Control of Fusarium dry rot on postharvest Russet Burbank and Clearwater Russet potatoes by Pseudomonas biocontrol agents used alone and in combination with a chemical fungicide

Authors: Slininger, Patricia; SCHISLER, DAVID - Retired ARS Employee; OLSEN, NORA - University Of Idaho; Shea Andersh, Maureen; WOODELL, LYNN - University Of Idaho; HENDRICKS, RABECKA - University Of Idaho; MILLER, JEFF - Miller Research, Inc; Dien, Bruce

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2025
Publication Date: 4/7/2025
Citation: Slininger, P.J., Schisler, D.A., Olsen, N.L., Shea Andersh, M.A., Woodell, L.K., Hendricks, R.L., Miller, J.S., Dien, B.S. 2025. Control of Fusarium dry rot on postharvest Russet Burbank and Clearwater Russet potatoes by Pseudomonas biocontrol agents used alone and in combination with a chemical fungicide. American Journal of Potato Research. https://doi.org/10.1007/s12230-025-09989-3.
DOI: https://doi.org/10.1007/s12230-025-09989-3

Interpretive Summary: Fusarium sambucinum is a fungal pathogen that infects potato tubers through wounds to cause ‘Fusarium dry rot,’ a disease which causes greatest losses to potatoes in storage and transit worldwide and costs the global potato industry $5 billion in annual losses. The disease develops around infected wounds to form dark dry lesions that hollow and encourage secondary invasion by additional pathogens. Effective measures for its control are limited. New chemical fungicides such as StadiumTM comprised of three chemicals (azoxystrobin, fludioxonil, and difenoconazole) have shown promise but pathogen resistance to two of its components has been reported. Scientists at the National Center for Agricultural Utilization Research (NCAUR, USDA-ARS, Peoria, IL) have developed a desiccation-tolerant biological control agent for postharvest potatoes that is comprised of three beneficial bacterial strains of Pseudomonas. This triculture of bacteria has been effective in reducing several diseases in stored potatoes, including Fusarium dry rot (Fusarium sambucinum), pink rot (Phytophthora erythroseptica), late blight (Phytophthora infestans) and leak (Pythium ultimum). When sprayed to potatoes in lab and one-ton bin pilot trials, the air-dried variant triculture reduced dry rot disease by 29% on average overall and performed similarly to the freshly produced triculture (40%). The combination of triculture with Stadium reduced disease severity (75%), below that attainable by either full (68%) or reduced Stadium alone, and combination treatments of triculture with one-third strength Stadium reduced disease as well as Stadium alone at full label rate. This combination of biologicals with chemicals not only has greatest efficacy but offers multiple modes of action that would be unlikely to foster the occurrence of resistant pathogens in the future, and it provides growers with a potential broad-spectrum new tool for management of Fusarium dry rot and other postharvest potato diseases.

Technical Abstract: The biological control of Fusarium dry rot disease by a new desiccation tolerant Pseudomonas variant triculture was investigated. The triculture, formulated as an air-dried product on a dispersible carrier, can store long term at 4oC without need of freezing. Pseudomonas do not form spores, and desiccation tolerance is an important feature that allows for low-cost drying and convenient shelf-storage. In this work, the dry triculture powder was rehydrated prior to spraying to potatoes where it dries and protects wounds from pathogen infection. This research compared the efficacy of both fresh liquid and rehydrated air-dried formulations of the desiccation tolerant triculture and also assessed its benefit in combination with the chemical fungicide StadiumTM at full label and reduced rates. Three years of both laboratory and small-scale pilot trials were conducted on both Russet Burbank and Clearwater Russet potato cultivars challenged with pathogen F. sambucinum. Additional controls included no treatment (water), the sanitizer StoroxTM and BioSaveTM, which is also a Pseudomonas-based biological control product that is stored refrigerated or frozen. When all were sprayed in 0.1 mL per oz tuber, the air-dried variant triculture reduced disease by 29% on average overall and performed similarly to the freshly produced triculture (40%) and BiosaveTM. Combination of triculture with Stadium reduced disease severity (75%), below that attainable by either full (68%) or reduced Stadium alone, and combination treatments of triculture with one-third strength Stadium reduced disease as well as Stadium alone at full label rate.