Plant invaders as artificial and natural hosts of economically important viruses.

We investigated the role of some invasive species (Abutilon theophrasti, Ambrosia artemisiifolia, Asclepias syriaca, Cyperus esculentus, Phytolacca americana, Solidago gigantea) in the epidemiology of plant viruses. Natural virus infestations have been monitored for more years. Mechanical inoculations and vector transmission studies were also carried out. Even in the last years, a lot of new weed-virus relations have been identified. At low percent (1-2 %) of the collected symptomless samples of A. artemisiifolia, Cucumber mosaic virus (CMV) and Tomato spotted wilt virus (TSWV) were detected. A. syriaca and C. esculentus as natural hosts of four viruses and Brome streak mosaic virus (BrSMV) became known, respectively. Melandrium yellow fleck virus (MYFV) and RS strain of CMV infested P. americana under glasshouse conditions during mechanical inoculations. Neither virological surveys under field conditions nor inoculations in the glasshouse showed A. theophrasti as host of plant viruses. Chlorotic ringspot symptoms on S. gigantea leaves suggested the presence of virus(es), which were not yet identified.