The efficacy of red onion peel methanol extract to prevent dry rot in potato tubers caused by Fusarium sambu-cinum was investigated. At 20 mg mL-1, the methanol extract caused a great decrease in the fungal growth and spore germination by 86.3 %, and 91.2 %, respectively. Also, the dry rot control efficacy in potato slices inoc-ulated with F. sambucinum reached 91.8 % at the same concentration. The treatment with methanol extract significantly increased the total phenolics to 0.31 g kg -1 compared with the control (0.19 g kg -1) in potato slices on the fourth day of the storage period as well as the increase in the level of total flavonoids. The relative leakage rate was 46.3 % in treated potato tuber slices compared to the control by 76.5 % and MDA content was much lower in slices treated compared with control slices during four days of storage. The methanol extract enhanced the activity of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO), catalase (CAT), and peroxidase (POD) in potato slices throughout the experiment. The major compounds in the methanol extract were the flavonoids rutin, quercetin triglucoside, ferulic acid, quercetin diglucoside, quercetin monoglucoside, iso-rhamnetin glucoside, quercetin, kaempferol, and isorhamnetin using HPLC-UV/DAD, QTOF, and NMR spectra (1H NMR, APT, HSQC, COSY, HMBC, and NOESY).
