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Effect of Temperature, Light, and Dew Duration on Relative Numbers of Infection Structures of Puccinia coronata avenae. Kathleen Politowski, Graduate Research Assistant, Department of Botany and Plant Pathology, Iowa State University, Ames, Iowa 50011; J. Artie Browning, Professor of Plant Pathology, Department of Botany and Plant Pathology, Iowa State University, Ames, Iowa 50011. Phytopathology 65:1400-1404. Accepted for publication 26 June 1975. DOI: 10.1094/Phyto-65-1400.

In a cam-programmable dew-deposition environment chamber, essentially all germination by Puccinia coronata avenae uredospores occurred on oat leaves within the first 2 hours of a 21.0 C dew period. A few appressoria formed within 2 hours, but no penetration occurred until after 4 hours of dew. Five hours of dew at 21.0 C was the practical minimum for infection. After 16 hours of dew at 21.0 C, there was no further increase in numbers of germ tubes, appressoria, penetration tubes, or pustules. Temperatures of 15.5, 21.0, and 26.5 C favored germination equally, but 10 C was less favorable. Once germination occurred, appressoria formed equally well from 10.0-26.5 C. Optimum dew period temperatures for penetration and pustule formation were 15.5 and 21.0 C. An initial 12-hour dew period at 21.0 C followed by 4 more hours of dew at 21.0 C resulted in the same number of pustules as one followed by 4 hours of dew at 26.5 C, and more pustules than one followed by 4 hours of dew at 17.0 C. A variable temperature regime that simulated natural night-time dew conditions resulted in fewer pustules than constant 15.5 or 21.0 C dew periods. Light (8,600 lux) near the end of the dew period did not enhance penetration or pustule formation by P. coronata, but it did for P. graminis tritici and P. graminis avenae.

Additional keywords: Avena sativa, Triticum aestivum, epidemiology, Puccinia graminis tritici, P. graminis avenae.