Ultrastructural and biological aspects of synergistic interactions between unrelated plant viruses

The most devastating synergistic diseases are those in which a potyvirus is one of the co-infecting viruses. Recent studies dealing with the molecular aspects of the potyvirus-involved synergistic diseases demonstrated that the expression of the potyvirus helper component protein is responsible for the synergistic response in mixed infections involving a potyvirus.; Synergistic disease relations became apparent in Arkansas in 1994 with the outbreak of “cowpea stunt” that devastated the cowpea crop in south central Arkansas. This disease, a typical example of a poty/non-potyvirus mixed infection, is caused by the interaction of the two unrelated viruses, Blackeye cowpea mosaic potyvirus (BlCMV) and Cucumber mosaic cucumovirus (CMV). Ultrastructurally, the host cells mixedly-infected with these two viruses demonstrated the presence of characteristic inclusions induced by each virus indicating that a single cell of this host is capable of supporting the replication of two different viruses.; Of biological significance to the mixed infection combinations, the mixed infection involving the beetle transmissible virus of cowpea strain of Southern bean mosaic sobemovirus (CP-SBMV) and the aphid transmissible virus of Blackeye cowpea mosaic potyvirus (BlCMV) was used to determine a possible change in vector specificity. In mixedly-infected cells octagonal MVPAs were noted with the central particle of CP-SBMV encircled by either of the long flexuous rods of BlCMV, raising a question of a change of vector specificity.; In potyvirus involved mixed infections, the potyvirus has been demonstrated to aid the co-infecting non-potyvirus in cell-to-cell movement and in the systemic spread of the con-infecting viruses that are normally localized in the host plant. Studies of a mixed infection of the systemically infecting Peach mild mosaic virus (PMMV) and locally infecting Pokeweed mosaic potyvirus (PoMV) in Chenopodium quinoa were initiated to determine if a non-potyvirus that infects a host systemically could aid in the systemic movement of a potyvirus that normally infects this host locally. The most striking differences between the PMMV singly infected C. quinoa and the PMMV + PoMV mixedly infected C. quinoa were the ultrastructural changes in the PMMV-induced inclusions. (Abstract shortened by UMI.)...