Plant viruses are usually named after the species in which they were initially identified, and the symptoms associated with that virus in that plant. For instance, that doesn’t mean tomatoes are the only species to be affected by Tomato Spotted Wilt Virus, or even the most susceptible, just that the virus was first identified as causing symptoms of spots and wilt in tomatoes. It turns out TSWV infects a wide variety of plant species, and can cause different symptoms in different plants (or no symptoms at all).
Often the disease had a name before the cause was discovered, and sometimes multiple diseases turned out to have the same cause. Dahlia Mosaic was recognized as a disease for a long time before viruses were discovered. Dahlia Stunt used to be considered a separate disease, but it is now recognized as another common symptom of infection by DMV.
Newly identified viruses still typically get named the same way. Impatiens Necrotic Spot Virus used to be considered a variant of Tomato Spotted Wilt Virus, but researchers declared it a separate species, so it got its own name. It was first identified in impatiens, and causes necrotic (dead) spots on the leaves. It turns out to have a wide host range as well, also including dahlias.
I have a self-seeding annual impatiens (I. balfourii) which grows around my dahlias. I had it tested for INSV for several years along with my dahlia samples, and every time it tested negative even when dahlias nearby tested positive. It continues to look healthy, and I am more concerned about it possibly catching INSV from my dahlias than the other way around.
