Valorization of Posidonia oceanica Biomass Extract as an Elicitor to Mitigate Aphid-Induced Stress in Sweet Pepper Plants

The increased restrictions on the use of synthetic pesticides have made the application of substances that induce plant defense mechanisms an effective alternative for protecting plants while minimizing environmental and health risks. One of the most damaging pests for sweet pepper production is the infection by the green peach aphid. This study determined the best extraction method from <i>Posidonia oceanica</i> waste and evaluated its efficacy against <i>Myzus persicae</i> (Sulzer) aphid-induced stress. In particular, the foliar application of the extract at two different doses was investigated on sweet pepper plants. The results showed that both doses decreased the contents of H₂O₂ (40.8% and 56.3%, respectively) and malonaldehyde (31.1% and 39.9%, respectively) in plant tissue, indicating a reduction in oxidative stress. Additionally, these elicitor extracts were effective in maintaining cell membrane integrity and photosynthetic activity. This resulted in an increase in fresh and dry weight, as well as in cellulose and hemicellulose concentration. In conclusion, <i>Posidonia oceanica</i> extracts are a promising organic farming-treatment to fight against aphid pest and its ability to stimulate plant self-defense mechanisms.