VIEW ARTICLE

Density of Pythium myriotylum Oospores in Soil in Relation to Infection of Rye. D. J. Mitchell, Assistant Professor, Department of Plant Pathology, University of Florida, Gainesville 32611; Phytopathology 65:570-575. Accepted for publication 10 December 1974. DOI: 10.1094/Phyto-65-570.

Suspensions of oospores of Pythium myriotylum were sonificated to leave only oospores as viable propagules. Autoclaved Arredondo fine sand was infested with oospores, and prepared inoculum density levels were checked by plating soil samples on a selective medium. Percentages of rye infection after 5 days at 30 C in growth chambers at inoculum densities of 0, 1, 10, 25, 50, 100, 150, and 250 oospores per gram of soil were 0, 2±2, 34±3, 56±1, 71 ± 3, 81 ± 5, 100, and 100, respectively. Infection percentages after 14 days in pots in the greenhouse at the same inoculum levels were the same or slightly lower. No alterations of original inoculum densities by the formation of zoospores from oospores were observed. Although infection occurred at 25, 30, or 35 C, death of rye seedlings did not normally result at temperatures below 30 C. Plant density (one to five plants per container) did not influence the percentage of infection in short term studies, and approximately the same percentages of infection occurred at the same inoculum densities in artificially infested, untreated field soil as in infested autoclaved soil.