Viruses

[nemesis]

When I see orchids marked, “Virus Free”, does that mean these plants have been determined to carry no viruses via DNA sample? Can a plant have a virus, not show outward signs of it, but still transmit it? Is his designation only a concern if you are going to breed it. Thanks! I feel like I will always be a newbie...sigh...
Kelly

[Ray]

I would bet the plant tissue has been tested with a consumer-available kit, not through DNA analysis.

Yes, a plant can be infected with a virus and show no signs, and I suspect it can spread it, but remember that transmission is a statistical function - no outward symptoms implies a relatively low virus loading, which suggests a lower chance of spreading, compared to an obviously infected plant in which the viral loading will likely be greater.

[TZ-Someplace]

I suspect most virus were spread from plants that showed no sign in the days of cut flower production for cattleya corsages and dendrobiums for Hawaiian Leis.

[nemesis]

Thank you for the information! Very helpful
.Kelly

[estación seca]

You can probably find out a lot of information on how the test kits work if you do some searching. The useful search information is generally buried after the first 10-20 pages of advertising.

[nhbeek]

When it comes to expensive plants, I certainly appreciate sellers who test for viruses and guarantee their plants are clean. I feel very iffy spending more than $100 on a plant that has a 20% chance of testing positive for virus.

[estación seca]

The problem is we don't have tests for all bad viruses, and a very low level of infection might not yield a positive test. I don't know how sensitive are the tests.

[nhbeek]

Originally Posted by estación seca

The problem is we don't have tests for all bad viruses, and a very low level of infection might not yield a positive test. I don't know how sensitive are the tests.

The tests are $6. As far as I am aware CYMV and ORSV are 95% of the problem. If I am going to drop $250 on a cattleya (which unfortunately have a high incidence of virus) I appreciate knowing that I am not going to have to bin it.

[estación seca]

As far as I am aware CYMV and ORSV are 95% of the problem.

But we don't really know that since we don't test for most other viruses. I'm not arguing against testing. I'm pointing out it doesn't provide that much information.

[Roberta]

The test strips are pretty good at detecting the viruses that they are designed to test for. If you want a more exhaustive list, you can send sample to a laboratory, and they use more sensitive tests that also look for additional viruses. (I think Critter Creek Labs was bought by Agdia, which now offers testing services as well as selling the strips)

It would not be reasonable for a nursery to test every plant for every virus for which tests exist, there are some for which no tests exist, and as ES pointed out, even for those for which tests exist the titre could be low enough to not be detected. So 100% virus free is not possible... testing for the common ones will find most. Life is uncertain, eat dessert first...