RESISTANCE TO CUCUMBER MOSAIC-VIRUS IN POTATO

Reactions to two subgroup I isolates (Fny-CMV and Pf-CMV) and two subg roup II isolates (A9-CMV and LS-CMV) of cucumber mosaic virus (CMV) we re studied in three non tuber-bearing wild potato species (Solanum spp .) of the series Etuberosa, and in two tuber-bearing interspecific pot ato hybrids and four potato cultivars using graft-inoculation. Three c lasses of phenotypic reactions (susceptible, hypersensitive, extreme r esistance) were observed in the tuber-bearing genotypes. Susceptible g enotypes developed mosaic or severe mosaic with leaf malformation and had high CMV titres. Hypersensitive genotypes developed either top nec rosis or vein necrosis and/or necrotic spots on apical leaves, and had low CMV titres. Extremely resistant genotypes had no symptoms and no CMV was detected. The hybrid 87HW13.7 (S. tuberosum x S. multidissectu m) developed top necrosis specific to infection with Fny-CMV. The hybr id 'A6' (S. demissum x S. tuberosum cv. Aquila) was hypersensitive to all CMV isolates tested. Extreme resistance was not functional against all CMV isolates. Neither hypersensitivity nor extreme resistance wer e related to the CMV subgroup.