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For potatoes - stopping dry rot without chemicals.

Potato dry rot--a dry, crumbly decay of the potato tuber-may soon be controlled with a natural bacterial agent instead of a synthetic chemical.

"Dry rot is caused by a fungus, Fusarium sambucinum, that affects potatoes both in the field and in storage," explains David A. Schisler, a plant pathologist at the National Center for Agricultural Utilization Research in Peoria, Illinois. "The fungus enters potatoes through wounds in the skin. Losses due to this disease have been reported to be as high as 60 percent in storage."

Under proper conditions, potatoes are capable of healing their wounds within a few weeks following injury. But during this time, tubers are susceptible to infection, so scientists are searching for a microbial biological control that would be active throughout this period of vulnerability.

Schisler and Pattiria Slininger, a chemical engineer at the center, have found bacteria that reduce the size of affected areas and, in some cases, totally prevent the disease.

The disease-fighting bacteria are from soil samples gathered in 1990 from Wisconsin potato fields. The scientists initially found 18 strains that showed promise as biological controls against dry rot. Since then, they've narrowed the field to six by evaluating strains for both effectiveness and ease of mass production.

Growers now use a chemical, thiabendazole (TBZ), to control the disease. It has been used for about 20 years and is the only fungicide approved for postharvest treatment of dry rot. However, recent studies indicate that 75 percent of field isolates of the fungus are completely resistant to TBZ.

"There's a control void here that microbial biological agents are well-suited to fill," says Schisler.

A patent application has been filed. Further work will involve development of liquid culture and formulation technologies needed to produce the bacteria as storable, effective biocontrol agents.

Explains Slininger, "The conditions applied during mass production of the bacteria in liquid culture will likely affect the physiology, vigor, and, hence, efficacy of the bacterial cells harvested."

To preserve cell viability and facilitate crop treatment, scientists are considering a wettable powder formulation of dried bacterial cells and a carrier. Such a product would be handled and applied much like the wettable powder fungicide currently in use.--By Marcie Gerrietts, ARS.

Dave Schisler and Pat Slininger are in the USDA-ARS Fermentation Biochemistry Unit at the National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL 61604. Phone (309) 685-4011, fax number (309) 671-7065.
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Author:Gerrietts, Marcie
Publication:Agricultural Research
Date:Jun 1, 1993
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