A polymerase chain reaction method for detecting dwarf mistletoe infectionin Douglas-fir and western larch

Early detection and management of dwarf mistletoe (Arceuthobium spp.) is cu rrently limited by the inability to rapidly detect infection during the 2- to 5-year endophyte phase of the parasite. We describe a polymerase chain r eaction (PCR) technique for detecting Arceuthobium douglasii Engelm. and Ar ceuthobium laricis Engelm. in tissues of its hosts, Pseudotsuga menziesii ( Mirb.) France and Larix occidentalis Nutt. DNA was extracted from branches of 15 infected and 15 uninfected P. menziesii. The PCR product amplified by using the Arceuthobium specific primer in the rbcL gene from Arceuthobium template DNA was a fragment of 708 pairs of bases in length. This product w as amplified from all branches that were visibly infected, but the fragment was not generated from any samples known to be uninfected. The PCR product from conifer DNA was a fragment of 385 pairs of bases in length and was no t amplified from pure mistletoe DNA; this was amplified as an internal posi tive control. The primers developed for P. menziesii and A. douglasii also worked on L. occidentalis and A. laricis. This method detected mistletoe DN A in 7 of 29 P. menziesii branches and 3 of 21 L. occidentalis branches tha t did not have external symptoms of infection and are presumed to be the re sult of the endophyte phase. This method provides a useful tool for experim ental applications and for managing the spread of dwarf mistletoe.