Strain Identification and Cross-Protection of Potato Virus Y Affecting Tobacco in Chile

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Abstract
Necrosis severa, caused by potato virus Y (PVY), severely affects flue-cured, burley, and oriental tobaccos in Chile. PVY populations consisted of necrotic and nonnecrotic strains distinguished on the basis of the symptoms produced. Most Chilean isolates were identified as race I (MsMr) or race 3 (NsNr). However, a few were identified as race 2 (MsNr) on the basis of reactions they induced on tobacco cultivars susceptible and resistant to the root-knot nematode. PVY isolates were also distinguishable by their reactions on tobacco Virgin A Mutant, a noncompatible (apparently immune) reaction or compatible reactions that were either necrotic or nonnecrotic symptoms incited on veins or stems. The presence of necrosis did not necessarily appear to be associated with symptom severity. Most nonnecrotic PVY isolates exerted partial protection against a challenge inoculation with a necrotic strain, demonstrating the ocurrence of this phenomenon among PVY isolates and suggesting cross-protection as a possible mechanism for PVY control. Cross-protection may also play a significant role in the epidemiology of PVY diseases.