PCR (polymerase chain reaction)

Agdia has a rapidly expanding list of PCR tests. Some of these tests are designed to detect specific pathogens, such as bacterial blight of geranium (Xcp), whereas other PCR tests detect entire families of viruses (tobamoviruses, carlaviruses, potexviruses, and begomoviruses) or phytoplasmas (formerly known as mycoplasma-like organisms). PCR tests are more sensitive than ELISA tests and are better suited for plant tissue that has lower concentrations of pathogens.

PCR is able to detect a pathogen, the target, by recognizing the presence of its genetic material (DNA or RNA) in a sample. The aim of the polymerase chain reaction is to make many copies of part of the pathogen's genetic material so there is enough to be detected. The PCR process is made possible by an enzyme that can copy DNA. Since most plant viruses contain RNA, we first must make a DNA copy of the RNA. In the case of certain viruses, all bacteria and phytoplasmas, their DNA can be used directly. The detection process begins when small pieces of DNA called primers attach to specific regions of interest on the target. These primers then direct the enzyme where to start and end copying. If the target pathogen is present, PCR will produce a large quantity of the target DNA.

In Real-time PCR, a fluorescent label is released every time a copy of the target DNA is made. This increase in fluorescence is detected by a special reader in "real time", as it occurs.

In conventional PCR, we separate the products of the process in gels using electrophoresis. In this case, we identify the target DNA by its size.