Bio-priming Seed Treatment for Biological Control of Pythium ultimum Preemergence Damping-off in sh2 Sweet Corn. Nancy W. Callan, Associate Professor, Western Agricultural Research Center, Montana State University, Corvallis 59828. D. E. Mathre, and James B. Miller. Professor, Department of Plant Pathology, Montana State University, Bozeman 59717; and Research Technician, Western Agricultural Research Center, Montana State University, Corvallis 59828. Plant Dis. 74:368-372. Accepted for publication 29 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0368.

Sweet corn (Zea mays) with the sh2 gene for enhanced sugar content is highly susceptible to preemergence damping-off, caused primarily by Pythium ultimum in Montana’s Bitterroot Valley. Rhizosphere bacteria that adhered to hyphae of P. ultimum and were antagonistic to the growth of this pathogen were isolated from Bitterroot Valley soils. An isolate of Pseudomonas fluorescens, AB254, provided superior seed protection from Pythium damping-off in naturally infested soils. At least 1 × 10⁷ cfu per seed of AB254 was needed to achieve maximum protection. In a process we have termed “bio-priming,” dry seed was coated with P. fluorescens AB254 and allowed to imbibe water under warm temperatures until a 35–40% moisture content was achieved. During bio-priming, bacterial populations increased from 10 to over 10,000-fold, depending on initial inoculum level. Bio-priming provided protection against damping-off as good as or better than seed treatment with metalaxyl when the seeds were planted in cold soil. This process may be of interest and value to growers who wish to plant sweet corn or other temperature-sensitive crops into cold soils where damping-off is a problem and the use of chemical seed treatments is not desired.