Survival of Phytophthora species and other pathogens in soilless media components or soil and their eradication with aerated steam

Abstract

Phytophthora ramorum, while thought to be primarily an aerial pathogen, can be introduced into soilless potting media in the nursery industry as sporangia or chlamydospores and be disseminated widely without being detected. Inoculum of this pathogen, both North American (A2) and European (A1) isolates were used to infest potting media components or soil as sporangia or chlamydospores produced in vermiculite culture or in infected rhododendron leaves. Vermiculite chlamydospore/oospore inoculum of P. citricola, P. cactorum, and P. citrophthora were included for comparison. Survival was determined by monthly sampling by baiting (B) or direct plating (DP) on selective medium. Results indicated that P. ramorum can survive in most media components for up to 6 months, whether introduced as sporangia or chlamydospores. Experiments were also conducted to determine the lethal temperature needed to eradicate P. ramorum from infested potting medium or contaminated plastic containers (over a range of 45 to 70ºC for 30 min using aerated steam mixtures). Other soilborne pathogens included for comparison were Pythium irregulare, Thielaviopsis basicola, Cylindrocladium scoparium, and their survival was determined by baiting methods. All pathogens were killed by temperature treatments of 50ºC or greater. These results show that P. ramorum can survive in potting media if introduced as sporangia or chlamydospores, and infested media or contaminated containers can be sanitized by aerated steam treatment.

Parent Publication

• Proceedings of the sudden oak death second science symposium: the state of our knowledge

Citation

Linderman, R.G.; Davis, E.A. 2006. Survival of Phytophthora species and other pathogens in soilless media components or soil and their eradication with aerated steam. In: Frankel, Susan J.; Shea, Patrick J.; and Haverty, Michael I., tech. coords. Proceedings of the sudden oak death second science symposium: the state of our knowledge. Gen. Tech. Rep. PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 299-302