POSTHARVEST CONTROL OF MONILINIA LAXA AND RHIZOPUS STOLONIFER IN STONE FRUIT BY PERACETIC ACID

Peracetic acid (PAA) treatment of stone fruits (sweet cherry, apricot, peache and nectarine) reduced the incidence of brown rot caused by Monilinia laxa and soft rot caused by Rhizopus stolonifer. The efficacy of the treatment depended on the length of time. Fruit, neither wounded nor inoculated and dipped for 1 min in a 125 mg L-1 PAA solution, showed a significant reduction of Monilinia rots with respect to control. Significant inhibition was also observed on fruit wounded and inoculated with R. stolonifer and treated for 1 min with 250 mg L-1 PAA solution. Preliminary experiments were also conducted to determine the effects of sodium bicarbonate (SBC) sodium propionate (Na-Pro) and potassium sorbate (K-Sorb), substances generally regarded as safe (GRAS) against pathogens. Phytotoxic effects appeared on fruit treated with SBC at the minimum effective concentration (3%). Only K-Sorb at 1.5% was able to significantly reduce Monilinia infections in sweet cherries (61.6%), apricots (78%) and nectarines (31.8%) with respect to control, without any visible damage on the skin. Similar results were obtained on apricot wounded and inoculated with three different concentrations (102, 103 and 104 conidia ml-1) of R. stolonifer. PAA and K-Sorb showed the same efficacy on apricots and nectarines against M. laxa. K-Sorb was less effective than PAA on nectarines and peaches inoculated with R. stolonifer. Fruit hydro-refrigeration significantly reduced the incidence of brown rot in Nero I and Van sweet cherries; disease control was improved by addition of PAA (125 mg L-1) in cold water. PAA efficacy on pre-existing infections can be very useful to control stone fruit diseases that can spread during shipping and marketing.