Evaluation of Commercial Potato Cultivars for Resistance to the Tuber Necrotic Strain of Potato Virus Y

The tuber necrotic strain of Potato virus Y (PVYNTN) causes a disease of potatoes with deep or pitted necrotic lesions symptoms on potato tubers. This affects the cosmetic value of tubers, thus influencing all potato market sectors in South Africa, including table-, processing- and seed potatoes. Eight commercial potato cultivars, namely 'Hertha', 'Mondial', 'Up-to-Date', 'Mnandi', 'Buffelfspoort', 'BP1', 'Pentland Dell' and 'Vanderplank' were selected to determine their susceptibility to a tuber necrotic strain of PVY. Ten virus-free minitubers of each of the cultivars were planted in pots and maintained in a greenhouse at 25 degrees C for 16 hours (day cycle) and 15 degrees C for 8 hours (night cycle). Potato plants systemically infected with PVYNTN maintained as in vitro cultures, were used for mechanical inoculation of plantlets. Three and six weeks after inoculation leaf material was tested in duplicate in a double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA) using a PVYN monoclonal antibody. Results suggest that all the cultivars were susceptible to the virus. The cultivars showed different levels of symptom expression, with all the cultivars, except 'Hertha', showing leaf malformation and mottling. 'Hertha' plants showed leaf drop, leaf deformation and spotting, and all the infected plants died at five weeks, at least three weeks earlier than other cultivars. This result does not support information supplied on the Europotato website (www.europotato.org) which states that 'Hertha' expresses high to very high resistance to PVYN. A confirmatory glasshouse trial will be done to confirm these results.