“Good-Guy” Fungus to Take on Killer of Oaks and Ornamental Crops

by Jan Suszkiw, USDA Agricultural Research Service

A beneficial soil fungus could offer a biobased approach to battling Phytophthora ramorum, a pathogen that kills oaks, other tree species and woody ornamentals.

BioWorks, Inc. of Victor, New York, is collaborating with Agricultural Research Service (ARS) plant pathologist Tim Widmer to commercially formulate the fungus, Trichoderma asperellum. The species is a mycoparasite, meaning it attacks and kills other fungi, including P. ramorum, a fungus-like pathogen, notes Widmer, with ARS in Fort Detrick, Maryland.

P. ramorum is best known as the culprit behind Sudden Oak Death, a disease of oak and other hardwood trees in coastal forests of California and Oregon. Nursery growers are familiar with a different manifestation of the pathogen called “Ramorum Blight.” This disease afflicts rhododendron, viburnum, camellia and other woody ornamental plants.

Chemical fumigation and soil sterilization are two common methods of keeping nursery stock blight-free—and compliant with federal and state quarantine regulations meant to prevent the pathogen’s spread. However, T. asperellum could offer a biobased alternative to such soil treatments, which are many times costly, dangerous to use and harmful to beneficial soil organisms.

In petri-dish experiments and outdoor trials with potting mix, use of the biocontrol fungus reduced P. ramorum levels by 60 to 100 percent. A chemical fungicide achieved similar results, but only temporarily: eight weeks later, the pathogen reemerged in the potting mix. Widmer suspects the fungicide temporarily halted the growth of the pathogen, but didn’t kill it.

The biocontrol fungus uses a specialized tactic for breaching the defenses of P. ramorum, which it enters to feed, germinate and start the cycle all over again until little or no pathogen remains in the soil.

BioWorks and Widmer aim to capitalize on this “talent” by formulating the fungus into a wettable powder that can be added to nursery soils and potting mixes.

Read more about this research in the August 2017 issue of AgResearch.

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