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UBC Theses and Dissertations

Variation in resistance and virulence in the disease interaction between Melampsora rust (M. occidentalis) and black cottonwood (Populus trichocarpa) Hsiang, Tom


Disease severity, as expressed by spore production rate was compared in a test of fourteen clones of black cottonwood (Populus trichocarpa) by ten isolates of Melampsora rust (M. occidentalis), all collected from their natural pathosystem. Spore production rate was measured by average daily production on leaf disks during twice the latent period in days. The overall average uredospore production during the time from inoculation to twice the latent period was 650 spores/disk/day. Latent period ranged from 6 to 12 days with a median at 8 days. Clones as well as isolates differed significantly in their contributions to spore production rates, while there was no indication of specific differential interaction. The lack of qualitative resistance and virulence indicates that qualitative interactions do not play a major role in disease in this natural pathosystem. This finding holds the promise that black cottonwood resistance will not be devastatingly overcome when used in plantations.

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