vendor Virus Policies

[Jmoney]

Ray, I agree with you 100% that negative tests on all plants in a collection does not equate to "virus free". It does not factor in the other viruses, and of course false negatives. Perhaps some plants have low level infections that don't cause a positive test line.

However I do not think that the other (human) viruses you mention are necessarily applicable, as VZV (chicken pox) and HIV are well-known for causing chronic infections. In the former, the virus stays dormant in the neurons, and in the latter, we have not yet found a cure, although suppression with antivirals avoids deterioration of the immune system. That is why kids who are vaccinated against VZV should theoretically never get chicken pox / shingles, assuming immunity doesn't wane over time. HCV is a good example of a virus that usually causes chronic infections...and over the past decade or so newer antivirals are capable of actually eradicating this infection.

estacion, tobacco mosaic is the same family of virus as ORSV. I heard that some of the academic plant research facilities had outlawed smoking around the plants back in the day when it was more common to smoke in the greenhouses. I am not sure that anyone has documented spread in this fashion but it seems to be a possibility.

[Roberta]

Originally Posted by estación seca

Does tobacco mosaic virus cause common orchid test strips to react? TMV has been reported to infect many orchids. Do orchid retailers prevent smokers from entering? All smoking tobacco, and the hands of smokers, contain infective TMV. Host plants for TMV are ubiquitous in temperate zones and anywhere people garden. Jimson weed (Datura) species are ubiquitous in temperate zones.

I think that TMV does cause test strips to react - it's closely related to CymMV . And also capable of infecting orchids. Humans are definitely vectors. Another reason for not smoking!

[Leafmite]

Viruses mutate because they do not replicate accurately and they pick up pieces of DNA from here and there.

Variations of mosaic virus infect many different plants. Figs, Passionfruit, tomatoes, corn, etc. Many plants have been selected for resistance so, while they might carry the virus, they will not exhibit symptoms and will still produce a yield. If your neighbor grows hosta, there are many that are infected with virus. Tulips that were virused were sold for a while as they had 'interesting' blooms. The list goes on....

Many plant vendors do not allow people to visit their greenhouses because they do not want diseases introduced to their plants. As ES mentioned, someone who smokes might carry mosaic virus on their hands and spread it. I recently bought some citrus trees from a vendor who does not allow visitors as they want to protect their stock.

Many plants have been selected to become resistant to different viruses. Many years ago, there were plants that had no resistance to virus and would exhibit the symptoms quite rapidly. People used these indicator plants to test for virus (make a cut in the stem of the indicator plant, introduce sap from the plant you want to test and wait to see if the plant remains healthy or shows symptoms). It was a cheap way to test plants for virus. I read about fifteen years ago that these plants are now all resistant to virus and no longer show symptoms.

[minicoerulea]

Originally Posted by Ray

I may be totally wrong about this, but I think it's a bit naive to think one's collection is virus-free.

This sounds like a reply to my post, so I'll point out that I did not claim that anyone's collection was virus free.

Originally Posted by Roberta

I think that TMV does cause test strips to react - it's closely related to CymMV . And also capable of infecting orchids. Humans are definitely vectors. Another reason for not smoking!

The Agdia CymMV/ORSV strips do not detect TMV, per their validation report.

Originally Posted by Leafmite

Many plants have been selected to become resistant to different viruses.

Yes, that's another reason to test for what we can -- since native orchids aren't likely resistant to imported pathogens.

[katsucats]

Originally Posted by Ray

I may be totally wrong about this, but I think it's a bit naive to think one's collection is virus-free.

Passing a test means the viral loading was below the detection limits of the test, not that there are no viruses present. Sort of like the HIV med ads that claim they keep you "undetectable".

I am a firm believer that plants carry every virus to which they have ever been exposed, but - just like us - if we are kept otherwise healthy, thew don't rear their ugly heads.

If you had chicken pox, you are carrying the Varicella zoster virus, but may never get shingles (good for you if you don't), while others do. In retrospect, it seems likely that my body fighting the early stages of cancer made my immune system unable to keep shingles at bay.

I'm no biologist, but I do know that plants lack immune systems that animals have. Specifically, they don't have lymphocytes or macrophages to identify pathogen genetic signatures, bind to them or create antigens to destroy them. That means that while in a human a virus might infect and not replicate (and die out), replicate and be checked by the immune system, or replicate and progressively increase viral load, in plants they either fail to replicate and remain a local infection, or become systemic and increase viral load. I can't find any mechanism that would allow plants to innately suppress systemic viral load once infection takes hold. In a human, being in good health improves immune system function. Plants don't have immune systems.

Therefore, I can only conclude that if a test shows false negative, it would only be because the orchid was recently infected. But test strips can detect a sample with up to 1:583,000 dilution. So it is in my opinion extremely unlikely that a test would just continue to fail to detect a virus.

It is extremely unlikely for an HIV test to continue to fail to detect viral load if the person isn't successfully fighting off the virus due to a rare genetic mutation (i.e. that changes his genetic signature so that the immune system could recognize HIV from itself) or anti-retrovirals. Nor a Covid test or pregnancy test, etc. The HIV false negative rate is less than 0.01% once enough days has elapsed to ramp up viral load (30-40 days).

I agree that testing negative (plants) does not mean that the plant is necessarily free of virus. But testing plants greatly reduces the chance of unknowingly having a positive plant. I'd disagree if you were implying that the effect wouldn't be significant because "plants carry every virus to which they have ever been exposed" at a low level.

Even humans don't carry every virus we've been exposed to. We carry signatures of viruses so that the immune system could detect pathogens. Viruses only remain in low viral load if our immune systems are working, or with external help in the same way that we could reduce plant viral load with actinobacteria or other latent viruses, but test strips have enough sensitivity to detect even reduced viral loads.

---------- Post added at 07:19 PM ---------- Previous post was at 07:10 PM ----------

Originally Posted by Leafmite

Many plants have been selected to become resistant to different viruses. Many years ago, there were plants that had no resistance to virus and would exhibit the symptoms quite rapidly. People used these indicator plants to test for virus (make a cut in the stem of the indicator plant, introduce sap from the plant you want to test and wait to see if the plant remains healthy or shows symptoms). It was a cheap way to test plants for virus. I read about fifteen years ago that these plants are now all resistant to virus and no longer show symptoms.

As far as I know, indicator plants rapidly show infection, then segments them so that the infection remains local.

For many plants it may be possible for certain species to be naturally resistant to some pathogens. But for orchids each breeding generation takes 5-10 years, so it would be highly unlikely that any such breeding has occurred to make orchids resistant to viruses. CymMV was discovered in 1950, and no one took it seriously until the 2000s. By the mid-90s, depending on the market, between 25% to 70% of plants were virused.

[Dalachin]

Hi all, thanks for starting this thread, I am watching it with interest. I also virus test new plants and discard or give away any new infected ones. I have a relatively young collection and it seems counter-productive to add known damaging pathogens to my growing areas.

I don't have a lot of disposable income or time, so I do try to buy plants from known vendors that have good reputations or policies. I've found it very frustrating to have conversations with vendors about their virus policies. I can add the following results from my conversations:

H and R Nurseries-- no guarantees but they are likely to replace the plant since they would do that anyway with a damaged plant.

Diamond Orchids-- "no guarantees"

I've actually stopped trying to ask vendors in advance... it's too frustrating. It seems that many will "do the right thing" when they encounter an unhappy customer. Also, the virused plants that I've encountered have likely been divisions rather than seedlings, so I am more wary of these.

I have a very hard time understanding how professional growers can lend a blind eye to a known pathogen that has been proven in numerous studies to have detrimental effects to plants. Even if individual plants are healthy, what happens as they age and encounter new stresses? Also, even if one plant is "resistant" to the virus, other plants in a collection are unlikely to be resistant.

I also believe that if more consumers cared and showed that they cared, growers might give more care to preventing further propagation and spreading of viruses.

[isurus79]

Following

[nhbeek]

Most vendors that aren't known bad actors will begrudgingly refund or replace virused plants.

Aside from a handful that actually care about virus (hint the word virus appears somewhere in their literature), most regard it as a customer service problem, and not a real problem. Hence the attitude that you are a Karen and they just want you to shut up and go away.

Most customers dont test and don't discover virus unless the plant gets mosaic patterns on it's leaves which is a rare occurrence. If you follow the AOS facebook page, many hobbyists are posting pictures of completly virused flowers thinking it's just a nice splash! So most vendors prefer to ignore the problem, and even vendors who are not know crap regard the complaint as a slap in the face.

At this point I just price in the guestimate chance of virus into the purchase price. Otherwise I am buying something I have a 50% chance of returning, at which point its just ridiculous.

[alecStewart1]

Originally Posted by Leafmite

Many plant vendors do not allow people to visit their greenhouses because they do not want diseases introduced to their plants. As ES mentioned, someone who smokes might carry mosaic virus on their hands and spread it.

Hmm, interesting. So is that why it's not necessarily wrong to be cautious about plants being shipped internationally, as smoking is more common outside of the US in certain areas of the world? Say certain parts of Asia? And therefore purchasing a phytosanitary certificate is required?

[Ray]

Originally Posted by alecStewart1

Hmm, interesting. So is that why it's not necessarily wrong to be cautious about plants being shipped internationally, as smoking is more common outside of the US in certain areas of the world? Say certain parts of Asia? And therefore purchasing a phytosanitary certificate is required?

A phytosanitary certificate is required for bulk imports, but to the best of my knowledge, viruses are not part of the pathogens included. They tend to be referring to known, general health, rather than individual diseases.