Use of commercial fertilizers in an IPDM protocol to mitigate Olive Quick Decline Syndrome caused by Xylella fastidiosa subsp. pauca in Southern Italy

Management of Xylella fastidiosa subsp. pauca (Xfp) presents significant challenges due to the lack of genetic resistance in major crops, pathogen variability and resistance development against the main antimicrobial compounds, and the lack of effective chemical compounds for control. Traditional bactericides in the EU are restricted, and copper-based products are increasingly limited due to environmental impacts. In this study the antibacterial side effects of some commercial fertilizers against Xfp were evaluated. These products, containing metal ions (mainly copper and/or zinc) complexed with phosphites and bioavailable silicon, show antimicrobial and bactericidal activities in vitro which suggest their possible use to control the pathogen, as well as enhanced plant resistance to biotic and abiotic stresses. Greenhouse and open field trials showed that they can significantly reduce disease severity and pathogen population, thus improving fruit yield. The integrated pest and disease management (IPDM) strategy, which combines these treatments with agronomic and phytosanitary vector-control measures, leads to a reduction of disease symptoms in treated plants compared to untreated ones. These findings highlight the potential of systemic fertilizers to mitigate Xfp symptoms by providing antimicrobial collateral effects and probably enhance plant defenses, since similar compounds are known to be plant defense inducers in other pathosystems. Therefore, these products offer a sustainable solution for managing plant pathogenic bacteria and improving crop health and yield. This approach is crucial for the sustainability of olive production in Xf-affected areas. However, further research is needed to optimize these strategies for long-term effectiveness under field conditions. Overall, the results emphasize the value of the collateral effects of some mineral fertilizers in a comprehensive strategy aimed at mitigating the symptoms of Xfp and safeguarding the agricultural productivity as well as the invaluable heritage of centuries-old Apulian olive trees.