Resistance in western hemlock
Experiments were carried out in Canada to investigate possible resistance of western hemlock (Tsuga heterophylla) to Arceuthobium tsugense (EPPO A1 quarantine organism). It was found that several trees show a high degree of resistance to the dwarf mistletoe and further experiments showed that the resistance of these trees could be repeated in clonal material derived from these trees. The authors assume that the resistance mechanism is operating within, rather than outside, the host branch.
Smith, R.B.; Wass, E.F.; Meagher, M.D. (1993) Evidence of resistance to hemlock dwarf mistletoe (Arceuthobium tsugense) in western hemlock (Tsuga heterophylla) clones.
European Journal on Forest Pathology 23, 163-170.