Novel cytopathological structures induced by mixed infection of unrelated plant viruses.

ABSTRACT When two unrelated plant viruses infect a plant simultaneously, synergistic viral interactions often occur resulting in devastating diseases. This study was initiated to examine ultrastructural virus-virus interactions of mixed viral infections. Mixed infections were induced using potyviruses and viruses from other plant virus families. Novel ultrastructural paracrystalline arrays composed of co-infecting viruses, referred to as mixed virus particle aggregates (MVPAs), were noted in the majority of the mixed infections studied. When the flexuous rod-shaped potyvirus particles involved in MVPAs were sectioned transversely, specific geometrical patterns were noted within some doubly infected cells. Although similar geometrical patterns were associated with MVPAs of various virus combinations, unique characteristics within patterns were consistent in each mixed infection virus pair. Centrally located virus particles within some MVPAs appeared swollen (Southern bean mosaic virus mixed with Blackeye cowpea mosaic virus, Cucumber mosaic virus mixed with Blackeye cowpea mosaic virus, and Sunn hemp mosaic virus mixed with Soybean mosaic virus). This ultrastructural study complements molecular studies of mixed infections of plant viruses by adding the additional dimension of visualizing the interactions between the coinfecting viruses.