PARASITISM OF UNCINULA-NECATOR CLEISTOTHECIA BY THE MYCOPARASITE AMPELOMYCES-QUISQUALIS

Parasitism of Uncinula necator cleistothecia by the mycoparasite Ampel omyces quisqualis was widespread in the Vitaceae around New York State . Although A. quisqualis did not survive in naturally parasitized U. n ecator cleistothecia on grape leaves, it did overwinter in parasitized cleistothecia on the bark of grapevines. Although only 1% of the tota l population of cleistothecia on bark was parasitized, the bark may st ill be an important site for overwintering of A. quisqualis since the mycoparasite is located adjacent to developing powdery mildew colonies on leaves, analogous to that of healthy cleistothecia, which also ove rwinter on bark and release primary inoculum to infect emerging grape leaves. In vitro studies of parasitism of U. necator cleistothecia sho wed that infection occurs only during early stages of development prio r to or at the earliest stages of the formation of appendages but befo re darkening of the cleistothecial wall. When A. quisqualis was applie d to grapevines from colonized cotton-wick cultures suspended above vi nes, parasitism of cleistothecia on leaves increased compared to natur ally occurring parasitism, although during a season with high rainfall the level of parasitism was similar by the end of the season. The imp act of increased parasitism was a reduction in the number of cleistoth ecia dispersed from leaves to bark and a reduction (50 to 60%) in the number of cleistothecia overwintering on bark of grapevines. Thus, bio logical control of grape powdery mildew with A. quisqualis may be furt her enhanced by a reduction in the level of overwintering inoculum for the next season.