Cytological responses of susceptible and extremely resistant potato plants to inoculation with potato virus Y

Abstract

Mechanical inoculation of extremely resistant potato plants bearing the Rystogene with potato virus Y (PVY) induced distinct necrotic streaks along the veins of the abaxial surface of the inoculated leaflets. The number of necrotic vein lesions was related to the inoculum concentration. Vein necrosis was also observed after PVY infection of susceptible potato cultivars, but it developed considerably later compared to the incompatible interaction and the growth of these lesions was not limited. Cytological and histological responses to PVY inoculation were essentially the same in susceptible and resistant cultivars. Strong autofluorescence of necrotic reacting cells and callose depositions around the necrotic sites were observed. At the ultrastructural level we detected necrotic cells with a very electron dense cytoplasm or with degenerated cytoplasmic membranes, disrupted organelles and ruptured envelopes. We assume that a hypersensitive response was elicited in incompatible and compatible interactions. However, because of the delay in the induction of the resistance response in the susceptible plant, the virus might be able to spread beyond the necrotic reacting and callose depositing cells thereby establishing a systemic infection.