Postharvest control of citrus green mold caused by Penicillium digitatum using a LAB-activated lemon-peel-derived formulation

Green mold, caused by Penicillium digitatum, is the most damaging postharvest citrus fruit disease. Conventionally, it is managed with synthetic fungicides. This study evaluated a cell-free, non-viable, lactic acid bacteria (LAB)-activated lemon peel-derived formulation (LM + LAB), produced by fermenting a lemon peel-based medium with Lactiplantibacillus plantarum N3B2, under two application scenarios. LM + LAB was compared with imazalil (standard synthetic fungicide), the yeast Candida oleophila strain O, a potassium phosphite-based formulation, phosphorous acid, and an untreated control. Sweet orange fruit were treated either before inoculation or 4 h after inoculation with P. digitatum. Fruit were stored for 7 days at 6 °C and then at 18 °C until 14 days post-inoculation. Disease incidence was assessed at 7, 10, and 14 days, sporulation reduction at 14 days, and fruit quality throughout storage. Imazalil provided the most effective control. LM + LAB significantly reduced disease incidence under both application scenarios. At 14 days, incidence was reduced from 78% to 38% when LM + LAB was applied before inoculation and from 79% to 15% when it was applied 4 h after inoculation. Sporulation was reduced by 43% and 64%, respectively. When applied post-inoculation, LM + LAB was as effective as imazalil and C. oleophila in reducing disease incidence and suppressed sporulation more effectively than the yeast. Potassium phosphite and phosphorous acid were the least effective substances. None of the treatments caused weight loss or significantly affected firmness, total soluble solids, juice pH, or titratable acidity of fruit. Results show LM + LAB is a promising natural product for management of citrus green mold.