Undergraduate Thesis Or Project
 

Relative heat sensitivities and the potential for soil solarization to remediate nursery beds infested with Phytophthora spp.

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  • Infestations of container nursery beds by Phytophthora spp. can be persistent and costly. One method of disinfestation that does not require the use of chemicals is soil solarization, which captures energy from the sun to heat soil and thermally inactivate target pathogens. In laboratory temperature gradient experiments, I investigated the thermal sensitivities of P. ramorum, P. pini, P. chlamydospora, and P. gonapodyides by subjecting inoculum samples to temperatures ranging from 30 – 40°C. Field trials of soil solarization were conducted in July and August 2014 in San Rafael, California and Corvallis, Oregon. Leaf inoculum was buried at 0, 5, and 15 cm in California and Oregon solarization field trials. P. pini and P. chlamydospora were tested in both locations, however due to quarantine restrictions P. ramorum was only included in the California field experiment. In laboratory experiments estimated what temperature treatment would be effective in eradicating 99.9% of samples (LD₉₉.₉) which varied by species and inoculum type. With trials utilizing filter paper inoculum, P. gonapodyides was the most resilient to heat, with an estimated LD₉₉.₉ of 42.55°C. Trials in which rhododendron leaves served as an inoculum, P. chalmydospora was the most resilient to heat, with an estimated LD₉₉.₉ of 47.66°C. Solarization for 2 or 4 weeks eliminated recovery of Phytophthora spp. from all depths in both locations, with the exception of P. chlamydospora at 15 cm in California, which was recovered during sampling at 2 and 4 weeks in this location. Estimated heat tolerances of the four Phytophthora spp. were different from one another, however because of the inconsistencies between trials and inoculum type it remains unclear which species are truly the most heat tolerant. Results from field trials of soil solarization indicate that this is a promising treatment for nursery beds in both Oregon and California infested with Phytophthora spp.
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