Tobacco mosaic virus does infect orchids (Orchidaceae) and one of
the simple diagnostic techniques is to gently abrade the leaves of
a species of Chenopodium (Chenopodiaceae) (sp?) and transfer a small
quanity of fluid from the orchid to the goosefoot and watch for the
infection to display its characteristics on the leaf. I'm pretty
sure that there are several other viruses that cross family lines
to infect orchids, but all my references are at home so I have to
rely on my memory.
John
jford@runet.edu