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New Biofungicide Treats Apples and Oranges Alike

By Judy McBride
December 16, 1999

Apples and oranges are all the same to biofungicides. First introduced in the United States four years ago as a result of Agricultural Research Service patents, these nontoxic biological coatings are replacing synthetic chemicals for controlling rot-causing fungi on apples, pears and citrus after harvest.

Now, ARS has signed an agreement with Micro-Flo Company of Memphis, Tenn., to finish development of the next generation of biofungicides for fruit packing houses. Micro-Flo expects to have a product on the market within two years.

Unlike the earlier biofungicides, the new coating has a kickback effect. It stops fungi that already had a toehold on the fruit, according to ARS’ Charles Wilson, who also developed one of the earlier products. Micro-Flo researcher Ahmed El Ghaouth is working with Wilson, who is at ARS’ Appalachian Fruit Research Station in Kearneysville, W.Va.

The new coating combines two bioactive substances with the yeast Candida saitoana. Innocuous to people, the yeast is a formidable competitor against the fungi that attack fresh fruits. The bioactive substances are chitosan--a naturally occurring fiber found in some weight-loss products--and a synthetic sugar used as a glucose substitute.

Chitosan acts as a natural fungicide and turns on defensive enzymes in the fruit itself. It also forms a film on the fruit that holds in carbon dioxide, thus increasing shelf life. The synthetic sugar, on the other hand, tricks the fungi into perceiving it as food, but they can’t use it.

In several years of tests in commercial packing houses in California and Florida, the new biofungicide proved as effective against rot-causing fungi as the two leading synthetic fungicides. Under the new agreement, Micro-Flo and ARS scientists will optimize its formulation and fine tune its application. ARS is the chief scientific arm of the U.S. Department of Agriculture.

Scientific contact: Charles L. Wilson, ARS Appalachian Fruit Research Station, 45 Wiltshire Rd., Kearneysville, WV 25430, phone (304) 725-3451, ext. 330; fax (304) 728-2340,