Location: Crop Bioprotection ResearchTitle: Appraisal of selected osmoprotectants and carriers for formulating Gram-negative biocontrol agents active against Fusarium dry rot on potatoes in storage Author
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2016
Publication Date: 3/12/2016
Citation: Schisler, D.A., Slininger, P.J., Olsen, N.L. 2016. Appraisal of selected osmoprotectants and carriers for formulating Gram-negative biocontrol agents active against Fusarium dry rot on potatoes in storage. Biological Control. 98:1-10. doi: 10.1016/j.biocontrol.2016.03.009.
Interpretive Summary: ARS research scientists in Peoria, IL have previously discovered biocontrol agents that reduce one or more potato tuber storage problems including dry rot, late blight and sprouting. While these biocontrol agents are extremely effective, developing a method for air-drying this type of biocontrol agent would greatly improve the chance of making an economical biocontrol product from them. In this study, we discovered that the sugars fructose and trehalose protected cells of these biocontrol agents from dying during drying better than any of the other sugars tested. Similarly, we found that two types of diatomaceous earths (DE) enhanced the viability of cells of biocontrol agents after air-drying. Dried products made of biocontrol agents and superior sugars and DE reduced dry rot by 20 to 60% in laboratory and small pilot-scale tests. These results represent a significant step towards the production of a new disease management tool for reducing the impact of several critical problems faced by potato growers and storage managers.
Technical Abstract: The production of a dry formulation containing a high titer of viable cells of a Gram-negative biological control agent is a challenging and critically important step in developing the agent into a commercial product. Producing a dry formulation using methods based on air-drying is especially attractive economically. Pseudomonas fluorescens strains S11P12, P22Y05, and S22T04 reduce Fusarium dry rot of potatoes in storage. The relative number of cells of each strain that survived air-drying after 24 h of cell growth in a liquid medium and treatment with carbohydrate-based osmoprotectants was determined using a high-throughput microtiter plate assay. Fructose and trehalose at 20 g L**-1 were the most effective osmoprotectants when results were pooled across strains (P=0.05, FPLSD) though osmoprotectant influence on cell survival varied between strains. Different grades of diatomaceous earth, perlite, fumed silica and clay were then combined with suspensions of washed cells of each strain. After 15-18 h in an air-drier with relative humidity controlled at 50-60%, two diatomaceous earth products were superior in maintaining cell viability though, in the absence of osmoprotectants, log10 CFU g**-1 of these products dropped by 3 or more log units 24 h after drying. Air-dried products resulting from combining cells suspended in 20 g L**-1 trehalose or fructose with the diatomaceous earth products often reduced Fusarium dry rot by >60% (P=0.05) for strains P22Y05 and S22T04 but S11P12 products were not as effective in laboratory assays. In a small pilot-scale test, dry formulations of these strains and a combination of the fungicides fludioxonil,azoxystrobin and difenoconazole reduced dry rot by approximately 20% and 55%, respectively (P=0.05).