The most commonly used techniques in the Test Laboratory are ELISA, PCR, the plating method and bioassays.
ELISA (Enzyme-Linked Immuno Sorbent Assay) is mainly used for testing for viruses. A virus particle is made up of genetic material surrounded by a protective protein mantle. It is an immunochemical reaction and all immunochemical determinations are based on the same principle, the specific bond between antigen and antibody. The ELISA method detects this protein mantle.
The PCR (Polymerase Chain Reaction) testing method detects the genetic code of the organism on which the test is performed (the target). We use this technique on fungi, bacteria and viruses. This sensitive technique is used in various ways. In many cases we use the PCR technique to identify or confirm a suspect organism.
In other applications, the technique is used immediately on the samples to be tested. If the genetic code (target) in question is not found, you will obtain a high degree of certainty that the organism is not present. This technique does not distinguish between living or dead material of the target organism. Therefore, if the result is positive it is necessary to analyse the sample using another test method to determine whether the material is dead or living.
In the plating method we use nutrient media that provide the ideal conditions for growing the organism to be tested. We use this method for fungi and bacteria. Once the organisms have been given sufficient time to develop, the lab technician performs a visual assessment. In many cases we use other techniques such as PCR to confirm the identity of suspect organisms.
In a bioassay we artificially infect suitable host plants with the sap of the material being tested. If the pathogen is present, it produces symptoms on the plant. In this technique, the result is usually visible within 3 to 4 weeks.