Virus Testing

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I have read the majority of commercial outdoor landscape plant cultivars, and most house plants, are virused. They don't show symptoms. Most landscape and house plants are propagated via meristem or cuttings, with some of annual and perennial herbaceous plants propagated by seed. Mericloning and cuttings/bud grafting are much faster for bringing herbaceous and woody plants, respectively, to market.

Autopsy studies have shown almost all humans have herpes virus permanently in nerve cell bodies in our trigeminal nerve ganglions inside our skulls. That virus is what causes cold sores on the face. If the virus is in nerve cell bodies that innervate the eye, severe corneal damage can occur from cold sores on the eye. On rare occasion herpesvirus can infect the brain, causing severe permanent brain damage or death. Further studies have shown people usually acquire the virus in childhood, probably from kissing adults who are shedding virus though not having cold sores. Many people never get cold sores even though they have the virus in their ganglia. Should we test everybody? Then what?

With proper plant husbandry virus won't be transmitted by the gardener. But bugs can transmit virus when biting a virused plant, then biting a non-virused plant. It is possible to build and maintain bug-proof greenhouses, but it is very expensive. The ongoing rituals needed to prevent introducing bugs are cumbersome.

Commercial tobacco products all contain tobacco mosaic virus. Tobacco mosaic virus can infect orchids. The virus is not reliably neutralized by hand washing. It has been shown people who handle cigarettes can easily transmit this virus to plants they touch. It is likely orchid keepers who smoke have infected most or all of their collection with this virus. Now what?

I'm troubled at the thought of completely losing beautiful old clones of plants that are virused but without symptoms. These plants may be used as pollen parents without transmitting the virus. I have read some commercial growers keep a separate greenhouse for valuable old breeding clones that are virused.

Does it really make sense for a hobbyist to spend a lot of money on virus tests, then discard valuable plants that show no signs of illness?

In theory viruses in orchids might be eliminated if all orchid growers in the world were to test every plant, over a relatively short period of time, then burn infected plants. This would be immensely expensive and will never happen.

Experience with other infections diseases shows testing and elimination will never work. Not even trying to destroy every orchid in cultivation would work. The same viruses that infect our orchids infect many other plants, and they will return.

The isolate and burn approach was tried in the Miami area in the early 2000s to eliminate the newly introduced citrus greening disease. Officials broke into people's gardens and pulled out all citrus trees, symptomatic or not. They went as far as killing one homeowner who tried to prevent the trespass. There was no effect on the spread of the disease, which now is in every citrus producing State in the US.

If commercial growers took effective steps to eliminate completely virus for which testing exists from their stock, and prevent virus from being reintroduced, the price of our hobby would skyrocket, and nobody would be able to afford orchids. The hobby would disappear.

We can only test for a few viruses. It is likely there are many other orchid viruses infecting plants with no signs of disease. This is the situation in other organisms. Every time a new test were introduced growers would have to go through the very expensive process of culling healthy but virused plants again.

I think for the vast majority of hobbyists, testing and destroying virused but otherwise healthy plants isn't necessary. A systematic effort to remove viruses from orchid collections would be impossible. The attempt would inevitably lead to nobody growing orchids.