Graduate Thesis Or Dissertation
 

Phytophthora ramorum within an Oregon tanoak forest : quantifying inoculum within canopy throughfall vs. soil splash

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zw12z9829

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  • Phytophthora ramorum continues to cause extensive mortality of tanoaks in southwestern Oregon. Rain readily washes inoculum down through the canopy, causing new infections on the lower parts of the tree and neighboring host plants. Although this aspect of dispersal is well understood, the relative importance of infested soil and leaf litter as factors contributing to the spread of disease remain unclear. The primary objectives of this study were: (i) to compare the amount of inoculum washed down through the canopy to that splashed up from soil and litter, and (ii) to detect and quantify inoculum in relation to soil depth. Over the course of the 2014-2015 rainy season, rainwater was collected 8 times and soil sampled 3 times from within the Generally Infested Area in Brookings, Oregon. Rainwater, soil, and litter were subject to both qPCR and traditional baiting methods. P. ramorum was detected by qPCR more frequently in splash-up from the ground surface than from canopy throughfall. P. ramorum was only detected in soil twice via qPCR and was never recovered by baiting. In canopy throughfall water, qPCR also proved to be a more sensitive way to detect the pathogen than baiting with whole rhododendron leaf baits. In the Oregon tanoak forest studied, quantification of Phytophthora ramorum was not possible because inoculum levels were too low and distribution was too uneven for reliable detection with the methods employed.
  • Keywords: real-time PCR, tanoak, inoculum, soil, canopy throughfall, Phytophthora ramorum
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