Incidence of potato virus diseases and their significance for a seed certification program in Lebanon

Potato fields in the two main production areas of Lebanon, the Bekaa and Akkar plains, were surveyed in two growing seasons for viruses and other pathogens of significance for a potato seed certification program. ELISA tests showed that Potato virus Y (PVY) was the predominant virus, followed by Potato virus A (PVA), Potato virus X (PVX), Potato virus M (PVM), Potato virus S (PVS) and Potato leaf roll virus (PLRV). Of 789 samples tested by ELISA during the two growing seasons, 372 samples were infected by one or more viruses. Single, double and multiple infections represented 75.3, 21.2 and 3.5% of all infected samples, respectively. Incidence of viruses was higher on crops from locally produced uncertified seed-potatoes than on crops from imported certified seed-potatoes. In nucleic acid spot hybridization assays, all 109 samples tested for potato spindle tuber viroid were negative. Other important pathogens of quarantine interest, including Clavibacter michiganensis, Ralstonia solanacearum and Synchytrium endobioticum, were not detected