Hallson Gardens

I was reading a discussion about HVX on another forum... focus on puckering as a symptom. When the idea of using test strips was raised, some fairly cavalier comments were made about innacuracy of the strips - both in missing virus that is there (false negatives) and in indicating virus when it isn't there (false positives.)

I assumed I'd be able to find technical data on Agdia's site or elsewhere on the web giving actual figures - but I'm finding it difficult. I know the Agdia rep back in 2008 said the strips are a 99% match with ELSIA... but Chris said that those are not as accurate as electron microscopy.

So... assuming a plant has reached a reasonable level of virus - do we know what the odds are that a properly used strip will show the plant to be clean even though it is not?

And I'm especially interested in the false positive story. If people believe that perfectly healthy hostas will test positive, resulting in unnecessary destruction, they are going to find it easy to choose not to test.

Do we have good numbers???

I'll throw in my comments and wait for Chris as I'm curious to see what he has to say. I'm not sure at this point I can add anything you don't already know.

However, a properly run test with the strips should be accurate. If you search back you can find the reps comments about comparing 250 tests run in duplicate against the microscope. 2 missed it and 1 of those was user error. If someone is really paranoid, run with two strips. I'm not a big believer in false positives on this one. I think it's more likely to get a false positive when the user is in denial. Not all plants show the symptoms the same way and some may not show them at all.

A false negative is a interesting question. The electron microscope is a nice piece of equipment to have and is very accurate (for $250k it should be). It is possible that a plant with the virus could test negative if there is not enough of the virus present to trigger a positive test with the kits. I don't know where the lower limit kicks in to make a positive result.

I do think if you visually suspect something is wrong with the plant and test it, you should feel fairly confident in the test strips (so long as you ran the test properly). If you get a "negative" and still think something is wrong, run it again with a new strip.

Not sure I helped any, but I'll do a little digging as well for more technical information. Not sure how much is available.

Hi,

I agree with Mike's assessment. False negatives are going to occur when the virus concentration is just too low. Say a batch of Dutch plants was just harvested and they were recently contaminated. The virus could be there, but when you take the strips and test the roots you could very well get a negative since the plants haven't had a chance to actively grow and replicate the virus enough. But if those plants were growing the previous season with the virus there should be enough.

Another scenario is that a plant can be partially virus infected. Always test the most symptomatic leaves to get the most accurate test.

Finally, if a leaf is really showing bad virus symptoms and the HVX test comes up negative, remember it could be a different virus. HVX isn't the only one out there.

thanks, both of you...

Chris - have you seen anything about false positives? I think it could really discourage people from testing if they can use the excuse that they might get a positive even if the plant doesn't have HVX...

Remember just a few years ago when I got attacked pretty heartily by a segment of the hosta posters for suggesting it was irresponsible and wrong to be actively acquiring or marketing virused plants? There was a group who said they liked the look of virused plants and they had every right to buy, sell, and trade the plants.

I haven't seen that craziness for a while, but the current denialists just say stuff like "If you grow hostas, you'll get some virused ones. Just don't worry about it. If one starts to look really bad, toss it and buy a new one. If you are worried about a plant... toss it and replace it. Testing is too expensive... and you can't trust the results, positive or negative anyway... People are just too paranoid - enjoy your plants..."

Or, in the eternal words of Alfred E. Neuman... "Don't Worry - Be Happy!"

I'd kind of like to say something like "There is only a one in a thousand chance of getting a false positive" to add to the statements about the accuracy of the strips.

I heard something once, vaguely, about false positives from an AGDIA rep, but it was something about doing the test wrong somehow. Don't quote me on this, though. It would be a great question for AGDIA.

Yes, there were the original nay-sayers, then the HVX collectors, then the ones who dismissed it as a non-issue. Or those who said it was a conspiracy by the specialty growers to try and get people to stop buying cheap hostas. And the flip side, there were specialty growers who denied the existence of HVX for fear that people would stop buying hostas. While there is still a lot of ignorance about HVX out there, a lot of people have finally come around to a consensus about the fact that the industry is still a wreck and there is still a lot of work to do to get rid of the problem.

Chris_W wrote:I heard something once, vaguely, about false positives from an AGDIA rep, but it was something about doing the test wrong somehow. Don't quote me on this, though. It would be a great question for AGDIA.

Funny you should mention that as a great question for Agdia. I emailed them this morning with that question. Hopefully they'll get back to me. I'll let you know what I hear.

thanks for your replies and for your followup, Steg... if you don't already know for sure, then this is definitely an answer we should get on record from Agdia...

Here is the response I got:

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Hello Mike,

In regards to your question about the HVX ImmunoStrip, we use a very
specific antibody for Hosta virus X with no known cross reactivity or issues
with host reaction. The chance of a false positive is extremely low. The
only instance I could foresee a problem is if too much tissue is used in the
dilution. This can cause what we call a "ghost line" but this will appear as
a green/gray line as opposed to the normal red color. This can be mistaken
as a "false" positive, but this should not be an issue if the test is run
per protocol. Alternately, if the strip is not taken out of the bag after
the maximum 30 minute reaction time, you may see a ghost line develop as
well from material in the sample clogging the membrane.

-----------------

Hello every one. This is Steve from Agdia. Sorry about my long absence. Work and life events make it very difficult to keep up with my online persona. Thank you Mike for posting my response. If anyone ever has any questions, concerns or issues they would like to discuss about the test strips, HVX or other, please feel free to contact. My email is steve@agdia.com or you can call me @ 800-622-4342. If questions pop up on this thread and I haven't chimed in, send me an email and I'll do my best to get it answered ASAP!

Thanks, everyone, for your clarity. I am probably the poster from another forum with the puckered Patriot who noticed tissue breakdown, tested the plant, got a positive result, threw the plant out and then had several forum members suggest that paranoia or panic might have been my problem and that I discarded a perfectly good plant. I never doubted my decision, but I'm really happy for the support I've gotten here.

I understand that everyone is entitled to his or her own opinion on HVX, but I value opinions based on good science more highly than I value those based on emotion. Thanks for the science.