Root Exudates Metabolic Profiling Confirms Distinct Defense Mechanisms Between Cultivars and Treatments with Beneficial Microorganisms and Phosphonate Salts Against Verticillium Wilt in Olive Trees

Abstract

Root exudates play a key role in the life cycle of Verticillium dahliae, the causal agent of Verticillium wilt diseases, because they induce microsclerotia germination to initiate plant infection through the roots. In olive plants, the genotype and the application of biological control agents (BCAs) or phosphonate salts influence the ability of root exudates to decrease V. dahliae viability. Understanding the chemical composition of root exudates could provide new insights into the mechanisms of olive plant defense against V. dahliae. Therefore, the main goal of this study was to analyze the metabolomic profiles of root exudates collected from the olive cultivars Arbequina, Frantoio, and Picual subjected to treatment with BCAs ( Aureobasidium pullulans AP08, Bacillus amyloliquefaciens PAB-024) or phosphonate salts (copper phosphite, potassium phosphite). These treatments were selected due to their effectiveness as inducers of resistance against Verticillium wilt in olive plants. Our metabolomic analysis revealed that the olive cultivars exhibited differences in root exudates, which could be related to the different degrees of susceptibility to V. dahliae. The composition of root exudates also changed with the application of BCAs or phosphonate fertilizer, highlighting the complex and dynamic nature of the interactions between olive cultivars and treatments preventing V. dahliae infections. Thus, the identification of genotype-specific metabolic changes and specific metabolites induced by these treatments emphasizes the potential of resistance inducers for enhancing plant defense and promoting the growth of beneficial microorganisms.