Phytotoxic Effects of Retentates Extracted from Olive Mill Wastewater Suggest a Path for Bioherbicide Development

Abstract

The aim of this study was to screen the phytotoxicity of different retentates concentrated in polyphenols and extracted from olive mill wastewater (OMW), namely, nano filtration retentate (RNF) and inverse osmosis retentate (ROI). The activity of both retentates was evaluated using bioassays on dry seeds (with concentrations of 0.0, 0.1, 0.5, 1.0, 5.0, and 10.0% and compared with CaCl2 solutions to evaluate the salinity effects), on germinated seeds (with concentrations of 0.0, 5.0, and 10.0%), and on the emergence of seedlings from the soil (with concentrations of 0.0, 5.0, and 10.0%). Three indicator plant species were used: Lepidium sativum L. (cress), Solanum lycopersicum L. (tomato), and Triticum turgidum subsp. durum Desf. (durum wheat). The results were expressed as the germination rate or emergence rate (GR or ER, respectively) and as the average germination time or average emergence time (AGT or AET, respectively) depending on the bioassays. Salinity showed a certain effect on the GR. Total or near-total inhibition of germination was obtained with the highest concentrations (5.0–10.0%). The dose of 1.0% of RNF and that of 0.5% of ROI caused delays in the germination of cress. The germination of tomato was delayed by RNF and ROI at concentrations of 0.5% and 1.0%. The AGT of durum wheat was not affected by RNF, but was slightly affected by ROI. The development of the seedlings was inhibited by both retentates. The results in the Petri dishes were also confirmed in pots. Retentates could be evaluated as a basis for the development of bioherbicides.

Different Weed Managements Influence the Seasonal Floristic Composition in a Super High-Density Olive Orchard

“… The prevalence of therophytes species recorded ( Table 1 ) (i.e., annual plants surviving harsh conditions as seeds, therefore, completing their life cycle from seed to seed and dying) and the prevalence of weeding techniques, namely inorganic and organic mulching, that physically impede seed germination as a consequence of shading and soil temperature variation [ 34 , 35 , 58 ]. Furthermore, organic mulching performs an allelochemical action on seed germination [ 34 , 43 , 44 , 45 ] mainly due to the bioactive fraction of organic materials, such as biophenols in the mulch [ 35 , 44 , 45 , 59 , 60 ]. Highest total infestation, weed characteristics and lowest infestation of all species when plots were managed with TNT, PEN and DOP on May 2007 is attributable to the deposition of seeds in the soil at the beginning of investigation: one of the most important sources of weeds is the seed bank of soil [ 61 ]; therefore, of the five treatments performed about two months before the first monitoring date (March 2007), only TNT, PEN and DOP significantly reduced the infestation of all therophytes species thanks to their mechanism of action.…”

“…The prevalence of therophytes species recorded (Table 1) (i.e., annual plants surviving harsh conditions as seeds, therefore, completing their life cycle from seed to seed and dying) and the prevalence of weeding techniques, namely inorganic and organic mulching, that physically impede seed germination as a consequence of shading and soil temperature variation [34,35,58]. Furthermore, organic mulching performs an allelochemical action on seed germination [34,[43][44][45] mainly due to the bioactive fraction of organic materials, such as biophenols in the mulch [35,44,45,59,60]. iii.…”

“…On the other hand, organic mulching involves the use of crop residues derived from agronomic practices or agro-industrial processes. Organic mulches simultaneously perform a physical and allelochemical action on seed germination [ 35 , 43 , 44 ]. Furthermore, the use of organic mulches in cropping systems has positive effects on soil fertility (physical, chemical and biological) and crop physiology [ 35 , 45 ] and should be considered as more sustainable in terms of environmental, agronomical and economical sustainability, especially in areas where they are produced in large quantities and in short periods of time and because the materials would otherwise be considered as waste.…”

Agronomic Impact and Phytotoxicity of Olive Mill Wastewater as a Biofertilizer on <i>Vicia faba</i> L.

“…On the other hand, at a concentration of 30%, the germination rate exhibits a significant decline to 73%. Many authors have also noted that high doses of OMW are phytotoxic and effectively prohibit seed germination (Enaime et al, 2020;Popolizio et al, 2022). This inhibition at elevated concentrations can be attributed to the toxic impact of salinity and the presence of polyphenols in OMW, the suppressive impacts of these phenolic compounds are more evident in terms of inhibiting root elongation as compared to seed germination (Hanafi et al, 2011;Bouknana et al, 2019).…”