VIEW ARTICLE

Effect of Soil Treatment, Soil Temperature, and Plant Age on Pythium Root Rot of Cotton. R. W. Roncadori, Associate and Assistant Professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30601; S. M. McCarter, Associate and Assistant Professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30601. Phytopathology 62:373-376. Accepted for publication 28 October 1971. DOI: 10.1094/Phyto-62-373.

Methyl bromide or sodium-p-(dimethyla-mino) benzenediazosulfonate (Dexon) treatment of soil, collected from a problem field where stunting and root rot were present, stimulated cotton growth in plant growth chambers. A greater growth response occurred with a warm-cold-cool temperature regime than with a warm-cold-warm regime. Pythium debaryanum and P. irregulare were isolated frequently from necrotic roots in untreated soil. Pentachloronitrobenzene (Terraclor) increased root and shoot growth at the higher temperature regime, however, indicating that other members of the soil microflora were involved in stunting. Both P. debaryanum and P. irregulare decayed young secondary roots, and reduced plant height at day-night temperatures of 23 and 13 C in artificially infested soil. Pythium irregulare caused root necrosis and retarded shoot growth at constant temperatures of 15 and 19 C, but not from 23 to 31 C. Root rot was evident on plants 10, 20, and 30 days old at 18 C; however, disease severity generally decreased as plant age increased. Although Pythium spp. may cause root rot of established plants, their role in stunting in the field is probably confined to the early portion of the growing season, as soil temperatures unfavorable for disease development occur during the summer, and host resistance increases with age.