Pesticide and Environmental Update
Agricultural
Research Service are Fighting Fire with Fire, Sort of
Their fight is against Erwinia amylovora, the bacterium responsible for
fire blight, a costly disease of apples, pears and other tree fruit.
Controls include pruning, cultural practices and spraying infected trees
with antibiotics. Resistance to one antibiotic, streptomycin, has emerged
in fire blight strains of the Pacific Northwest.
Now, as a bio-alternative, ARS plant pathologist Larry Pusey and
colleagues are calling on Pantoea agglomerans strain E325. The
blossom-dwelling bacterium naturally competes with fire blight for space
and nutrients that both need to survive. Unlike its rival, E325 doesn't
cause disease, according to Pusey, who's in the ARS Tree Fruit Research
Laboratory at Wenatchee. There, he showed that spraying E325 onto blossoms
enables the bacterium to crowd out its fire blight rival so the disease is
less able to cause harm.
E325 is a "top pick" from more than a thousand bacteria and
yeasts that Pusey examined for biocontrol potential using a screening
method that involves growing the microbes on detached crab apple blossoms.
In 1999, soon after ARS patented E325, Northwest Agricultural Products,
Inc. (NAP), of Pasco, Wash., entered into a cooperative research and
development agreement with ARS to work with Pusey's lab in commercially
developing the fire blight-fighting strain.
Under the agreement, Pusey helped NAP evaluate a fermentation medium to
mass-produce E325 and formulate it for use. His lab also furnished NAP
with secondary strains of E325 that can survive being used with
antibiotics. Orchard trials Pusey led from 2002 to 2004 identified
effective application rates. Results showed that E325 was 10 to 100 times
better at suppressing the fire blight bacterium than other
earlier-reported biocontrol agents, including Pseudomonas fluorescens
strain A506.
NAP has exclusively licensed ARS' patent (US No. 5,919,446) on E325 and
plans to register the strain with the U.S. Environmental Protection Agency
for use on apples and pears under the product name "Bloomtime
Biological FD."
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