Population Dynamics of Pythium spp. in Soil Planted with Peanut. R. K. Soufi, Former Research Assistant, Department of Plant Pathology, Oklahoma State University, Stillwater 74078. A. B. Filonow, Associate Professor, Department of Plant Pathology, Oklahoma State University, Stillwater 74078. Plant Dis. 76:1203-1209. Accepted for publication 28 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1203.

Populations of Pythium spp. in Oklahoma field soils planted with peanut had distinctive temporal patterns to their fluctuations during the growing season. Temporal patterns occurred in three different peanut-growing areas of Oklahoma in dissimilar soils planted to different cultivars. Two general types of temporal patterns were observed, both occurring after initiation of pegging and pod development. The most frequently encountered pattern was an increase in population to a maximum, followed by either a sharp or a gradual decline. The other pattern was a gradual population increase during the season, reaching a maximum at harvest. Populations of Pythium spp. in fallow soil in field plots at the Caddo Research Station, Ft. Cobb, Oklahoma, in 1989 and 1990 fluctuated randomly, whereas populations in adjacent plots planted to peanut peaked several weeks after pegging, then rapidly declined by harvest. The temporal pattern of the population peak and decline was re-created in growth chambers using field soil planted with peanut. In these studies, greater populations of Pythium spp. were found in field soil containing peanut roots and/or pods than in soil without roots and pods. At the Caddo Research Station, the frequency of isolation of Pythium spp. from pods increased with pod age; however, maximum isolation frequency from pods was not synchronous with the peak populations of Pythium spp. in soil but occurred 1–2 mo after the population peaks. These results suggest that colonization of pods by Pythium spp. may be regulated by pod development.