Sensitivity of Pectobacterium carotovorum to hydroxytyrosol-rich extracts and their effect on the development of soft rot in potato tubers during storage

• Pectobacterium carotovorum is the most devastating potato disease worldwide.
• All potato-seed treatments are fungicides and can not affect soft-rotting Enterobacteria.
• We demonstrated hydroxytyrosol-rich extract (HRE) as natural disinfectant of seeds.
• HRE is a potential anti-P. carotovorum applicable in the post-harvest phase.

A hydroxytyrosol-rich olive mill wastewater (HROMW) (29.3% weight:dry weight) and a hydroxytyrosol-rich extract (HRE) (52.7% weight:dry weight) were prepared from the fresh olive mill wastewater (OMW) using hydrolysis and post-hydrolysis purification processes. The minimal bactericidal concentrations of HROMW and HRE against Pectobacterium carotovorum subsp. carotovorum were 72 and 40 g L−1, respectively. According to the European standard method (EN 1276: 1997), HROMW and HRE showed powerful disinfectant properties and reduced the viability of P. carotovorum by more than 5 log units after a contact time of 5 min at 2% dry weight:volume. Curative and preventive controls of potato soft rot were obtained by treatment of tubers with HROMW or HRE 3 days before or 3 days after their infection with P. carotovorum, respectively. The soft rot development during potato tuber storage was significantly reduced by treatment with HRE. This extract could be used in eco-friendly strategies of post-harvest disease control and could substitute for chemical pesticides.