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Welcome to the Ralph lab

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Lab photo October 2009

The genus Populus includes poplars, cottonwoods, and aspens, which are keystone species in temperate zone forest ecosystems in the Northern Hemisphere. Poplar is an ecologically dominant and environmentally important species for wildlife habitat (e.g., fire-following aspens), stream stabilization (e.g., riparian cottonwoods) and filtration of agricultural runoff. Poplars are also intensively cultivated in plantation forestry for the production of wood, pulp, and paper. Due to their rapid growth rates, several species in this genus have great economic potential for applications in carbon sequestration, phytoremediation, and as a feedstock for biofuel production. Poplar is a powerful model system for the study of growth, development, and adaptation in woody perennial plants, including the biology of secondary xylem formation, dormancy, adaptation to the environment, and biotic interactions. Poplar is well suited for laboratory studies due to its rapid growth in diverse environmental conditions, diploid inheritance, modest genome size (500 Mb), facile vegetative propagation and genetic transformation, propagation in cell culture, and relatively short reproduction cycle of 7-10 years. Recently, extensive genomic resources have been developed including dense genetic and physical maps, whole-genome microarrays, and a completed 7.5x genome sequence. With its ecological importance, suitability for experimental manipulation, and availability of genomic tools, poplar is a preferred model for studying the response to insect herbivory in long-lived woody perennials.

Quaking Aspen
( Populus tremuloides Michx.)

Photo credit to Terry Spivey, USDA Forest Service,

Poplar 15.5K cDNA microarray
developed by the Treenomix program at the University of British Columbia

Forest insect pests pose a challenge to the sustainability of both natural and planted forests. The risk of forest insect pest epidemics, which cannot be addressed with short-term crop rotation or pesticide application, is increasing with the introduction of exotic pest species and with global climate change. The larvae of several insect herbivores [forest tent caterpillar (Malacosoma disstria), gypsy moth (Lymantria dispar), aspen blotch leafminer (Phyllonorycter tremuloidiella), large aspen tortrix (Choristoneura conflictana)] can cause extensive defoliation to poplar stands, particularly quaking aspen (Populus tremuloides). During outbreaks, trees covering millions of hectares are defoliated, with as many as 20,000 insects/tree. Defoliated trees have reduced photosynthetic capacity and produce less wood, thus reducing the productivity of poplar tree plantations. Although defoliation normally does not kill the tree, repeated attacks increase the incidence of fungal disease and infestation by other insects.

White-marked tussock moth larvae
Orgyia leucostigma
"Choice" assay to evaluate insect feeding preferences

As sedentary organisms, trees cannot avoid or escape biotic (e.g., herbivorous insects and opportunistic pathogens) and abiotic (e.g., drought and temperature) stress in their local environment. Instead, trees have evolved an enormous diversity of anatomical structures and chemical defenses to protect themselves. Trees are a unique biological system in which to study plant-insect interactions as they are long-lived perennial organisms that must be able to mobilize multiple, overlapping defense mechanisms, facilitated by a highly plastic genome, in order to adapt to the changing environment during the lifespan of an individual tree (about 100 years for aspen). The enormous size of trees also allows for the study of spatial considerations in plant-insect interactions.

Populus trichocarpa Nisqually-1 plantlets grown in tissue culture
Poplar leaf total RNA assessed using the BioRad Experion automated electrophoresis system

Research projects in my lab focus on understanding interactions between forest trees and insect pests and consist of laboratory, greenhouse and field work. A broad range of techniques are employed in the lab including microarray transcript profiling, quantitative real-time PCR, biochemical assays for protein characterization, RNA interference to modulate gene expression, and bioassays for insect performance. Students will have an opportunity to conduct research that spans multiple disciplines including plant genomics, molecular biology, biochemistry, forest tree biology and ecology.