Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2009
Publication Date: 12/18/2009
Publication URL: http://handle.nal.usda.gov/10113/41328
Citation: Slininger, P.J., Dunlap, C.A., Schisler, D.A. 2010. Polysaccharide Production Benefits Dry Storage Survival of the Biocontrol Agent Pseudomonas fluorescens S11:P:12 Effective Against Several Maladies of Stored Potatoes. Biocontrol Science and Technology. Biocontrol Science and Technology. 20(3):227-244. Interpretive Summary: Late blight is considered to be the most significant disease of potatoes worldwide, and together with pink rot and dry rot, can cause losses of well over 50% of the total harvest in storage. Chemical fungicides traditionally used to control post harvest diseases of table stock potatoes are now of little use because of genetic resistance developed by causative pathogens. Several beneficial bacteria originally found in potato field soils have been patented by ARS and are able to suppress these diseases, as well as inhibit sprouting. During cultivation, one of the bacterial strains is able to produce a viscous polymer of sugars, called a polysaccharide. We identified the polysaccharide as marginalan and then studied its role in the ability of the bacteria to protect potatoes. Marginalan was found to be important in protecting the viability of bacteria during drying and storage processes that would be typical in the production and delivery of a commercial biofungicide. Viability loss would reduce product efficacy. These findings impact the potato industry by adding to the technology base needed to successfully manufacture an effective new crop protection tool. A new tool composed of these beneficial bacteria would offer an efficient, environmentally compatible means to biologically control late blight, dry rot, and sprouting with only one treatment applied to tubers entering storage.
Technical Abstract: Pseudomonas fluorescens S11:P:12 (NRRL B-21133) is a biological control agent able to suppress several potato diseases and sprouting. Notably, it produces a polysaccharide during liquid cultivation; and the objective of this work was to determine the role of this material in the bio-control process. First, the polysaccharide was isolated, purified, and identified as marginalan, which accumulated to ~3.3 g/L in cultures. The bioactivity of isolated marginalan applied alone or in combination with washed cells of S11:P:12 was tested in potato bioassays of dry rot suppressiveness and sprout inhibition. Since the formulation and storage of a dried biocontrol product is preferred for commercial use, the impact of marginalan on cell survival during drying and storage was also studied. Washed bacteria formulated with 0-6.6 g/L polysaccharide were either applied to HyFlo granules, then slowly dried 24 h with airflow at 50-60% relative humidity, or in 1 µL droplets placed in replicate wells of a micro-plate, then quickly dried 1 h in a biohazard hood. Both 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 to 5 orders of magnitude greater, respectively, than if no marginalan were included with cells. Marginalan had no significant impact on disease or sprout suppression by S11:P:12, and its main benefit to biocontrol was viable cell preservation during drying and storage. When marginalan was formulated with other selected biocontrol strains, its benefits to drying and storage survival were again evident, though more subtle than for S11:P:12; and dry rot suppression was not impacted.