Lipopeptides Fengycin and Iturin A as postharvest fungicide on pome fruit

Cyclolipopeptides (CLP) iturin A and fengycins, produced by Bacillus amyloliquefaciens (DMS 23117) are potential biological fungicides. The aim of this study is to evaluate the efficacy of CLPs on fruit infected with Botrytis cinerea (causing grey mould on pears) and Penicillium expansum (causing blue mould on apples) and investigate the feasibility of using CLP as fresh fruit application.

The efficacy of 10x CLP extract to control B. cinerea and P. expansum was tested either at pH 2.0 or at pH 8.0; either as edible coating (in 80% ethanol with zein as carrier or in carnauba wax). ‘Packham’s Triumph’ pears or ‘Cripps Pink’ apples were inoculated with either an isolate of B. cinerea (Bot005) or an isolate of P. expansum (BD005). Fruit was treated either protectively (3 h before inoculation) or curatively (3 h after inoculation) with CLP (containing 80.7 mg/L fengycin and 1.1 mg/L iturin A); using fludioxonil as control. The treatments were compared in efficacy as thermofogging application, dip or spray application also comparing pH 2.0 and pH 8.0 in the formulation. The spray application further compared wax or zein as carrier. Disease incidence and severity were accessed on days 4, 6 and 8 after inoculation

CLP application as edible coating was most effective in reducing grey mould incidence in pears as a curative dip application (96% control, similar to fludioxonil in edible zein coating), while marginal efficacy was found for blue mould control on apples. Grey mould control was more effective at pH 2.0 (7.5 % incidence in dip), while pH 8.0 was more suitable for blue mould control (73 % incidence), although at pH 2.0, blue mould severity was reduced by 58%.

CLP crude extract applied at pH 2.0 is most effective (as dip) for grey mould control. Efficacy of CLP for blue mould control is not sufficiently applied as sole treatment and will have to be tested in other formulations or in combination with other alternative treatments, to increase efficacy.

Bacillus amyloliquefaciens CLPs have the potential to control postharvest pathogens when used in a zein edible coating as a carrier in the dipping application. Biofermentaion optimised to achieve consistent amounts of active compounds and at a larger scale is needed to get effective control with the metabolite CLP application on fruit. This study will contribute towards the development of new commercial products containing antagonist metabolites as active ingredient to control postharvest pathogens.