Effects of food additives on postharvest brown rot of stone fruit

Postharvest losses due to brown rot can be important, they are estimated between 5-10 % or more depending weather conditions. Since, in Europe, postharvest treatment are not allowed, the pathogen control depends only on fungicide spray programs in the field with insufficient results, especially when high humidity, warm temperatures and abundant rainfall prevail prior to harvest. In the past, alternative methods as: microbial antagonism, natural substances and substances Generally Recognized As Safe (GRAS) have been studied, with encouraging results, even if several of their key features are not still optimised. GRASs are food additive considered safe from Food Drug Administration (FDA) and are widely used for their antimicrobial, antifungl and inseticidial properties. The aims of the present work were to study the efficacy of several GRASs: calcium propionate (Ca-Prop), calcium oxide (Ca-Ox), potassium bicarbonate (K-Bic), potassium sorbate (K-Sorb) and sodium bicarbonate (Na-Bic) on conidial germination and mycelium growth in vitro and in vivo trials. Preliminary experiments showed that, in nectarine and peaches trials, Na-Bic was phytotoxic, at the minimum effective concentrations (30 g L-1) and K-Bic, Ca-Prop Ca-Ox were ineffective against Monilinia laxa. Only K-Sorb at 15 g L-1 was able to significantly reduce decay on natural infected fruit. A strong inhibitory effect on M. laxa poligacturonase was observed in a preliminary cup plate assay. Further studies are required to better understand the mechanism of action of K-Sorb against Monilinia spp., however the rule of enzymatic inhibition may be an important key in the pathogenic process.