Interpreting rega bio test strips

[katsucats]

I usually use Agdia strips but with prices increasing I decided to try importing some Rega Bio tests from Taiwan. I used the last remaining Agdia strip I had to test a couple Laelia anceps divisions I had bought from Tim Culbertson, whose ad said the plants tested negative before shipping out. The Agdia strips returned negative, so far so good.

Now with these Rega Bio strips, it seems that no matter which plants I test, I can see faint red lines barely visible, so I can't tell what counts as positive and what doesn't. I've attached two pictures, one of the test strip under bright LED lights and my phone's flash, and you could hardly see anything in the picture. However, in person if you squint hard enough you could make them out. So in the second pic (with the arrows), I adjusted some color balance settings with my phone and brought the redness out a bit. I've marked where I see the lines, which could be seen in the pictures when zoomed in a lot.

Can anyone help me with this? Supposedly even a faint line means it's positive, but the Agdia strips show negative, and what I want to do next is to test without any plant matter at all and I feel like I would still see the same thing.

[katsucats]

Okay so I did 2 more tests to see how this works. First test, I opened a tube and stuck a strip straight in without any plant matter. After 15 minutes, I took it out and held it under a bright light. I had to look at it really hard to see 2 lines, but they're there. Compared to the anceps sample, the lines are harder to see, but then again it feels like the lines are more visible as the strip dries. On that note, I'll take a picture of the strips tomorrow when all of them are completely dried.

As a second test, I tested a plant I'm 90% sure is virus free, a Cycnoches pendactylon from SVO's most recent release, randomly selected out of the ones I purchased. They've been sitting in a corner opposite a window and haven't "interacted" with the rest of the collection. Same process, took the strip out in around 15 minutes. I still see the lines, a bit more clearer than the "null hypothesis" test and not as clear as the more dried anceps strip.

At this rate unless I see what a definitely positive strip looks like these tests are nearly useless. I'll always be still wondering whether a plant is virused. And if common wisdom is any line means it's virused, then I'd be practically breathing in CymMV from the room air humidity or my entire SVO collection is virused -- both of which I'm sure is not the case.

Edit: Just emailed Regabio with the same information.

[Roberta]

Rega strips are very sensitive. I hope you were using the small sample size that they recommend (or smaller) , or you may get false positives. Excess chlorophyll can definitely do that.

[katsucats]

Originally Posted by Roberta

Rega strips are very sensitive. I hope you were using the small sample size that they recommend (or smaller) , or you may get false positives. Excess chlorophyll can definitely do that.

Thanks. I might have used an excessive sample. The instructions say only a little bruising of the leaf is necessary, but it doesn't say how much is a little. However, that problem aside, I am getting false positives from a non-sample, seemingly suggesting that the tests react with false positives if too much and too little sample is used, leaving only a narrow and unspecified operating zone.

If I don't get a response from Regabio I might have to resell the 45 tests I have left since this is getting too technical for me.

[katsucats]

I don't know if it's possible to see it due to compression when uploading to this site, but here's a photo of the tests side by side completely dried. From left to right, it shows the non-sample test, the Laelia anceps test that might have had too much plant material, and the SVO test. Arguably I could have agitated even the SVO test too much by pushing the stick down 3-4 times.

[Roberta]

You can use a very tiny sample... in this article that describes Kay Klausing's approach for testing a whole collection by taking very small aliquots of multple plants.. if the result is negative they're all clean, one only has to do the individuals if a positive is found.
Virus testing an (entire) orchid collection for CymMV & ORSV: the results at AEO
The author of article used Agdia, but I know that Kay uses Rega - that's where I got mine, he put together a group order in San Diego. The documentation with the kits recommends a sample of no more than 5 mm square. Kay mentioned in one of his talks that smaller size sample works well, so that these are suitable for seedlings and miniatures (so you don't have to destroy the plant testing it). I have found that I can (and should) especially use a smaller sample with Catts, with thick leaves - that 5 mm square of a thick Catt leaf has a LOT of juice. He is also the source of information, obtained from Rega, that too much chlorophyll (from too-large samples) does lead to false positives

---------- Post added at 03:20 PM ---------- Previous post was at 03:12 PM ----------

Originally Posted by katsucats

I don't know if it's possible to see it due to compression when uploading to this site, but here's a photo of the tests side by side completely dried. From left to right, it shows the non-sample test, the Laelia anceps test that might have had too much plant material, and the SVO test. Arguably I could have agitated even the SVO test too much by pushing the stick down 3-4 times.

Easy does it with these tests - sensitivity is very high. For a thin-leaved plant the recommended 5 mm square is OK, for a thick Catt leaf you should use less. Drop the sample in, moosh it a bit with the stick. The buffer should show no more than a little green or cloudiness. If it's very green, sample was probably too big.

[katsucats]

So upon the previous discussion, I decided to take one last test, using a small piece of leaf (as pictured) and only crushing it with the stick once and twisting back and forth once. The sample comes from Carter and Holmes' Phalaenopsis cornu cervi x corningiana, straight out of flask, has to be the lowest risk in terms of virus. Again, it's kind of have to see the lines especially on camera until the strip dries, but I could still see it if I look carefully. I've marked where I see the lines with arrows.

I saw in an older post that said gray lines could be ignored but these lines are never devoid of color. They are red but don't show through the top layer of the strip, which is semi-transparent when it should be white in my opinion. I could prove they're red by putting in in a photo editing app and boosting reds, since it is a bit hard to detect by eye.

So with this I feel like too much chlorophyll can't be the issue. It seems like either the tests are defective or they are designed so that the user has to distinguish between a faded red line (negative) and proper red line (positive).

If anyone else has Rega Bio strips, can you please try placing a strip into the test tube with a random non-virused sample and then taking a picture of it under bright light in 15 minutes? I'll Venmo you $5 for the cost. I just want to see if it's just this batch or not.

Edit: I added a picture of the tube. It's not that clear but visually the liquid didn't change color at all, nor was it cloudy. I know that previously with the anceps sample the liquid was cloudy, and the SVO one was a light green.

[estación seca]

More useful would be seeing a true positive test.

[Roberta]

Katsukats, I'll PM you an exchange between a couple of people in our area (Kay and one other) with regard to the ambiguous tests. (Found the email thread) Not sure that it will answer your concerns (gets into a gray area)

[katsucats]

Originally Posted by estación seca

More useful would be seeing a true positive test.

A true positive would be useful, but a true negative would also be. If a true negative doesn't show faint lines, then it means that my test kit is defective. If a true negative still shows faint lines, then it means the design of Rega Bio strips are defective, or its use requires someone to distinguish a faint red line from a less faint red line, making it rather subjective and hard to use.

Since a test without any samples came back "positive" (with faint lines), then the tests are probably invalid. However, if indeed my randomly selected SVO Catasetum and hybrid flask seedling are virused, then I might as well quit orchids, then file a class action against Agdia. I said that in jest since I really don't think that's the case.