ESCAPE OF UREDINIOSPORES OF UROMYCES-PHASEOLI FROM A BEAN FIELD CANOPY

Vertical profiles of wind speed and aerial concentration of urediniospores of Uromyces phaseoli were measured on several occasions above a 0.25-ha field of bean plants [Phaseolus vulgaris] severely diseased with U. phaseoli. The aerial concentrations of single (singlets) urediniospores and of clusters of two (doublets) and three (triplets) urediniospores were determined separately, and the upward flux at 0.5 m above the canopy was calculated for each. The upward flux, or escape, of singlets ranged between 6 and 31 spores per square meter per second and was about 2-7 times greater than the escape of doublets and about 5-30 times greater than the escape of triplets. The relative proportions of singlets, doublets, and triplets escaping the canopy agreed with the proportions of each released by the crop, as assessed by the relative numbers of each caught on horizontal, sticky glass slides placed within the crop.