Pocket tips: sample selection
Pocket Diagnostic tests are easy to use. However, attention to detail is vital. If this is overlooked, the test may not perform as well as it should. This regular feature will provide hints on how to get the best out of your tests. We’ll cover everything from sample selection and preparation to running the test.
Running the Pocket Diagnostic test is only part of the procedure; sample selection is the key to achieving a reliable result. Three important points to remember are:
1. Take symptomatic material only
In most cases, the Pocket Diagnostic test will detect pathogen only in samples with visible symptoms. If you test plant material without symptoms, the test is unlikely to detect the disease. It is also vital that you do not use dead tissues as the pathogen is unlikely to be detected in dead tissues, even though it is continuing to infect the rest of the plant.
It is much more accurate to sample from the junction between healthy and diseased tissue as the pathogen is growing at its fastest rate here. That way there is a better chance of detecting the pathogen and achieving a reliable result.
Pocket Diagnostic tests can be used on a wide variety of plant materials – wherever the symptoms of disease are found. When selecting and using samples from different plant tissues, the following notes may be helpful:
Leaves – with thick or waxy leaves, cut, crush or tear the sample before adding to the bottle
Stems – for woody tissues, cut the sample finely before adding to the extraction bottle
Roots – if possible, rinse soil or compost off the roots
Fruits – use surface tissues if possible. The soft flesh of ripe fruits will block pores in the test strip membrane
Flowers – no particular problems.
2. Sample from several places
When testing larger plants such as trees, it is important to remember that the pathogen you are trying to detect is unlikely to be distributed evenly throughout the plant. To maximise your chances of detecting the pathogen, take small sub-samples from several areas showing symptoms. Be careful not to overload the sample bottle by using too many sub-samples (see point 3 below).
If you don't want to combine sub-samples from one large plant, you may need to carry out several separate tests on the same plant to maximise the possibility of detecting pathogen.
Pocket Diagnostic tests can be used to screen for pathogen in batches of plants. In this situation, take small samples of tisuse from 3 - 4 plants and combine into one extraction bottle. Again, take care not to overload the sample extraction bottle.
3. Use small tissue samples
It is important that you do not use too much plant tissue as this will prevent the test from working correctly. If too much sample is added to the bottle, the liquid will become too viscous and prevent the test from running properly. If this happens then the important internal components of the test will not be released properly and this may cause unreliable results.
For best results use approximately 0.2g of plant material, this is equivalent to a 25mm square of a typical leaf (such as tomato). See instruction leaflet for guidance.
If you are having any problems using Pocket Diagnostic kits, please contact us and we’ll try to provide help in the next issue.