Evaluation of a paper by Guarnaccia et al. (2017) on the first report of Phyllosticta citricarpa in Europe

The Plant Health Panel reviewed the paper by Guarnaccia et al. (2017) and compared theirfindingswith previous predictions on the establishment ofPhyllosticta citricarpa. Four species ofPhyllostictawere found by Guarnaccia et al. (2017) in Europe.P. citricarpaandP. capitalensisare well-definedspecies, withP. citricarparecorded for thefirst time in Europe, confirming predictions by Magareyet al. (2015) and EFSA (2008, 2014, 2016) thatP. citricarpacan establish in some European citrus-growing regions. Two new speciesP. paracitricarpaandP. paracapitalensiswere also described, withP. paracitricarpa(found only in Greece) shown to be pathogenic on sweet orange fruits.Genotyping oftheP. citricarpaisolates suggests at least two independent introductions, with the population inPortugal being different from that present in Malta and Italy.P. citricarpaandP. paracitricarpawereisolated only from leaf litter in backyards. However, sinceP. citricarpadoes not infect or colonise deadleaves, the pathogen must have infected the above living leaves in citrus trees nearby. Guarnacciaet al. (2017) considered introduction to be a consequence ofP. citricarpahaving long been present orof illegal movement of planting material. In the Panel’s view, the fruit pathway would be an equally ormore likely origin. The authors did not report how surveys for citrus black spot (CBS) disease werecarried out, therefore their claim that there was no CBS disease even where the pathogen was presentis not supported by the results presented. From previous simulations, the locations where Guarnacciaet al. (2017) foundP. citricarpaorP. paracitricarpawere conducive forP. citricarpaestablishment, withnumber of simulated infection events by pycnidiospores comparable to sites of CBS occurrence outsideEurope. Preliminary surveys by National Plant Protection Organisations (NPPOs) have not confirmed sofar thefindings by Guarnaccia et al. (2017) but monitoring is still ongoing