Survey of huanglongbing associated with 'Candidatus Liberibacter' species in Spain: analyses of citrus plants and Trioza erytreae

The disease huanglongbing (HLB), caused by the phloem-limited and psyllid-vectored 'Candidatus Liberibacter' spp., is threatening the Mediterranean citrus industry. The African psyllid (Trioza erytreae) vector of the pathogen was detected in Madeira (Portugal) in 1994 and in the Canary Islands (Spain) in 2002, and its arrival in 2014 in northwest Spain and Portugal along the Atlantic coast instigated a biological alert, and a contingency management plan was developed. Extensive surveys were conducted in Canary Islands from 2009 to 2015 and in the northwest mainland Spain (Galicia) since the first detection of T. erytreae. Symptoms of the psyllid were observed in most sweet orange orchards of five islands in Canary Islands (93% of the inspected plots). In northwest mainland Spain, 65% of the inspected plots up to 2016 showed T. erytreae symptoms. During the surveys, ten leaves / tree from trees showing suspicious symptoms and from symptomless trees, as well as adult psyllids, were collected and analysed by real-time PCR using a universal 'Ca. Liberibacter' spp. kit, according to the EPPO standard. Suspected samples from other surveyed Spanish regions free of the vector were also analysed. The few samples that were positive in the screening test were tested by species-specific real-time PCR protocols, and they did not show amplification. These data confirm that the Spanish citrus industry is currently free of the 'Ca. Liberibacter' spp., but strict measures to prevent the introduction of this pathogen are required as the presence of T. erytreae increases the risk of its dissemination.