Carob and pomegranate extracts enhance plant defence mechanisms against olive anthracnose through antioxidant activity and phenolic compounds production

Abstract

Olive anthracnose (OA), caused by Colletotrichum species, is one of the most economically damaging disease in olive sector. This study was focused to identify sustainable control alternatives by evaluating the effect of pomegranate and carob extracts against OA and elucidating their mode of action. In vitro assays on mycelial growth, conidial production, and germination, and appressoria formation of C. godetiae and C. nymphaeae were performed. Neither extract significantly inhibited mycelial growth, while both reduced reproductive structures formation of the pathogens. Bioassays on detached and attached olive fruits in plants of cv. Arbequina, treated with extracts and/or inoculated with C. godetiae were conducted to evaluate the effect of the extracts on disease progression. Despite of the limited effect of the extracts on reducing disease progression in detached fruit, curative applications were more effective than preventive ones. Carob extract was more effective than pomegranate extract in reducing the disease incidence progression in attached fruit in planta. The resistance-inducing effect of plant extracts was evaluated by quantifying of H2O2 and phenolic compounds production in olive leaves at 0, 3, 7 and 24 h after inoculation with C. godetiae. Both extracts increased these parameters in the inoculated plants, with carob extract triggering an earlier activation and promoting a greater diversity of phenolic compounds accumulation. These findings reveals that these two extracts act as resistance inducers through different effective defence pathways, with carob extract standing out as a promising bioprotector against OA. These results open new possibilities for environmentally friendly management of OA using plant extracts.