Biocontrol potential of Euphorbia paralias L. against phytoparasitic nematodes: A new botanical resource for sustainable nematode management

The eco-friendly management of phytoparasitic nematodes (PPNs) is really challenging. While several plant-based nematicides have shown promising results, many plant species -especially those from arid ecosystems- remain underexplored. Moreover, most studies have assessed the efficacy of botanical nematicides primarily in vitro , with limited data available from field conditions. The potential side effects on beneficial soil organisms, such as free-living nematodes, also remain poorly understood. In this study, we evaluated for the first time the nematicidal effects of Euphorbia paralias extracts on both plant-parasitic and free-living nematodes. Bioassays were conducted in vitro (using Meloidogyne spp.), in greenhouse conditions (on tomato plants), and under field conditions (in alfalfa crops). In the greenhouse experiments, we also assessed various plant growth parameters. In vitro tests showed that both aqueous and methanolic extracts of E. paralias exhibited significant nematicidal activity against Meloidogyne spp. juveniles (J2) and eggs, with 100 % mortality and hatching inhibition achieved at 2 % (w/v) for the aqueous extract and 0.1 % for the methanolic extract. In greenhouse trials, treatments with 3 % aqueous extract and 30 g/pot of dry powder significantly reduced Meloidogyne infestations, as indicated by decreases in root galling (-76.9 %), egg density per root system (-90.9 %), and total nematode population density (-97.4 %). However, dry powder doses exceeding 10 g per pot were phytotoxic to tomato plants. Under field conditions, the aqueous extract significantly reduced populations of Pratylenchus spp. and Xiphinema spp., while the dry powder showed a delayed but notable effect over time. The aqueous extract also stimulated bacterivorous nematodes, whereas fungivores and predators were less affected. Conversely, the dry powder, when applied at high doses (30 g/plant), was highly toxic to both predators and all phytoparasitic nematode taxa after six weeks. In conclusion, the strong nematicidal potential and natural abundance of Euphorbia paralias support its candidacy as a promising source for the development of new environmentally friendly nematicide formulations.