Epiphytology of Puccinia striiformis at Five Selected Locations in Oregon During 1968 and 1969

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Abstract
Epiphytological studies were conducted on stripe rust of wheat [Triticum aestivum] in NE Oregon [USA] during 1968-69. Five plot locations provided varied climates. Plants in the 3- to 4-leaf stage at the center of each plot were inoculated with uredospores of P. striiformis at a dosage rate of 25 g/ha. Spread and build-up of the stripe rust pathogen was closely followed during the growing season. Temperature, relative humidity and dew formation were monitored within the plant stand. The pathogen-spread patterns indicated that the inoculated centers served as the only or the predominant source of initial inoculum. The epiphytotics of 1969 progressed more rapidly than those of 1968 with disease increase rates of 0.28-0.04. Upwind and downwind infection gradients and rates of disease increase were calculated for all plots. Yields varied sharply within and among plots. The data apply to the development of a predictive model of a stripe rust epiphytotic.

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