Response of potato cultivars to North American isolates of PVYNTN

Potato cultivars were assessed for their sensitivity to potato tuber necrotic ringspot disease (PTNRD) induced by two North American isolates (Tu619 and Tu660) of the tobacco veinal necrosis strain of potato virus Y (PVY^N) and belonging to the tuber necrosis (PVY^NTN) sub-group. Several widely grown cultivars (e.g. Norchip and Ranger Russet) were found to be highly sensitive to PTNRD, while others (e.g. Russet Burbank, Russet Norkotah and Shepody) were not. The foliage symptoms induced by these isolates were distinct from those reported to be produced by European isolates of PVY^NTN, in that systemic necrotic rings and chlorophyll figures on the leaves were not produced. Instead, the symptoms were similar to those of normal strains of PVY^N. The apparent correlation between resistance to the PVY^O (common) strain group and cultivar sensitivity to PTNRD is discussed.