Uredospore Dispersal from a Point Source within a Wheat Canopy

Abstract

A small infection focus of Puccinia graminis f. sp. tritici was established on susceptible plants in 2 plots of otherwise resistant wheat. Stationary 5-mm-diameter rod impaction traps were placed in the foci and at 30.5 and 61.0 cm from the foci to detect spore dispersal. The number of uredospores impacted was determined for each 10-cm height within and just above the canopy. Daily numbers of spores trapped varied greatly depending on the environment and disease severity. Within the focus, the number of spores trapped decreased with height, and only 2% of the number trapped at 10 cm above the ground were trapped above the canopy. At 30.5 and 61.0 cm horizontally from the focus, spores trapped were 4 and 2%, respectively, of the numbers trapped at the same heights within the focus. The effect of wind direction was apparent in the numbers of spores trapped at the 30.5- and 61.0-cm locations, where 10 and 5%, respectively, of the amount at the source was normally the maximum.