Temporal and Spatial Development of Bean Rust Epidemics Initiated from an Inoculated Line Source

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Abstract
Development of bean rust [Uromyces appendiculatus] in time and space was studied during 1986 and 1987 in a 30 .times. 60-m field containing 77 rows of snap beans [Phaseolus vulgaris]. The center row was inoculated and served as a 30-m line source, approximately perpendicular to the prevailing wind. Bean rust pustules were counted on the center leaflet of the trifoliolate leaves of plants at distances of 0.8 to 29.5 m from the source during the course of the epidemics. Primary disease gradients were described well by a power law. As the epidemics progressed, the disease gradients became flatter as a result of secondary spread. The major features of the development of the disease with time (t) and distance from the inoculated source (x), where P is the number of pustules per plant were described well plotting In(P) vs. A + r .cntdot. t- b .cntdot. In(x), which collapsed all 19 measured gradients onto a single curve. The parameters A, r, and b are related to the initial level of disease at the start of the epidemic, the rate of increase of the number of pustules with time, and the shape of the gradients in space, respectively.