<LI> Identify and characterize pathogen virulence factors important in postharvest decay.<LI> Optimize combined control strategies to reduce postharvest decay and maintain fruit quality.
PROGRESS: 2003/02 TO 2007/05<BR>
Approach: Determine virulence factors important in pathogenicity by comparing various characteristics of two pathogens of the same species, one of which is significantly less virulent than the other. Determine how environmental conditions involved in host-parasite interactions affect the virulence of the pathogen. Determine the combination of alternatives to chemical control that will equal the efficacy of fungicides in controlling postharvest plant pathogens. <P> Significant Activities that Support Special Target Populations: New treatment helps reduce postharvest fruit decay. It is necessary to find alternatives to chemical control to reduce losses due to postharvest decay. In cooperation with an ARS scientist at the Appalachian Fruit Research Station, Kearneysville, West Virginia, ARS scientists at Beltsville, Maryland, and scientists at Virginia Polytechnic Institute and State University the second year of a pilot test was completed at a commercial packing facility in Winchester, Virginia by combining controlled atmosphere storage, sodium bicarbonate, and two biocontrol agents, alone or combined, to reduce postharvest fungal decay of apples. The antagonists alone reduced blue mold decay but tended to be more effective when combined. The most effective treatment was the combination of the two antagonists and sodium bicarbonate on fruit stored under controlled atmosphere conditions. This control strategy could potentially be used commercially by the postharvest storage industry to reduce our dependency on fungicides. <P> Accomplishments: Virulence factors associated with Penicillium expansum and P. solitum during decay of apple fruit. Penicillium expansum and P. solitum are blue mold fungi that cause major losses of apples in storage due to decay. A comparison of the virulence factors produced by these fungi and the resulting decay of various varieties of apples will help us understand why P. expansum is more efficient at causing disease than P. solitum. We have purified and partially characterized the polygalacturonases produced by P. expansum and P. solitum in infected apple fruit as well as in various liquid media. It was found that both pathogens produce multiple but different forms (isozymes) of a pectin degrading enzyme known as polygalacturonase in a medium dependent fashion. In apple fruit P. expansum and P. solitum appear to produce two isoforms of the enzyme. In addition, both P. expansum and P. solitum produce cellulase activity in apple and pear fruit. Roles for the cellulase and specific polygalacturonase isozymes in the disease process are yet to be determined and are objectives of our upcoming project. This information will be of use to researchers as well as members of the apple storage industry that are exploring methods of blue mold decay control.