Potential of hydroxytyrosol-rich composition from olive mill wastewater as a natural disinfectant and its effect on seeds vigour response

Hydroxytyrosol-rich olive mill wastewater (HROMW) and hydroxytyrosol-rich composition (HRC) were prepared from olive mill wastewater using hydrolysis and post-hydrolysis purification processes. The HROMW and HRC showed powerful bactericidal and fungicidal activities against phytopathogens, and their minimal inhibition concentrations for fungi and bacteria were 7.18-57.4mgl⁻¹ and 7.18-14.4mgl⁻¹, respectively. After 5min of contact time, the disinfectant properties of the HROMW and HRC added at concentrations of 1.25% (dw/v) allowed for a reduction in bacterial viability by greater than 5 log units. However, a higher concentration of 1.5-3% (dw/v) or a longer contact time of 30min were needed to achieve values for fungal viability reduction that were higher than the 4 log units recommended by EN 1275 [EN 1275 (1997a). Chemical disinfectants and antiseptics. Basic fungicidial activity. Test method and requirements (phase 1)]. HROMW and HRC were less effective with the most ubiquitous fungi, Fusarium spp., which needed 10% dw/v. The addition of HRC at 10% (dw/v) showed that the composition was a potent exogenous enhancer of growth that stimulated the seedling vigour of tomato and muskmelon, according to the conventional agronomic parameters for seed vigour. Compared to the control, the germination percentage, shoot weight, shoot height, and root length were all significantly enhanced in the HRC-treated seed plants. HRC was found to have effective disinfectant properties against seed-borne diseases. In treated seeds, the composition had significant effects on the control of damping-off disease groups at the pre-germination stage. HRC was also equally effective in the control of root rot diseases caused by Fusarium sambucinum and Alternaria solani as well as of wilts and even bacterial seed-borne pathogens. HROMW was also found to be as effective as HRC in terms of its efficacy against the three seed-borne diseases mentioned above.