Survival and Germination of Urediniospores of Puccinia recondita and P. graminis

Reproducible, uniform inoculum distribution was obtained using a settling tower and transfer paper technique to measure effect of temperature, moisture, light intensity, and host : parasite combination on viability and survival of urediniospores of Puccinia recondita and P. graminis. Significant differences were observed on water agar plates at the P = 0.05 level in percentage of germination among cultures of both species. Significant differences were observed on host leaves at the P = 0.10 level in percentage germination among host : parasite combinations. Germination percent decreased with age of the urediniospore in both species. Increasing light intensity from levels found in the canopy on cloudy days to the intensity found in full sunlight at the top of the canopy significantly increased germination of spores. Survival of urediniospores suspended in the atmosphere was significantly longer during summer conditions than during winter conditions. Wheat leaf and stem rust, incited by Puccinia recondita Rob. ex Desm. f. sp. tritici and P. graminis Pers. f. sp. tritici, respectively, have reduced wheat (Triticum aestivum L.) yields by as much as 50% in the Great Plains region of the USA (Samborski and Peterson, 1960; Eversmeyer and Bender, 1974). Viable urediniospores and dormant mycelia are the principal inoculum sources (Burleigh et al., 1969) that contribute to the early spring establishment of the disease and the eventual development of an epidemic in the Central Great Plains. Given the early occurrence of the disease (Eversmeyer et al., 1988), favorable environments and compatible host: parasite inter