Head scab fungus, Fusarium graminearum, the bane of wheat crops, can be genetically disarmed. ARS scientists identified and deleted the genetic codes for an enzyme that the fungus needs to produce the toxins trichothecene. The fungus uses this toxin to infect cereal crops. Head scab steals the plant's energy, cutting its yield, and produces toxins which contaminate the grain. Head scab, which causes billions of dollars in losses each year, gets its name because it looks like scabs on the infected plant. Infections are cyclical, appearing for several years and then disappearing. However, the Midwest is currently experiencing a sustained infestation of head scab. The fungus mutates frequently, thwarting plant breeders' attempts to build resistance into host plants. Scientists say learning how to disarm the disease opens the door to finding new ways to defeat head scab and other plant diseases.
Mycotoxin Research Lab, Peoria, IL
Thomas M. Hohn, (309) 681-6380, hohntm@mail.ncaur.usda.gov

Kochia, a herbicide-resistant weed from the West, could pose a new challenge for Midwestern corn and soybean growers by the turn of the century. ARS scientists say Kochia scoparia, a member of the tumbleweed family, has already been found as far east as eastern Indiana, possibly spread by seed hitching rides on eastbound trains. Biotypes appearing in the Corn Belt resist several herbicides including triazenes (such as atrazine) and acetolactate synthase inhibitors. The weed's potential to mutate into herbicide-resistant strains is heightened because it's a prolific seed producer; each plant yields thousands of seeds. Researchers say the best time to battle this weed is early spring, when the newly germinated plant is vulnerable to herbicides in the dicamba and glyphosate chemical families. A native of Europe, kochia was introduced to the western United States by settlers. It is common in Colorado, Idaho, and Nebraska.
Crop Protection Research Lab, Urbana, IL
Loyd M Wax, (217) 333-9653, L-wax@uiuc.edu

Almond union mild etch is a new disease affecting almond trees in California, but researchers are gradually turning up clues that may lead to its treatment and prevention. If left uncontrolled, the disease could have major economic implications. Each year, California produces about $1 billion worth of almonds—65 percent of the world's crop. While most affected trees survive the disease, they are stunted and produce only two-thirds the yield of healthy trees. The disease has appeared on six almond varieties, all grafted onto a rootstock—Marianna 2624—noted for its disease resistance, especially where drainage is poor. About 5 percent of California almond trees are grafted to Marianna 2624 rootstock. Based on 4 years of field observation, ARS researchers believe the disease is not contagious and does not kill trees on its own. The most severe tree losses have occurred where the disease appeared with other stress factors: soggy soil conditions, coupled with impaired grafting that restricts the flow of carbohydrates from the leaves to the roots. Researchers speculate that a tree is already weakened by this stress, its roots become vulnerable to normally harmless soil organisms. Additional research is needed to more fully understand disease biology and to prevent outbreaks of the disease.
Crops Pathology and Genetics Research, Davis, CA
Jerry K. Uyemoto, (916) 752-0309, jkuyemoto@ucdavis.edu

Last Updated: October 28, 1997
Return to: Quarterly Report Table of Contents