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Investigations into a biological control strategy for Lodgepole Pine Dwarf Mistletoe Ramsfield, Tod Donald

Abstract

An inundative biological control strategy for lodgepole pine dwarf mistletoe (Arceuthobium americanum) parasitizing lodgepole pine (Pinus contorta var. contorta) in British Columbia was investigated in this study. Of 36 collection sites in British Columbia and Alberta, Caliciopsis arceuthobii was observed at 8 sites and Colletotrichum gloeosporioides was collected from 23 sites and 187 isolates were recovered in culture. It was decided to focus on C. gloeosporioides because it damaged all parts of male and female A. americanum infections, grew readily in culture, produced abundant inoculum in culture and its distribution coincided with the range of A. americanum that was sampled in this study. An isolate of C. gloeosporioides was selected based on growth characteristics and formulated using the 'Stabileze' method for inoculation of A. americanum in a field trial. Two months after inoculation, the average disease rating of A. americanum infections treated with C. gloeosporioides was significantly higher than the controls. One year after inoculation, the average number of fruit present on A. americanum swellings that were treated with C. gloeosporioides was reduced, but the difference between the treatments and controls was not significant. The effect of C. gloeosporioides on the endophytic system of A. americanum was determined through culturing and histopathologic^ examination. Colletotrichum gloeosporioides was cultured from the basal cup region but not from woody tissues. No fungal hyphae were observed within the endophytic tissues of A. americanum; however, two different types of hyphae were observed in the outer dead bark and on the bark surface. Analysis of the distribution of C. gloeosporioides within the canopy of lodgepole pine suggested that the presence of C. gloeosporioides was not related to crown position; under natural conditions, all A. americanum was susceptible to C. gloeosporioides. A5study designed to follow C. arceuthobii infection of A. americanum over time found that the fungus caused an average fruit reduction of 57% each year over the first three years, and a predicted reduction of 39% in the fourth year of the study and that the fungus was able to naturally infect disease free A. americanum. The maximum biocontrol treatment periodicity required for prevention of fruit production was determined to be 3 years, based on the interval between shoot removal and fruit production.

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