16S ribosomal DNA sequencing is the first thing that comes to mind, it is normally used to determine bacterial species. But it can be used on
chloroplastic DNA, as chloroplastic DNA has a bacterial origin. Do you know someone working in a plant biology lab at a university somewhere? They
probably have the primers and the total cost excluding labor would be around 10 euro or so.
Assuming the oil is not highly purified there should be more than enough DNA to do a PCR on. |