A method of testing the effect of antibacterial compounds on bacterial soft rot of potatoes, and results for preparations of dichlorophen and sodium hypochlorite

Abstract

A product containing dichlorophen as the main active ingredient was bacteriostatic against, strains ofErwinia carotovora and pectolytic clostridia in culture at concentrations equivalent to 25 mg/litre and 30 mg/litre respectively of dichlorophen. An aqueous solution of the product containing 200 mg/litre dichlorophen was rapidly bactericidal toE. carotovora var.atroseptica but a solution containing 2.3 g/litre a.i. failed to kill spores of a pectolytic clostridium. Immersion of tubers in a solution containing 200 mg/litre dichlorophen gave a concentration of about 53 mg/kg in the peel. Formulations applied as dips or sprays at concentrations of up to 2.3 g/litre dichlorophen failed to reduce the incidence of soft rot in tubers stored under <1% O2 in N2 at 100% relative humidity and 20 C for up to 11 days. BothE. carotovora and pectolytic clostridia were isolated from rots occurring after treatment of tubers with 2 g litre dichlorophen. Solutions of sodium hypochlorite (0.6–2 g litre free chlorine, pH 9.4–9.7) reduced the incidence of soft rot in unwounded tubers stored in the above conditions.