VIEW ARTICLE

Ecology and Epidemiology

Influence of Soil Water Potential and Temperature on Severity of Pythium Root Rot of Snap Beans. D. J. Pieczarka, Graduate Research Assistant, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456, Present address of senior author: Agricultural Research and Education Center, University of Florida, Belle Glade, FL 33430; G. S. Abawi, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456. Phytopathology 68:766-772. Accepted for publication 28 October 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-766.

Soil water and temperature had significant effects on the severity of root rot of snap beans caused by Pythium ultimum. The disease was studied in pasteurized soil infested with the pathogen and maintained at fluctuating water potentials of 0 to –1,0 to –5, and 0 to –12 bars, each at 15, 21, and 27 C. At any one temperature, root-rot severity increased as soil water potential increased. At any one water potential, root-rot severity decreased as soil temperature increased. Pythium root rot was most severe and caused the greatest plant dry weight loss in soil at 15 C and soil water potential of 0 to –1 bar. When plants grown in infested soil for 15 days at 15 C and at soil water potential of 0 to –1 bar were shifted to 27 C and/or soil water potential 0 to –5 bars for another 15 days, they had greater dry weight and less root rot than did plants maintained in soil at 15 C and 0 to –1 bar for 30 days. Damage from Pythium also occurred, although to a lesser extent, when plants were grown at 27 C and soil water potential of 0 to –12 bars for 15 days and then shifted to a 15 C and/or soil water potential of 0 to –1 bar. Soil populations of P. ultimum increased at all temperatures and soil water potentials tested.