Plant Diagnostics Applications
PCR can be a tool used in plant breeding programs. For example, instead of screening for insect resistance by scoring infested plants, a breeder can score based on the presence of a marker which is linked to the insect resistance gene. This reduces the chance of environmental effects which could inhibit symptom expression, indicating a plant is resistant, when in reality it is susceptible. In another scenario, PCR can be used
to determine the presence or absence of a transgene in a plant. This is useful in the transformation lab, as well as monitoring gene escape in the field. Figure: Application illustrates how PCR can be used to determine whether or not a particular plant contains the new transgene. Primers complementary to each end of the transgene are developed so only the transgene’s DNA is copied in a PCR reaction. When conducting a PCR experiment, positive and negative controls are used. A positive control is a tube in which it is known that the DNA sequence of interest is present and a band will definitely be produced.
A negative control would be a tube where there is something missing (ie. enzyme, DNA, etc.) so that no bands are expected. For example, if in an experiment no bands are present in the plant samples, but the positive control does show amplification, then it can be concluded those particular plants tested do not have the transgene rather than something going wrong with the laboratory technique.
PCR as a detection test for the presence of a transgene is a very powerful tool. Since only very small tissue samples are needed, the test can be quickly run. Also because PCR amplifies a certain DNA sequence, it can detect the presence of an actual gene, not the gene’s protein product. Therefore, PCR can determine if a plant contains a transgene even if the gene is not being expressed.