Bacterium Tapped to Battle Fire Blight Disease in Tree Fruit

Agricultural Research Service (ARS) scientists in Wenatchee, Wash., 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."

ARS is the U.S. Department of Agriculture's chief scientific research agency.