Deposition Gradients of Urediniospores ofPuccinia reconditaNear a Source

Abstract

Deposition gradients of urediniospores of Puccinia recondita were measured using potted trap plants exposed at several distances between 0.1 and e.7 m downwind of a line source of spores in the middle of 0.4-ha, 1-m-tall crop. Trap plants were exposed for 2-3 hr on 8 days encompassing a range of average wind speeds of 2-5 ms-1 measured 1.5 m above the top of the crop. After exposure in the field, the trap plants were incubated and the resulting number, N, of wheat rust pustules was counted. The relative gradient of the number of pustules (dN/dx)/N, or d(ln N)/dx, decreased with distance x fromthe source. In other words, the length scale of the deposition gradient increased with distance. These results are explained in terms of a derived equation that simultaneously accounts for the combined effects of spore deposition and dilution by atmospheric turbulence and has both an exponential and a power law component.