Spatial and Temporal Spread of Oat Crown Rust

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Abstract
The spread of oat crown rust (caused by P. coronata) in time and space was measured equally well by disease severity assessed on whole plants or on the leaf below the flag leaf (F-1) for [oat, Avena byzantina] cultivars fulghum (susceptible) and Burt (intermediate). The assessment of leaf F-1 on ''Red Rustproof-14'' (resistant) underestimated the total proportion of disease (x). The average apparent infection rates (r) for rust on whole plants of ''Fulghum'' and ''Burt'' were 0.4, and 0.35 units/day, respectively. These rates were significantly faster than that for ''Red Rustproof-14'' (r = 0.2). Rust isopaths spread outward from plot centers at rates that averaged 0.9, 0.4 and 0.35 m/day for ''Fulghum'', ''Burt'' and ''Red Rustproof-14'', respectively. The rate of isopath movement also was used to measure interplot interference. On ''Red Rustproof-14'', isopath movement increased from 0.2 to 1.2 m/day when secondary foci enlarged. Rust increased equally fast (as measured by r) at centers and peripheries of foci. There was no flattening of disease gradients for ''Burt'' for ''Fulghum'' when logit x was plotted against log10 d (distance). The log10 x vs. log10 d transformation for disease gradients provided an aberration of true gradients.

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