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Cotton Under Glass--New Clues on AflatoxinBy Jill Lee
NEW ORLEANS, Jan. 8--Ever been to a cotton forest? Thats what youll see if you visit microbiologist Maren Klichs laboratory at the Southern Regional Research Center in New Orleans.
In greenhouses at the Agricultural Research Service, USDA facility, cotton plants grow in white plastic tubes about five feet long. The reason: to allow the cottons tap roots to reach their full length, so they live in conditions that mimic a farmers field. Pink and white flowers, green leaves and soft white bolls grow high overhead, reaching for the skylight.
But pity the plants in this hot house--they serve as a small-scale model of what happens when the fungus Aspergillus flavus attacks a field. Droughts seem to spur outbreaks of the fungus, which produces a natural carcinogen known as aflatoxin. While there is no abandon hope sign on the greenhouse door, there is a warning posted by Klich not to water the cotton without her knowledge. All the cotton is infected and the temperature is kept high.
Aflatoxin does not interfere with cotton fiber quality, but it is hazardous to humans and livestock, so it does matter when growers want to sell cottonseed. The Food and Drug Administration has set guidelines concerning the contaminant--less than 20 parts per billion is permitted for food-grade products. One part per billion is equal to a drop of water in a 21,700-gallon swimming pool. Aflatoxin contamination of cottonseed can be a major problem in the West, robbing growers of valuable side products such as oil and meal.
What were trying to do is develop a model for how fungi such as A. flavus take hold in plants when theres no wound or easy opportunity for infection, Klich said. We want to look at all the factors in the field--not only heat and drought conditions, but also wind, nitrogen levels and other factors nobodys thought about yet.
Klichs most recent findings suggest that cotton plants may have a symbiotic relationship with A. flavus when drought or other environmental stress occurs. The cotton may not be able to produce some needed chemicals during drought and may be using something in the fungus to replace what it cant produce under dry, hot conditions, Klich said.
If thats happening, we could supplement drought-stressed plants with whatever chemical they are missing, so they wouldnt need the fungus anymore, she continued. The trick is confirming the relationship and then finding out exactly what this substance--or combination of substances--the plants lack.
In earlier experiments, Klich was able to prove that A. flavus infections move in one direction--up. She found that if she inoculated a plant with A. flavus at the natural openings near the top, the infection would not move down the stem, but infections that started at the plants stem did travel upwards. This discovery has led her to believe openings in the roots might be another pathway to infection.
To the growers, this research may seem basic, said Klich. But I see it as an opportunity to find solutions for the industry by exploring everything that happens when A. flavus invades a cotton host. If we know how it gets in, we may be able to close the doors to infection.
Scientific contact: Maren Klich, Food and Feed Safety Research, Southern Regional Research Center, Agricultural Research Service, USDA, New Orleans, La. 70179. Telephone (504) 286-4361, fax (504) 286-4419, email email@example.com