Because the genetic material of the pathogen is mixed with that of the plant, it is necessary to target only the genetic material to be copied. We do this by adding small pieces of DNA called primers, which stick only to borders of the region of genetic material that should be copied. These primers, then direct the enzyme where to start and end copying. The PCR process uses a series of hot, cold, and warm cycles. Hot cycles split DNA into single strands.
Cold cycles allow the primers to attach.
We use a process called electrophoresis that separates pieces of DNA by size to tell if that piece of DNA is present.