Hot-Water Baths, Biologicals And Re-Curing Effects On Rhizopus Soft Rot During Sweetpotato Packing

Rhizopus soft rot (RSR) caused by Rhizopus stolonifer is one of the most devastating postharvest diseases of sweetpotato. It causes greatest losses when sweetpotatoes are removed from storage, washed and packed for marketing. The disease has been managed effectively by prophylactic application of synthetic fungicides on the packing line. However, there is increasing demand for alternative management strategies that do not rely on prophylactic use of synthetic fungicides. While curing immediately after harvest is a standard industry practice, re-curing after storage is not widely practised for postharvest disease management. In this study, the use of hot-water baths, biocontrol agents and re-curing after storage were investigated as potential replacements for synthetic fungicides that are widely used during sweetpotato packing. Hot-water baths at 52 degrees C for 10-15 min immediately after inoculation reduced RSR incidence by as much as 75%, but increased susceptibility to post-treatment Rhizopus infection. The biological control product Bio-Save (R) (a.i. Pseudomonas syringae strain ESC-10), used in conjunction with a 4 min water bath at 52 degrees C, gave similar protection (1.2% RSR, t = -1.7, P = 0.514) as the industry standard treatment with dicloran. Re-curing for as little as 4 h after washing roots significantly reduced RSR and deserves further evaluation to optimize conditions and determine its influence on other postharvest diseases.