The effects of male and female Arceuthobium americanum (lodgepole pine dwarf mistletoe) infection on the relative positioning of vascular bundles, starch distribution, and starch content in Pinus contorta var. latifolia (lodgepole pine) needles

Abstract

The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a dioecious angiosperm that parasitizes conifers in western Canadian forests, causing significant yearly timber loss. A striking consequence of dwarf mistletoe infection is a marked reduction in the size of the needles located distal to the infection. The purpose of this work was to use microscopy, cytochemistry, and biochemical analysis to determine whether this reduction was associated with changes in needle anatomy and (or) starch content. Furthermore, we wanted to investigate whether these potential changes were affected by the gender of the infecting dwarf mistletoe plant. We developed a ratio (R) that evaluated the position of the two vascular bundles relative to the size of the needle, and found that bundles from male-infected trees were positioned significantly closer together than in needles from female-infected or uninfected trees (p < 0.05). Using the periodic acid – Schiff’s (PAS) reaction for cytochemical identification of starch in situ, we determined that needles from uninfected trees had abundant starch grains compared with needles from infected trees; colourimetric analysis for total starch content corroborated our PAS data. This is the first report of this phenomenon in lodgepole pine, and further supports the use of needle characteristics to assess tree health.