ARS studying new beneficial fungus

August 02, 2017
Written by Jan Suszkiw, ARS
Phytophthora ramorum (see large circle) can fell mighty oaks and sicken woody ornamental crops. But it’s no match against Trichoderma asperellum, a beneficial fungus (see strands) that infects and kills the pathogen.
Phytophthora ramorum (see large circle) can fell mighty oaks and sicken woody ornamental crops. But it’s no match against Trichoderma asperellum, a beneficial fungus (see strands) that infects and kills the pathogen. Tim Widmer/USDA
August 2, 2017 – A beneficial soil fungus could offer a bio-based 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.

A BIO-BASED ALTERNATIVE

However, T. asperellum could offer a bio-based 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 per cent.

A chemical fungicide achieved similar results, but only temporarily: eight weeks later, the pathogen re-emerged 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 defences 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.

The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $17 of economic impact.

Jan Suszkiw is with the ARS Office of Communications.

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