|
|
 
|
Beneficial bacteria help thwart apple disease (Aug. 15, 2002 -- CropChoice news) -- The following is from a USDA Agricultural Research Service news item.
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 43 pounds per tree versus 56
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. | |
