Beating back blue mold

Agricultural Research, August, 2003 by Rosalie Marion Bliss

For many an apple, without protection after harvest, the stage is set for an uneaten end. When an apple is injured, fresh fruit flesh turns soft, brown, and watery. Older lesions are sometimes invaded by a white fungus that eventually produces bluish-green spores. All this ends in a confluence of musty odors and lesions covered by fluffy fungal bodies.

The actor in this drama is Penicillium expansum, otherwise known as blue mold. It's the most significant cause of postharvest decay of stored apples in the United States. Losses from postharvest decay could be as high as 25 percent of the world's harvested fruits.

Farmers use a variety of methods to control such costly decay of fruits and vegetables. Fungicides are a common treatment to suppress postharvest decay organisms. But in keeping with the goal of farmers to reduce dependence on synthetic chemicals, Agricultural Research Service scientists have been working on developing biological controls as environmentally benign alternatives.

Biological products, such as friendly yeasts or bacteria, work by consuming nutrients in fruit and vegetable wounds that would otherwise allow rot-causing fungi to thrive. There is much interest in using normally occurring antagonistic microorganisms--decay-curbing yeasts and bacteria--as effective alternatives to fungicides.

Wojciech Janisiewicz, with ARS' Appalachian Fruit Research Station in Kearneysville, West Virginia, has filed a patent for a novel biocontrol agent aimed at neutralizing blue mold.

Janisiewicz isolated a yeast, Metschnikowia pulcherrima, that occurs naturally on buds, flowers, and fruits of apple trees. M. pulcherrima is one of several yeast species that exhibit strong antagonistic activity against postharvest decays of pome fruits, such as apples and pears.

Janisiewicz showed M. pulcherrima to be highly effective as an antagonist against blue mold--even at cold-storage temperatures--a feature of major importance to produce-warehouse operators.

The lab is now looking for a company to work with to mass-produce M. pulcherrima for commercial use.

Wojciech J. Janisiewicz is at the USDA-ARS Appalachian Fruit Research Station, 45 Wiltshire Rd., Room 333, Kearneysville, WV25430; phone (304) 725-3451, ext. 358, fax (304) 728-2340, e-mail wjanisie@afrs.ars.usda.gov.