virus testing - false positive?

[Jmoney]

Roberta, I think I read that article at one point and got the idea of batch testing at that time. Of course I did have more virused plants than I had thought (still a small number though), including even a couple paphs! (I did not call out the vendors on those since they were in my collection for months to years, but there was a clear pattern of positive tests clustering around certain vendors).

[Roberta]

I'm glad that you got to read the article... when Klausing gave talks at a couple of societies that I attend, it wasn't published anywhere. Found it online...

For anybody who is interested, here is the article. I'm glad that someone captured the key information from Klausing's talk.

Virus testing an (entire) orchid collection for CymMV & ORSV: the results at AEO

[Toadwally]

Thanks for sharing the article.

[Jmoney]

so after several days of radio silence I received an update from the vendor. she states I had never specified wanting only virus-free plants, otherwise she would have declined me as a client. she claims that pretty much no nursery would guarantee virus-free phalaenopsis. and of course since I had the plant for 3 weeks before testing (I got busy and didn't test right away, hey that's life), there is no guarantee I didn't mishandle it.

so that's it, basically its buyer beware. I definitely know many (other) vendors who do not vouch for their plants being virus free. However I do know for a fact that many vendors DO guarantee their product, since most of the time when this came up for me in the past the vendor has made it right (this is a rare occurrence).

My mistake is having too high expectations for a $115 stem prop, and having bought nearly 600 bucks worth from this vendor in the past year I would have expected a better response. (That's a little embarrassing for me to post, but I like the new phals). certainly she is cutting out my future business, so seems short-sighted to me. but it's her choice. I will make sure to ask other vendors in the future before purchasing. Lesson learned I guess.

[Fairorchids]

Just found this thread.

I was warned away from the Agdia test kits by two commercial growers, one from the east coast, and the other from the west cost. It is reported to produce both false positives and false negatives.

Apparently it is critical to test exactly the amount of tissue they specify. Further, any chemical residue on the leaf (fertilizer, spray, etc.), can throw it off too.

At this point, I use only the 'other' test kit from Taiwan (which does not require refrigeration). It is not available in the US, so it must be imported (usually in group purchases to bring the cost down).

Lastly, let me comment on virus in general. It is obviously not possible for any nursery to test 10,000+ plants. However, if the nursery practices proper hygiene, it should not be necessary either. I trade with two growers, who test every plant they bring in, and so far I have had no rejects of plants supplied from my own collection & production.

On the other hand, I also buy plants from the production nurseries in Hawaii (received 3 shipments with total 128 plants today). If anything looks suspect, I will test 1 or 2 samples to determine whether I need to discard or not. But, if they look good, I do not.

If I was to test every single plant coming in, then the typical $35 plant would have to be priced at around $65 to cover the cost of the test kit + the time spent on testing it. The market simply won't bear such pricing.

[Louis_W]

Mistakes happen, but the response from that grower?... yikes..

[Jmoney]

Kim, thank you very much for the info. I would never expect a commercial grower to test everything or even most things, just not feasible from a cost standpoint. I was never critical of a grower for sending a plant that turned out to test positive, as these plants were certainly not exhibiting signs of virus.

I just was more hopeful that an expensive plant would come with more commitment from the grower, that's all.

Can I ask if you know who has had issues with false positives? I have now a couple people mention these issues but I would love to ask for firsthand experiences from those who have delved into these matters. From speaking to some cattleya experts I have a lead on a grower in PA who might have had issues; I am planning on asking for more details.

False negatives to me are a different animal altogether. Many state that viruses may not be homogeneous in a plant, so a false negative does not completely rule out a virus. To me that is just inherent in the biology of virus. The false positive is a problem in the test methodology and science.

---------- Post added at 11:31 PM ---------- Previous post was at 11:22 PM ----------

So just to summarize my experiences with phalaenopsis stem props, which are only a small part of my collection. I have purchased 12 stem props over the past 5 years or so.

1. Grower A, the original subject of this thread, grows primarily phals. I have purchased 5 stem props over the past year, and only this recent one tested positive. I find out now about the "buyer beware" policy. This positive test is in a plant originally from Taiwan.

2. Grower B, a very well-known USA grower with multiple genera including phals. I purchased 3 stem props about 3 years ago, and 2 tested positive. This grower immediately refunded me for the 2 positives. These were plants that originated from this grower.

3. Grower C, another primarily phalaenopsis grower. I have purchased 4 stem props over the past 4 years or so. I recently asked about the virus policy and was told "buyer beware", no guarantees. Unfortunately I had just purchased a plant here that tested ORSV strong positive, CymMV weak positive. This is this grower's own cultivar (USA).

So out of 12 stem props I have 4 positives, which is shocking to me. This is a small sample size but still, 33%? Is it just carelessness in the process? Could it truly be false positive results via Agdia? For reference, I have several dozen old-time cattleya divisions from numerous sources in the US. I believe one had tested positive. Is there some phalenopsis specific process that renders a false positive? Thus far I have had no actual "proof" that is the case. Maybe nobody else is out there testing phals? I know virus testing is firmly entrenched, for better or worse, in the cattleya community.

[Roberta]

I have to suspect that SOMEBODY is testing Phals... Rega, in Taiwan, certainly sells more tests to the industry there than to hobbyists in the US.

[Toadwally]

Too many stand-up orchid growers out there for me to tolerate a virus buyer beware outfit.

[Jmoney]

Roberta, I agree someone has to be testing them, but in the hobbyist community I'm wondering how common that is. I mean, the concept of a clone via stem prop is to cater to those who really value a plant as faithful to the original (often awarded or superior) plant as possible, as opposed to a standard "higher production run" mericlone, and the stem props are priced accordingly. If the positivity rate is anywhere near as high as I'm getting then there oughta be a lot more unhappy customers out there!

Toadwally, I agree completely. I never thought I'd have to ask vendors who sell plants in the 75-150+ range whether they will "vouch" for these plants. A cheaper 25 dollar mericlone, well I wouldn't care nearly as much. I guess we all have to make our choices then. I don't know how many people here are into stem props (and also into virus testing) but would think this thread could be highly relevant...