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Epidemiology

Slow Rusting in Oats Compared with the Logistic and Gompertz Models. H. H. Luke, U.S. Department of Agriculture, Agricultural Research Service, University of Florida, Gainesville 32611; R. D. Berger, Florida Agricultural Experiment Station, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 72:400-402. Accepted for publication 1 June 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982. DOI: 10.1094/Phyto-72-400.

Rates of crown rust development were estimated in oats that had different degrees of slow rusting. The rates were calculated with the logistic and Gompertz models for two distances from focal centers. When disease severity was low, small increases in disease caused great increases in the logistic rate (r) compared to the changes in the Gompertz rate (k). Less statistical variation existed for k values than for r values among replications, distances from infection foci, and rating periods. The logistic transformation caused considerable variation in rusting rates for individual cultivars. The Gompertz transformation was therefore more consistent at detecting degrees of slow rusting. Rates of disease progress were measured to determine the interdependence of slow rusting and late maturity. Red Rustproof, a late-maturing oat, rusted more slowly (k = 0.03–0.07) than Fulghum, an early-maturing oat (k = 0.25–0.47). Two oat selections that matured 8 days earlier than their late-maturing parent retained the slow-rusting quality (k = 0.02–0.09). Disease gradients and isopathic rates were calculated to differentiate various levels of slow rusting. No differences in the slopes of the disease gradients were observed, but the isopathic rate (1 m/day) of the susceptible cultivar (Fulghum) was significantly greater than that of the slow-rusting cultivars (0.2 m/day).