of only X. citri pv. citri in 97 infected consignments in the period 2013-2022. Remarkably, 48 consignments were infected with X. citri pv. citri in 2022 alone, representing a 35.3% of the consignments containing symptomatic citrus fruit, matching the expected CBC symptoms. These X. citri pv. citri infected consignments in the period 2013-2022 primarily referred to fruits of C. latifolia (64), C. hystrix (17) and C. grandis (11) and from several countries in South and Southeast Asia as well as in South America. The increasing number of intercepted consignments containing symptomatic citrus fruits due to the presence of viable and highly pathogenic X citri pv citri strains entering the Netherlands raises concerns about the effectiveness of the post-harvest chemical disinfection treatment implemented in the citrus fruit exporting countries. It additionally puts the role of citrus fruit in the long distance dispersal of X. citri pv. citri under debate. Appropriate monitoring of the citrus fruit trade flow by visual inspections for the presence of CBC symptoms and subsequent laboratory testing remains a significant tool in reducing the potential risk of the long distance dispersal of X. citri pv. citri.