Growth of Uredinia ofPuccinia reconditain Leaves of Slow- and Fast-Rusting Wheat Cultivars

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Abstract
Rates of expansion of the surface areas of uredinia of P. recondita in flag leaves of slow- and fast-rusting wheat cultivars (as judged by latent period and final uredinium size) were studied. Uredinia grew linearly with time and at a significantly faster rate in fast-running cultivars than in slow-rusting cultivars. Average rates for fast-running ''Morocco'', ''Monon'' and ''Suwon 92'' were 0.07, 0.05 and 0.04 mm2/day, respectively. Average rates for slow-rusting ''CI 13227'' and ''Suwon 85'' were 0.03 and 0.02 mm2/day, respectively. Uredinia reached maximum size 8-10 days after first becoming visible. The more densely uredinia were packed on a leaf, the slower they grew. Simulations of leaf rust epidemics suggested that a slow growth rate of uredinia would be a significant factor in retarding disease development in the field.