virus testing - false positive?

[Jmoney]

Roberta was kind enough to send me a Rega test so I have attached a pic of the original plant that started this thread. Just to summarize, this is a stem prop of a cultivar originally from Taiwan, and sold by a prominent phal vendor here in the USA.

On the left is Agdia, top line is control, middle is ORSV, bottom is CymMV. On the right is Rega, top is control, middle is CymMV, bottom is ORSV. As you can see perfect concordance. Strong CymMV, weak ORSV. (It is a bit hard to see but the ORSV line is present on the Rega).

In my mind, this provides further evidence validating the accuracy of these tests. It has been mentioned to me a couple times that these tests are not accurate (certainly no test is perfect), but without any actual proof as to how false positives are generated, and I have not reached anyone who has firsthand experience with false positives.

Now this result does not completely eliminate the possibliity of a false positive. It was mentioned to me that insecticide, fertilizer, even milk residue may produce a false positive (again without actual proof). That is theoretically possible to me, if somehow a compound is similar enough to the viral antigen that these ELISA tests bind to (mind you, that is two diferent antigens in this case). However that doesn't pass my "sniff test". I have so many positive results in phals, and so few in my dozens of heirloom cattleyas that have been around 30-60 years, and on occasion plants that have been around 100+ years. Do phal growers apply some chemical to their plants that catt growers do not? Is there some chemical in the stem prop process that sticks around to generate these false tests in phals only? Seems a bit dubious to me, since these plants are years beyond the "cloning" process and it's not like they are all testing positive.

So until I find further information to the contrary (and out of curiosity I am still looking), my conclusion is that many phals growers may be careless in their sanitation, and at least in my limited experience, many "high end" phals growers don't give a damn if their customers end up with high priced virused plants. Bad business practice I say. I'll stick to cattleyas from my trusted vendors from now on. (and despite what these two vendors have told me, yes there are growers out there who vouch for their product). If I find any phal growers that have an actual virus assurance I will post here.

[Jmoney]

Krull Smith informed me that they would certify their phals as virus free, although it seems that rarely comes up (as one would hope from most vendors).

Might be interesting to compile a list of known vendors who are willing to guarantee their plants are virus free. By guarantee I mean willing to refund/replace since I would not expect any large grower to test all their plants, just not feasible. I know many reputable ebay vendors are willing to certify...