RESISTANCE TO POTATO-VIRUS-A AND POTATO-VIRUS-Y IN POTATO CULTIVARS GROWN IN FINLAND

Phenotypic expression of resistance to potato Y potyvirus (PVY) and po tato A potyvirus (PVA) was tested in 24 potato cultivars and an advanc ed breeding line using graft-inoculation under controlled conditions i n the glasshouse. Resistance phenotypes were determined based on sympt om expression and systemic infection detected with DAS-ELISA. Tubers w ere harvested from the PVA-inoculated plants and tested for PVA with E LISA. Sixteen potato cultivars expressed hypersensitive resistance (HR ) to the strain group Y-0 of PVY. Ute expressed extreme resistance (ER ) to PVY (strain groups Y-0 and Y-N) and PVA, and eight cultivars (Ama zone, Bintje, Fambo, Posmo, Record, Rosamunda, Saturna and Van Gogh) e xpressed ER to PVA. These cultivars produced no PVA-infected tubers (t ubers of Record were not tested). Matilda and Nicola expressed HR to P VA. The tubers of graft-inoculated Matilda produced no PVA-infected sh oots, whereas shoots from Nicola tubers developed necrosis and severe mosaic symptoms and were PVA-infected based on results from ELISA. Com parison with purified PVA antigen (using ELISA) indicated that the sec ondarily infected shoots of the 14 PVA-susceptible cultivars contained 206-804 ng of PVA antigen per gram of leaf tissue.