Virus testing: What does this result mean?

[BrassavolaStars]

Hello all,

I’ve been testing my plants since I found a virus. I tested a blooming cattleya (no color-break) that has strange leaf spots on the older leaves.

I have a red control line and two gray colorless lines that are still visible though as they are slightly grayer than the strip. I assume this counts as a negative? Is that correct? I used older leaves for the sample.

[Roberta]

Originally Posted by BrassavolaStars

Hello all,

I’ve been testing my plants since I found a virus. I tested a blooming cattleya (no color-break) that has strange leaf spots on the older leaves.

I have a red control line and two gray colorless lines that are still visible though as they are slightly grayer than the strip. I assume this counts as a negative? Is that correct? I used older leaves for the sample.

That one is ambiguous. You might want to retest on a newer mature leaf. One of our orchid club members had a couple of tests like this, and after some email back and forth between him, one of the other members, and the manufacturer (Rega) the conclusion was possible positive for a somewhat different virus that does not bind as well to the reagent, or possibly an interference from chlorophyll if the sample was too large. (Those Rega tests are very sensitive, so best not to over-do on sample size) So, marginal. See what it does with a sample from a different area. If still ambiguous, advice from here would be to just handle with care, try to place it so it doesn't drip on other plants, etc. And test again next year.

[BrassavolaStars]

Just did another test. Got similar results. Used a different leaf too. 1cm sample was used.

[Roberta]

Definitely one of those "not definitive" tests. If the plant is healthy and there is no color break indicating a problem, I think any potential for hazard to other plants is very small with normal good care. Do check it again in a year or so to see if there is any change.

Great lessons... you have seen a definite positive (it was loaded), some definite negatives, and a "probably OK but there might be something there, recheck after some elapsed time"

[BrassavolaStars]

Originally Posted by Roberta

Definitely one of those "not definitive" tests. If the plant is healthy and there is no color break indicating a problem, I think any potential for hazard to other plants is very small with normal good care. Do check it again in a year or so to see if there is any change.

Great lessons... you have seen a definite positive (it was loaded), some definite negatives, and a "probably OK but there might be something there, recheck after some elapsed time"

Thank you. That is reassuring.

Here are some pictures of the plant. It happens to be in bloom right now and has been growing well. The only issue is the leaves have odd darker green spots.

[Roberta]

Originally Posted by BrassavolaStars

Thank you. That is reassuring.

Here are some pictures of the plant. It happens to be in bloom right now and has been growing well. The only issue is the leaves have odd darker green spots.

Appearance of the leaves doesn't mean much. Flowers look great. If you want to PM me your email address, I am sure that I can put my hands on the email exchange where this was discussed, and will forward to you.

[katsucats]

With all due respect to Roberta, as I understand it, the color measures a chemical reaction between the antibody and antigen. That means any redness indicates a positive test (reaction activity) as long as the control line is also red. If the control line is faint, then there's a chance the test may not be working properly. In this case, the control line is solid, so if those strips are similar to Agdia strips, I would interpret it as definitively positive for ORSV -- especially since you tested multiple leaves and they remain positive.

The appearance of the leaves and flowers aren't reliable. As an analogy, a person could appear beautiful and healthy and still have HIV.

Edit: I'm assuming those lines are faintly red, as that's how they appear on my monitor. If the line is green, then it may be reacting to chlorophyll. If it's reacting to another similar virus, well, I don't think that bodes well for the plant regardless, whether it has ORSV or some other variant of TMV.

[BrassavolaStars]

Originally Posted by katsucats

With all due respect to Roberta, as I understand it, the color measures a chemical reaction between the antibody and antigen. That means any redness indicates a positive test (reaction activity) as long as the control line is also red. If the control line is faint, then there's a chance the test may not be working properly. In this case, the control line is solid, so if those strips are similar to Agdia strips, I would interpret it as definitively positive for ORSV -- especially since you tested multiple leaves and they remain positive.

The appearance of the leaves and flowers aren't reliable. As an analogy, a person could appear beautiful and healthy and still have HIV.

Edit: I'm assuming those lines are faintly red, as that's how they appear on my monitor. If the line is green, then it may be reacting to chlorophyll. If it's reacting to another similar virus, well, I don't think that bodes well for the plant regardless, whether it has ORSV or some other variant of TMV.

One of the differences between the Rega test and the Agdia test is that the OSRV line and the CymMV lines are reversed. The line you are referring to I believe is actually the CymMV line. It is not really pink. It is more or less tan.

I tried two different tests with different amounts of leaf from different spots and got the same results. I really am not that sure what the deal is.

[katsucats]

Originally Posted by BrassavolaStars

One of the differences between the Rega test and the Agdia test is that the OSRV line and the CymMV lines are reversed. The line you are referring to I believe is actually the CymMV line. It is not really pink. It is more or less tan.

I tried two different tests with different amounts of leaf from different spots and got the same results. I really am not that sure what the deal is.

I can't speak for the Rega test. I know that sometimes chlorophyll or other compounds in the leaf reacts and produces a green or yellow color. Sometimes even a reddish color, although that is rare for orchids. But if there is even a hint of that discrete, clearly delineated red line of the antigen reacting to the conjugate solution (together with the control line), then it is considered positive.

In this case, if it's tan (as in yellowish) with no hint of red, then maybe it's not. A retest with less material and making sure the strip isn't too far into the conjugate may be in order to make sure that there wasn't a red line underneath the yellow/green line.

In either case, my screen obviously needs a color calibration or something. I apologize for sounding the alarm.

[Ray]

The Agdia website list two potential reasons for pale strips - too large of a sample and moisture absorbed if the strips are left exposed to air too long.