Effects of Water Temperature, Inoculum Concentration and Age, and Sanitizers on Infection of Ceratocystis fimbriata, Causal Agent of Black Rot in Sweetpotato

Abstract

Black rot, caused by Ceratocystis fimbriata, is a devastating postharvest disease of sweetpotato that recently re-emerged in 2014. Although the disease is known to develop in storage and during export to overseas markets, little is known as to how pathogen dispersal occurs. This study was designed to investigate dump tank water as a means of dispersal through four different types of water treatments: inoculum concentration (0, 5, 5 × 101, 5 × 102, and 5 × 103 spores/ml), inoculum age (0, 24, 48, 96, and 144 h), water temperature (10°C, 23°C, 35°C, and 45°C), and presence of a water sanitizer (DryTec, SaniDate, FruitGard, and Selectrocide). Wounded and nonwounded sweetpotato storage roots were soaked in each water treatment for 20 min, stored at 29°C for a 14-day period, and rated for disease incidence every other day. Disease was observed in sweetpotato storage roots in all water treatments tested, except in the negative controls. Disease incidence decreased with both inoculum concentration and inoculum age, yet values of 16.26% and up to 50% were observed for roots exposed to 5 spores/ml and 144-h water treatments, respectively. Sanitizer products that contained a form of chlorine as the active ingredient significantly reduced disease incidence in storage roots when compared with control roots and roots exposed to a hydrogen-peroxide based product. Finally, no significant differences in final incidence were detected in wounded sweetpotato storage roots exposed to water treatments of any temperature, but a significant reduction in disease progression was observed in the 45°C treatment. These findings indicate that if packing line dump tanks are improperly managed, they can aid C. fimbriata dispersal through the build-up of inoculum as infected roots are unknowingly washed after storage. Chlorine-based sanitizers can reduce infection when applied after root washing and not in the presence of high organic matter typically found in dump tanks.