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Ecology and Epidemiology

Patterns of Bean Rust Lesion Size Increase and Spore Production. M. W. Imhoff, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650; K. J. Leonard(2), and C. E. Main(3). (2)(3)Plant pathologist, USDA, ARS; and professor, respectively, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 72:441-446. Accepted for publication 8 July 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-72-441.

Urediospores of Uromyces phaseoli var. typica were collected daily from first trifoliolate leaves of Phaseolus vulgaris grown under controlled conditions at 16, 21, 24, and 27 C. Nine lesion densities ranging from 11 to 107 lesions per leaflet, three relative humidities ranging from 51 to 87%, and two leaf ages were incorporated into the four temperature treatments. The latent period varied from 9 days at 16 C to 7 days at 24 C. Sporulation per lesion occurred in waves of decreasing amplitude over time in most treatments. Increase of total lesion area, sporulating area, and cumulative numbers of spores, however, was nearly linear with time in all treatments, except at 27 C where lesions did not develop. The average ratio of sporulating area to total lesion area was 0.27. Relative humidities between 51–87% and lesion densities ranging from 11 to 107 lesions per leaflet significantly affected cumulative spore production, but accounted for only a small part of the variation among treatments. The rates of increase of both sporulating area and total infected area could be described by quadratic temperature functions (r² = 0.988 and 0.956, respectively). Efficiency of both sporulating and total infected areas (sporulation per unit area) varied negatively quadratically with temperature, inversely with lesion density, and positively with leaf age. The average rate of sporulation per day appeared to be inversely proportional to lesion density over all temperature and humidity treatments. Quantitative information obtained in this study can be used to form a preliminary mathematical description of sporulation in the bean rust pathosystem.