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Epidemiology of Cercosporella Footrot of Wheat: Spore Production. R. C. Rowe, Former graduate student, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Present address of senior author: Plant Pathology Department, North Carolina State University, Raleigh 27607; R. L. Powelson, Associate Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 63:981-984. Accepted for publication 15 February 1973. DOI: 10.1094/Phyto-63-981.

Maximum sporulation by Cercosporella herpotrichoides occurred at 10 C and decreased to insignificant levels above 20 C and below 0 C, when incubated at constant temperature. Under alternating high and low temperatures, the fungus continued to sporulate moderately when temperatures were in the optimal range (8-12 C) as long as the duration below 0 C did not exceed 14 hrs. Sporulation was reduced or prevented if daily temperatures were above 20 C for 10 hr, even if favorable temperatures (8-12 C) occurred during the rest of the day. A value which reflects the influence of fluctuating temperature regimes on sporulation was developed which was designated the “Daily Thermal Sporulation Coefficient” (DTSC). This value is based on the temperature-sporulation curve for C. herpotrichoides and is a function of the total hours of favorable and unfavorable temperatures that occur daily. Active sporulation periods are defined as periods of at least 2-3 weeks during which the humidity near the soil remains near saturation, the air temperature is above freezing for more than 8 hr/day, and the average DTSC is above 50. If these conditions are maintained continuously, maximum levels of sporulation can occur for up to 50 days. Sporulation periods can be identified from field temperature data and used to assess the seasonal epidemic potential.