Postharvest Biological Control of Fusarium Dry Rot: Application Development

Postharvest Fusarium dry rot of potatoes is a serious problem worldwide. When produced as a triculture of Pseudomonas sp., the biological control agent (BCA) suppresses Fusarium dry rot decay, late blight, pink rot, Pythium leak and sprouting in storage. It does so via multiple control mechanisms, thus minimizing risk of pathogen resistance. Tricultures were produced in 75-mL flask cultures, concentrated, applied to Kenite 700 diatomaceous earth carrier, then air dried at ~20-25 C and 60% relative humidity to 2-5% moisture, and stored at 4 C. The following variables were examined to help guide postharvest application technologies toward compatibility with conditions and practices of the potato industry and an evolving bioeconomy: BCA growth media (synthetic or unrefined cellulosic sugars); surfactants to improve spray coverage (Break-Thru S 301 organic, Break-Thru SD 260, or none); BCA dosage for most economical efficacy (33, 67 or 100% strength); minimal spray volume for equivalent BCA delivery (0.06 or 0.1 mL/oz tuber); dry BCA storage time (5-6 d or 3 mos); and BCA rehydration (with or without overnight nutrient rehydration). In laboratory assays, 10 tubers per treatment were inoculated with a conidial suspension of Fusarium sambucinum, let dry 15 min, then wounded twice (once per side) with a 2 mm (length x diameter) steel post, and sprayed with BCAs or water control. Following 28 d incubation at 15 C 95% RH, dry rot disease reduction by BCAs ranged from 84% to 38%. In a parallel larger pilot experiment of similar design (in progress), four replicates of 20 potatoes were inoculated with conidia, incubated covered 45 min, wounded by tumbling across chains/rebar, treated and stored 90 d (45 F, 95% RH, 1cfm/cwt air) to assess disease development. Results from both studies will provide BCA production criteria, application methodology and efficacy data to support postharvest use in the potato industry.
Extension, Production, and Management