ARS | Publication request: Polysaccharide benefits dry storage survival of the biocontrol agent Pseudomonas fluorescens S11:P:12 effective against several maladies of stored potatoes

Submitted to: Phytopathology
Publication Type: Abstract
Publication Acceptance Date: July 30, 2008
Publication Date: July 26, 2008
Citation: Slininger, P.J., Dunlap, C.A., Schisler, D.A. 2008. Polysaccharide benefits dry storage survival of the biocontrol agent Pseudomonas fluorescens S11:P:12 effective against several maladies of stored potatoes [abstract]. Phytopathology 98(6):S147. . American Phytopathological Society.

Technical Abstract: Pseudomonas fluorescens S11:P:12 (NRRL B-21133) is a biological control agent able to suppress several storage maladies of potatoes including sprouting, Fusarium dry rot incited by Gibberella pulicaris, pink rot incited by Phytophthora erythroseptica, and late blight incited by Phytophthora infestans US-8 mating type A2. One characteristic of this strain is that it produces a polysaccharide during liquid cultivation, and our objective here was to determine if this product had a role in the bio-control process. First, the polysaccharide was isolated, purified and identified as marginalan, which in cultures accumulated to about 3.3 g/L (defined as 1X concentration). The bioactivity of isolated marginalan applied alone and in combination with washed cells of P. fluorescens (2 x 10e10 cells/mL buffer) was tested at the 0, 1/3 X, 1 X, and 2X levels in wounded potato assays of dry rot suppressiveness and potato eye core assays of sprout inhibition. Since the formulation and storage of a dry biocontrol agent is desirable for commercial use, the impact of marginalan on cell survival during drying and storage was also examined when washed bacteria formulated at 0, 1/3 X, 1 X, and 2X polysaccharide were applied under two conditions: either in 2 mL/g HyFlo® then dried 24 h with airflow at 50-60% relative humidity; or in 1 micro-L droplets placed in replicate wells of a micro-plate dried 1 h in a biohazard hood. Both the Hyflo® and micro-plate dry storage results indicated that marginalan significantly reduced cell death after drying, such that the final stable viable cell density was 2.5 or five orders of magnitude higher (respective to storage condition) than if no marginalan were included with the cells. Marginalan had no significant impact on either disease or sprout suppression by S11:P:12, and so its main benefit to biocontrol was viable cell preservation during drying and storage.