VIRUS INTERACTIONS IN MIXED INFECTIONS (CAPSICUM ANUUM).

Abstract

Reciprocal interference experiments between Potato virus Y (PVY) and Pepper mottle virus (PeMV) in Capsicum annuum L. 'Tabasco' and 'Special pepper' (a selection of Anaheim chilli peppers), showed suppression of local lesion production in both directions but incomplete suppression of challenge virus replication (incomplete cross protection). However, suppression was reduced by increasing the concentration of the challenge virus. The source of inoculum of the viruses did not have a significant effect on the subsequent interference between the viruses. A direct relationship was established between counts of local lesions and virus particles counted using the electron microscope. Tobacco etch virus (TEV) was transmitted from one Capsicum annuum L. 'Tabasco' plant to another in the same pot within 4 days after infection of the test plant. Transmission probably took place via root grafts, as the necrotic roots of the test plants intertwined with the uninoculated Tabasco plants. Mixed infections of PVY and PeMV resulted in the production of PVY-N, a new strain of PVY. The new strain, which could be recognized by changes in biological and serological properties, was produced only in mixed infections and was stable after six serial transfers in several hosts. Evidence suggests that the development of the new strain is host dependent. Potato Virus Y in mixed infections with PeMV or TEV in C. annuum L. 'Anaheim' did not induce local lesions, systemic necrosis nor death of Special pepper, while PeMV alone induced the death of Tabasco. The behavior of TEV in Tabasco in a mixed infection was temperature dependent, while TEV alone induced wilt and death of Tabasco irrespective of the greenhouse temperature and season of the year.