Characterization of Phytophthora infestans populations in Cyprus, the southernmost potato-producing European country

Cyprus is the southernmost island country of Europe located in the Mediterranean and despite its limited area, potato production is considered an integral source of the national agricultural revenue. During 2010-2012, a late blight-epidemic period for the country, the population structure of Phytophthora infestans was analyzed via a sample of 539 isolates collected from all the main potato-cultivating regions of Cyprus. We determined mating type, mefenoxam sensitivity, and genetic polymorphism at 12 simple sequence repeat (SSRs) loci. Although both mating types were detected in the country, a gradual -but dynamic- shift towards A2 dominance was manifested over time. The pathogen population also demonstrated reduced sensitivity to the phenylamide fungicide, since 96.2% of the tested isolates had high (70.3%) and intermediate resistance (25.9%) to mefenoxam, suggesting it should be replaced with other active ingredients in local disease management strategies. The genotypic analysis also revealed the predominance of the highly aggressive, mefenoxam-insensitive EU_13_A2 lineage across the country with a frequency of 79.2%. Other samples comprised an older lineage EU_2_A1 (19.5%), a very low proportion of EU_23_A1 (0.37%), and others that did not match any known lineage (0.92%). SSRs data supported triploid genomes among the dominant lineages and patterns of their asexual population history were also apparent. High sub-clonal variation of the 13_A2 population was detected, suggesting introduction events of this widespread genotype to Cyprus from major tuber exporting countries. Present data indicate the severe impact of inoculum migration to the structure of the local population; thus, current phytosanitary procedures should be reconsidered and possibly attuned. This is the first comprehensive study to elucidate the diversity of P. infestans in Cyprus and could serve as a baseline for future monitoring of this highly adaptive plant pathogen since late blight management strategies should be constantly refined according to the traits of the dominant genotypes of P. infestans.