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Climate Variables and Dothistroma Development: Tools for Future Risk Assessment Braun, Crystal
Abstract: The west central interior has experienced an epidemic caused by dothistroma needle blight (dothi), and the disease is working its way eastward into the central and eastern interior. Previously considered an innocuous disease, dothi has caused mortality of trees in plantations, and mature trees in natural forests. Two main reasons for the increase in disease severity have been proposed. Woods et al. (2005) documented a significant increase in the frequency of warm rain events which they suggest has overcome a weather threshold that limits disease development. Further, until recently, lodgepole pine (the main host for the causal agent in B.C.) was a preferred species for regeneration of harvested areas, and consequently the availability of host increased significantly. The most serious outbreaks of dothi appear to be low elevations and near rivers (Woods and Braun, unpublished data), suggesting that weather in these areas is more conducive to disease development. Observations of dothi indicate considerable variation in the rate of disease development and overall severity, locally and regionally. From work done in the southern hemisphere, where dothi has been causing severe losses in forest plantations for many years, the weather conditions that promote successful infection, colonization of the needle tissue by the fungus, and finally asexual reproduction throughout the summer and early fall, have been documented (Peterson 1966, Gadgil 1974, Karadzic 1989). However, we have very little understanding of the weather conditions that are most conducive to disease development in B.C. where the fungus is thought to be indigenous. In particular, the conditions for, and frequency of, production of the sexual stage of the fungus which is thought to be most important for long-distance dispersal are unknown. Unlike most of the populations in the southern hemisphere, the pathogen in BC has a high level of genetic variability, suggesting that sexual reproduction is common, and that sexually-produced spores are causing new infections, including in remote locations where little forest management has taken place (Dale et al. 2006). The importance of the ascospores in the life cycle of the fungus is unknown at this time. The ascospores may play a role in dispersal during unfavorable environmental conditions. Evans (1984) collected samples from Central America in which earlier collections were composed of primarily the teleomorph and later collections were composed of primarily the anamorph. The ascospores are also produced for a shorter period during the summer months, while the conidia are produced over a longer period both prior to and following the period of production for ascospores (Funk and Parker, 1966, Karadzic, 1989) indicating a possible adaptation to temperature. However the frequency of sexual reproduction, and the mechanisms of long-distance dispersal are unknown. Welsh et al. (2006) demonstrated that outbreaks of doth occurred as far back as the early 1800s, and that the current outbreak severity is unprecedented. In the Interior Cedar Hemlock zone of the Northern Interior Forest Region, lodgepole pine has been removed from the preferred species list as a result of dothi. In these areas, lodgepole pine is limited to 20% of the established species composition. However, in the wake of the mountain pine beetle epidemic, lodgepole pine will be a preferred species for regeneration in much of the area salvaged following beetle attack, particularly across the interior plateau where lodgepole pine dominates. In order to determine the potential risk from dothi, it is necessary to understand the linkage between weather conditions and disease development. This information can then be used in climate models to assess the risk of disease outbreak, and to identify areas where pine should be used minimally in reforestation. This proposal has evolved from observations made during two other studies on dothistroma. In one study (FSP Y0732 ...
Braun, Crystal, Lewis, Kathy J.; Woods, Alex J.. 2008. Climate Variables and Dothistroma Development: Tools for Future Risk Assessment. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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