Page Banner

United States Department of Agriculture

Agricultural Research Service

Agricultural Research Service
U.S. Department of Agriculture
ARS News and InformationSearch News and InfoScience for KidsImage GalleryAgricultural Research MagazinePublications and NewslettersNews ArchiveNews and Info homeARS News and Information
Latest news | Subscribe

Mark Mazzola measures trunk diameter of test trees in a greenhouse: Link to photo information
Click image for caption and other photo information.


Beneficial Bacteria Help Thwart Apple Disease

By Jan Suszkiw
August 14, 2002

Instead of chemical fumigants, beneficial bacteria may be called on to fight fungi that cause replant disease, so-named because it strikes young apple trees planted in old orchards.

The Pseudomonas putida bacteria are part of a “bio-rational” approach now being field tested by plant pathologist Mark Mazzola, with the Agricultural Research Service’s Tree Fruit Research Laboratory in Wenatchee, Wash., and David Granatstein, director of Washington State University’s Center for Sustaining Agriculture and Natural Resources at Wenatchee.

In Washington state, where half the U.S. apple crop is grown, replant disease is primarily caused by certain species of Pythium, Rhizoctonia,Cylindrocarpon and Phytophthora fungi. Unchecked, they can diminish a grower’s crop returns by $40,000 per acre over 10 years, an orchard’s average production life.

Marketing demands often force growers to replant old orchards with new varieties sooner than they might like. Fumigating orchards with chemicals like methyl bromide offers a fast, effective way of sterilizing soils before planting time. But methyl bromide is expensive to use, and will be prohibited in 2005.

P. putida bacteria offer an appealing alternative because they often occur naturally around apple roots and secrete antibiotics that check infection by Rhizoctonia fungi. Mazzola, who identified the bacteria, doesn’t apply them, so much as augment their populations in orchards. This is done by planting a cover crop of certain soft white wheat cultivars whose root secretions create a favorable soil environment.

In a 2001 trial with Gala apples, this resulted in fruit yields of about 46 pounds per tree versus 60 pounds where methyl bromide treatments were used. Field tests begun this May may show whether applying dried rapeseed meal after the wheat crop can synergize, or improve, the bacteria’s biocontrol performance.

Apple orchards often harbor many different replant disease fungi. So the Wenatchee researchers are testing other bio-rational approaches as well. These include using various cultural practices--planting trees in drive aisles rather than rows, for example-- fungicides, and hardier apple rootstocks.

ARS, the U.S. Department of Agriculture's main scientific research agency, has patented the beneficial bacteria.

Top|News Staff|Photo Staff

E-mail the web teamPrivacy and other policiesSite mapAbout ARS Information StaffBottom menu

Home | News | Pubs | Magazine | Photos | Sci4Kids | Search
About ARS Info | Site map | Policies | E-mail us

Last Modified: 8/22/2017
Footer Content Back to Top of Page