Interactions between limber pine (Pinus flexilis) and dwarf mistletoe (Arceuthobium cyanocarpum) related to host biochemistry

Background/Question/Methods

Limber pine (Pinus flexilis) is the most common primary host of the dwarf mistletoe Arceuthobium cyanocarpum, which has been associated with high levels of host mortality in this species.  Although little work has been published on chemically-mediated interactions between P. flexilis and A. cyanocarpum, previous research involving other species in the genus Pinus has found associations between host biochemistry and patterns of attack by dwarf mistletoes and other herbivores and parasites.  In light of this, we analyzed biochemical characteristics of attacked and non-attacked P. flexilis individuals to assess possible associations between these features and attack by A. cyanocarpum.   We used gas chromatography-mass spectrometry to quantify monoterpenes, radial diffusion assays to measure tannin levels, and x-ray fluorescence for elemental analyses.

Results/Conclusions

Attacked trees had significantly higher monoterpene concentrations in both phloem and xylem oleoresin compared with non-attacked trees, while total tannin concentrations were significantly higher in the phloem of non-attacked individuals.   In addition, K:Ca ratios were significantly higher in the phloem of attacked trees.  These results suggest the possibility that infection by A. cyanocarpum induces production of monoterpenes in attacked individuals.  Our findings regarding tannin levels are consistent with published work suggesting inhibition of germination by tannins.  Finally, differences in K:Ca may be related to impacts of infection on host stomatal function.