Soil dwelling bacteria that live off wheat roots like
those shown here could soon be adapted to fight root rot diseases, one of the
biggest problems for growers. Click
the image for more information about it.
Bacteria Pitted
Against Fungi to Protect Wheat and Barley
By Jan Suszkiw
January 9, 2013
Soil-dwelling bacteria
that depend on wheat and barley roots for their "room and board"
could soon prove themselves helpful to the plants in return. U.S. Department of Agriculture (USDA) scientists in Pullman, Wash., are investigating the
bacteria's potential to biologically control root-rot fungi that cause crop
yield losses of 10 to 30 percent annually in the U.S. Pacific Northwest and
elsewhere.
The bacteria are members
of the genus Pseudomonas and include 11 strains that stymie
the growth of Pythium and Rhizoctonia fungi,
which cause diseases in wheat and barley crops. The fungi thrive in cool, moist
soils and can reach especially high levels in crop fields where conservation
tillage is practiced to save on fuel costs, avoid soil erosion, and provide
other ecological and environmental benefits.
The two pathogens are
most problematic to seedlings of spring crops that are four to six weeks old,
notes Pat Okubara, a geneticist in the Agricultural Research Service(ARS) Root Disease and Biological Control
Research Unit in Pullman. ARS is
USDA's chief intramural scientific research agency.
Fungicides aren't very
effective, according to Okubara, and there are no resistant wheat or barley
varieties available to growers yet. Rotating wheat with non-host crops is
difficult, too, because of the pathogens' extensive plant-host range.
However, the Pseudomonas bacteria
can secrete powerful enzymes and biochemicals that can keep these fungal rivals
at bay, to the benefit of wheat and other host crops. Some strains of the
bacteria also help plants help themselves by triggering a sort of immune-system
response called "induced systemic response." Other strains produce
hormone-like substances that spur on root and shoot growth in host plants,
helping them overcome fungal damage.
In greenhouse tests
conducted by Okubara and colleagues, use of five of the Pseudomonas strains
diminished the severity of R. solani AG-98 root rot by 30 to
92 percent and P. ultimum by 32 to 56 percent. Two strains
also reduced rot caused by R. oryzae and P. irregulare,
which plague Pacific Northwest wheat and barley crops. Detailed results appear
in the August 2012 issue of Biological Control.
A commercial product
isn't likely for another few years. But the arrival of any new antifungal
weaponry should be welcome news for wheat growers, especially those who've
shied away from direct seeding or other conservation-tillage measures, notes
Okubara.
Read more about this research in the January 2013 issue of Agricultural
Research magazine.