Gray Leaf Spot Double TroubleBy
September 10, 1998
Scientists with the Agricultural
Research Service have discovered a "cousin" of the fungus that
causes gray leaf spot in corn--a finding that could mean double trouble for
growers across the Cornbelt.
The fungus Cercospora zea-maydis causes gray leaf spot. Spores from
the fungus land on corn plant leaves and infect the tissues, opening the way to
other crop- damaging diseases. A severe infestation can reduce corn yields by up
to 25 percent. C. zea-maydis was first observed in southern Illinois in
1925, but since the mid-1980s it has spread across the Cornbelt. Thriving in
warm, humid environments, the fungus can be found as far west as Kansas and
Nebraska in irrigated corn.
Now, a plant pathologist at ARS'
Production and Pest Control Research Laboratory in West Lafayette, Ind., has
found a second type of gray leaf spot fungus in the eastern United States. This
fungal "cousin" causes the same disease symptoms in corn but has
slight genetic differences from the more common type.
The finding could prove crucial as scientists probe the genetic makeup of
the disease to learn more about its virulence. Breeders will have to develop
new varieties resistant to both forms of the gray leaf spot fungus.
Both types of fungus overwinter in crop residue and in the spring produce
spores called conidia. The conidia are blown by wind or splashed by raindrops
onto newly emerged corn plants in the spring. The disease became serious in the
mid-1980s as farmers switched to tillage systems that leave crop residue on the
ARS is the lead scientific agency of the U.S.
Department of Agriculture.
Scientific contact: Larry D. Dunkle, Crop Production and Pest
Control Research Laboratory, USDA-ARS, Purdue Univ., West Lafayette, Ind., phone
(765) 494-6076, email@example.com.