ACTIVE DISCHARGE DISTANCE OF ASCOSPORES OF VENTURIA-INAEQUALIS

Ascospores of Venturia inaequalis were discharged into still air inside small chambers from pseudothecia on small wetted bits of leaf cut from diseased apple leaves that had overwintered on the orchard floor. Ascospores were actively projected away from the leaf surface over distances ranging from 0.1 to 8.1 mm (one reached 13.2 mm). Three-quarters of the ascospores were projected less than 4.1 mm from the surface (mean distance for all ascospores was 3.0 mm). Only 1% were projected as far as 6.6 mm. The observed discharge distances were shown to be consistent with those expected from the mechanical forces acting on the ascospores.