GENOMICS AND ENGINEERING OF STRESS-TOLERANT MICROBES FOR LOWER COST PRODUCTION OF BIOFUELS AND BIOPRODUCTS
Location: Crop Bioprotection Research
Title: Multi-Strain Co-Cultures Surpass Blends for Broad Spectrum Biological Control of Maladies of Potatoes in Storage
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 2010
Publication Date: September 1, 2010
Citation: Slininger, P.J., Schisler, D.A., Shea Andersh, M.A., Sloan, J.M., Woodell, L.K., Olsen, N.L., Frazier, M. 2010. Multi-strain co-cultures surpass blends for broad spectrum biological control of maladies of potatoes in storage. Biocontrol Science and Technology. 20(8):763-786.
Interpretive Summary: A more cost-effective process has been developed for manufacturing a broad spectrum biological treatment to control maladies of potatoes in storage. 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. Additionally, the most common sprout inhibitor on the market is facing stricter regulation due to public health and safety concerns. Four 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. Our prior research has shown that formulations containing multiple kinds of bacteria more consistently control potato maladies than those with only one kind. Despite the apparent advantages of applying strain mixes, the disadvantages for the manufacturer are increased capital and operating costs to manage a different fermentation for each strain used in a mix. As a result of a three-year study involving both laboratory and small pilot simulations of potato storages, we found that it is possible to more cost-effectively co-culture strains together in one fermentor. Additionally, this process stimulates inter-strain activities to boost biocontrol efficacy and consistency beyond that achievable by the more costly method of growing strains in separate fermentations and mixing just prior to addition to potatoes. 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.
Pseudomonas fluorescens strains S11:P:12, P22:Y:05, and S22:T:04 and Enterobacter cloacae strain S11:T:07 have been documented to suppress four important storage potato maladies: dry rot, late blight, pink rot, and sprouting. This research investigates the efficacy and consistency of strain mixtures produced by co-culturing strains together in one vessel or by blending them together after separate cultivations in pure cultures. Pure and co-cultures were produced in flask or fermentor cultures, viable cell concentrations were assessed using a nutrient-based selective plating method to identify and enumerate strains, and the efficacy of treatments was assessed with respect to dry rot, pink rot, late blight or sprout suppression. Experiments were designed to analyze dry rot suppression versus all strain combinations and the combination method (co-culture or blend). Results of a two-way analysis of variance of disease with strain composition and combination method showed that significantly better dry rot suppression was obtained by co-cultures (30.3 + 2.4% relative disease) than by similar strain blends of pure cultures (41.3 + 2.4%) (P < 0.001). During a three-year study, both biocontrol efficacy and consistency were assessed in 16 laboratory and small pilot trials simulating commercial storages. Three-strain co-culture had a lower mean disease rating than the blend in 9 of 16 experiments examining control of the three diseases and sprouting. The co-culture led other treatments in incidences of significant malady reduction relative to the control: 14 of 16 attempts for co-culture, 11 of 16 attempts for blend, 10 of 13 attempts for pure S11:P:12, 8 of 13 attempts for S22:T:04, and 9 of 13 attempts for P22:Y:05. Using relative performance indices to rank treatment performance across all experiments, the co-culture treatment ranked significantly higher than the blend. A synergy analysis suggested that co-culturing strains stimulated inter-strain activities to boost biocontrol efficacy and consistency, a feature not developed in strains grown separately and mixed just prior to addition to potatoes.