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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #403379
Research Project: Disease Management in Small Fruit and Nursery Crops Based on Knowledge of Pathogen Diversity, Biology, and Environmental Effects

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: Why is Phytophthora so annoying?! A series of preliminary experiments to understand inconsistencies in inoculum production

Author
item Weiland, Gerald

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/18/2023
Publication Date: 11/1/2023
Citation: Weiland, J.E. 2023. Why is Phytophthora so annoying?! A series of preliminary experiments to understand inconsistencies in inoculum production. Phytopathology 113: S3.183.

Interpretive Summary:

Technical Abstract: Periodically, our method for producing Phytophthora inoculum fails to yield the inoculum density required for planned experiments. Our usual procedure is to grow cultures for 6-8 weeks in a dilute V8 juice/vermiculite mixture and then air dry the infested vermiculite for 1-3 days before incorporating it into potting media for inoculations. Recently, we found that drying the inoculum below 80% moisture significantly reduced viability, so we eliminated this step. Even so, we still occasionally fail to get adequate colonization of our vermiculite. Seeking to understand this issue better, we ran a series of preliminary experiments to evaluate how P. plurivora and P. cinnamomi isolates respond to different dilutions of V8 juice (0-20%) and incubation times (4-8 weeks). Increasing the concentration of V8 generally resulted in faster, fuller growth and increased production of chlamydospores (P. cinnamomi) or oospores (P. plurivora) in petri plates, and also corresponded to higher colony counts in infested vermiculite. Colony counts for both species generally increased in infested vermiculite from weeks 4 to 6, after which colony counts crashed. Zoospore production followed a similar trend, with production generally being greatest during weeks 5 and 6, and least in weeks 7 and 8. Although the results suggest that 6-week-old inoculum is ideal, subsequent inoculation studies with this batch of inoculum failed miserably (no plants died). Our next step is to investigate whether different types of potting media influence infection.