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UBC Theses and Dissertations

Assessment of Colletotrichum gloeosporioides as a biological control of hemlock dwarf mistletoe (Arceuthobium tsugense) Askew, Sue Ellen


Use of an inundative biological control agent, Colletotrichum gloeosporioides, may provide an alternate method to control Arceuthobium tsugense (hemlock dwarf mistletoe) in the coastal forests of British Columbia, especially in variable retention areas, and in riparian and sensitive ecosystems. Variable retention practices can lead to in an increase in hemlock dwarf mistletoe infection, resulting in a loss of tree growth and vigor, reduction in wood quality, and tree death. Five Pacific Forestry Centre (PFC) C. gloeosporioides isolates were screened for conidia production, virulence, and lineal growth rate in culture. Results of this screening and a small field trial revealed that isolate PFC 2415 showed the most promising biological control agent characteristics. The highest number of C. gloeosporioides conidia was produced on the millet substrate compared to rice, slow oats and wheat bran. A field trial using PFC 2415 in three treatments applied in late August 2002 (a Stabileze preparation sprayed on (1) intact mistletoe swellings and (2) on swellings on which all mistletoe shoots had been cut at 0.5 cm, and (3) a sucrose and gelatin preparation sprayed on intact mistletoe swellings) and their respective controls formulated without living inoculum was conducted near Nanaimo, BC. Stabileze® and sucrose-gelatin treatments formulated with C. gloeosporioides reduced the current berry crop by 16 to 36 percent respectively (p<0.05). While the results for shoots appeared promising, heavy background infection and/or secondary infection, especially on controls, limited the ability to detect clear treatment effects. Careful culturing from various live and dead host tissues showed that C. gloeosporioides was unable to invade and kill the mistletoe endophytic system within the living xylem and phloem of the host.

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