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

The biological control of Fusarium dry rot of potato by a new desiccation tolerant Pseudomonas variant triculture was investigated. Pseudomonads do not form spores, and desiccation tolerance is key to low-cost drying, convenient shelf-storage, and successful application. The triculture, formulated as an air-dried product on a dispersible carrier, can store long term at 4 C without need of freezing. 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 assessed their benefit in combination with the chemical fungicide Stadium^R (actives azoxystrobin + fludioxonil + difenoconazole). Three years of both laboratory and small-scale pilot trials were conducted on both Russet Burbank and Clearwater Russet potato cultivars to assess efficacy against the pathogen F. sambucinum. Additional controls included no treatment (water), the sanitizer StorOx^R 2.0 (hydrogen peroxide + peroxyacetic acid), and Bio-Save^R 10 LP, which is a Pseudomonas syringae-based biological control product that is stored refrigerated or frozen. When all were sprayed in 3.527 mL kg⁻¹ tuber, the air-dried variant triculture reduced disease by 29% on average and performed similarly to the freshly produced triculture (40%) and Bio-Save^R. Combination of triculture with Stadium^R reduced disease severity by 75%, which is below that attainable by Stadium^R alone at either full (68%) or one-third strength, and combination treatments of triculture with reduced Stadium^R controlled disease as well as Stadium^R alone at full label rate.