Interpreting rega bio test strips

[Roberta]

The strips were never designed to be dried out, or left in the buffer for longer than specified. You may get invalid results if you deviate from the protocol under which the tests were developed. (Which was for the orchid industry, hobbyists are just a "bonus") A positive, actionable test is unambiguous. Eyestrain not required.

[katsucats]

Originally Posted by Roberta

The strips were never designed to be dried out, or left in the buffer for longer than specified. You may get invalid results if you deviate from the protocol under which the tests were developed. (Which was for the orchid industry, hobbyists are just a "bonus") A positive, actionable test is unambiguous. Eyestrain not required.

Thanks. I did use them according to protocol, and I think I'll just have to accept that the lines are always visible. I'll hold them at a distance next time if it's for sure that a positive line is always unambiguous. With Agdia, positive lines can sometimes be faint, but a negative test always has no line.

[katsucats]

Ugh, I had a definitive positive test yesterday testing 2 plant samples together, but when I tested them individually they were both negative. Not having a good time.

[estación seca]

Batch testing might not be a good idea for strips with a narrow range of acceptable sample size. A certain amount of leaf is needed depending on the test sensitivity. Too much may lead to false positives. If the aggregate sample is the size specified for testing but this is composed of multiple individual samples, there might not be enough infected tissue for a positive test if only one plant is infected.

[katsucats]

Originally Posted by estación seca

Batch testing might not be a good idea for strips with a narrow range of acceptable sample size. A certain amount of leaf is needed depending on the test sensitivity. Too much may lead to false positives. If the aggregate sample is the size specified for testing but this is composed of multiple individual samples, there might not be enough infected tissue for a positive test if only one plant is infected.

You might be right, but as long as too much material doesn't lead to false negatives, I think I'll continue to risk the aggregate being a little more than the specified size for economical reasons. (Also since false positives is less damaging than false negatives in my opinion)

[Roberta]

I know you don't believe me but a very small aliquot will still detect virus if it is there. An overall oversize sample leads to false positives.

[katsucats]

Originally Posted by Roberta

I know you don't believe me but a very small aliquot will still detect virus if it is there. An overall oversize sample leads to false positives.

It's not that I don't believe you, but 1) it's actually difficult to cut that small and I don't want to touch the plant besides the samples when I'm doing this, and 2) it's better to be safe than sorry. When my aggregate sample turned positive where the individual ones weren't, the natural conclusion was that it reacted to a larger sample size. So I used larger cuts for several tests, including aggregates. I wasn't able to reproduce that positive. I want to be sure, since these are going outside where I won't necessarily be watering them one by one to avoid contamination. They will likely eventually be going under timed micro irrigation sprinkler heads.

I am getting my tiny cutting technique down, however. It probably doesn't matter how big the sample is as much as how much is agitated so that the juice mixes with the solution, not that Agdia sized samples would even fit into that tube in the first place.

[Jmoney]

Originally Posted by katsucats

Ugh, I had a definitive positive test yesterday testing 2 plant samples together, but when I tested them individually they were both negative. Not having a good time.

I don't have any advice but I can commiserate with you. I batch test using Agdia (on existing plants in my collection, which presumably are negative) and found a couple nasty surprises. It is the devil then trying to test every plant individually in that batch but I have always been able to finally narrow down the offending plant.

I'm sure I have overloaded the test with excess chlorophyll but I have yet to come across a false positive with Agdia. and all of the positives have been very clear. I don't have much experience with Rega, aside from one instance where Roberta was kind enough to send me a Rega test or two (I had a phal vendor claim my Agdia positive was a false positive, and the Rega was completely concordant with Agdia).