Search Results (4)

Secondary metabolites in olive (Olea europaea L.) leaves constitute a complex framework wherein phenylpropanoids, terpenoids, and secoiridoids in particular, serve as major contributors to olive plant resilience. Silicon (Si) stands as a mediator of defense mechanisms in plants, enhancing their protective responses and adaptability. A field trial on one-year-old plantlets of two metabolically distinct olive genotypes was conducted to investigate the effects of foliar-applied Si on the phytochemical profiles of locally treated leaves. Silicon’s systemic effects in juvenile leaves were also appraised. We accounted for intervarietal differences in nutrient uptake and conducted in situ measurements of physiological indices. The peak of the summer season and the onset of autumn were chosen as the two sampling time points. Intense summer conditions prompted metabolic adjustments that resulted in phytochemical profiles unique to each cultivar. These profiles were further significantly altered by Si while remaining genotype-specific, with substantial increases in prominent compounds like oleuropein (105% and 252%) and verbascoside (62% and 126%), depending on the genotype. As the pressure from environmental factors eased, the differences in Si-mediated phytochemical responses emerged. Silicon had a limited effect on the phytochemical profile of the resilient cultivar which acquired a metabolic steady-state, while it significantly altered the profile of its metabolically more versatile counterpart, resulting with a progressive increase in its oleuropein (37%) and verbascoside (26%) levels. These effects extended to untreated, juvenile leaves as well. While effective in altering and improving the phytochemical composition of olive leaves, Si acted in a manner that adhered to each genotype’s metabolic foundation. The intensity of environmental constraints, along with each cultivar’s inherent sensitivity to them, seems to be tied to silicon’s capacity to mediate significant phytochemical alterations. The extent of silicon’s prophylactic function may therefore be dependent on a genotype’s metabolic foundation and overall sensitivity, and as such it seems inseparable from stress and its intensity. Full article

Verticillium wilt of olive, caused by Verticillium dahliae Kleb., is a serious disease with no highly effective control methods currently available. Consequently, biological control strategies are being explored as viable and environmentally friendly alternatives. A natural recovery phenomenon has been observed in certain olive varieties following infection by low-virulence isolates of the pathogen, likely due to plant resistance mechanisms that may enhance defense against more virulent isolates. Based on these findings, a study was conducted to determine whether plants that had recovered from infection by a low-virulence isolate could exhibit increased resistance to highly virulent isolates. ‘Picual’ plants were first inoculated with a non-defoliating isolate, followed by inoculation with a defoliating isolate at different time intervals. The results demonstrate that prior infection with a non-defoliating isolate reduced disease severity caused by a defoliating isolate, particularly in susceptible cultivars like ‘Picual’. Treated plants exhibited slower disease progression and no mortality, whereas untreated plants developed severe symptoms and showed high mortality rates. A minimum interval of four months between inoculations with isolates of different virulence was crucial for achieving a significant reduction in disease severity. While this methodology has proven effective, further research is needed to elucidate the underlying mechanisms and identify additional biocontrol agents to enhance disease management strategies. Full article

Verticillium wilt of olive (VWO), caused by Verticillium dahliae (Vd), represents a significant threat to olive cultivation, particularly to the Moroccan cultivar “Picholine Marocaine”, by reducing yield, tree survival, and overall productivity. Current chemical and cultural control strategies provide limited efficacy, highlighting the need for alternative approaches such as biological control. This study investigated the potential of Rhizophagus irregularis (RI) as a biological agent to mitigate VWO over a 10-month period following V. dahliae inoculation. Disease severity, incidence, and defoliation rate as well as oxidant stress markers, antioxidant enzyme activities, and the phenolic pathway were evaluated in a greenhouse experiment. Our results showed that R. irregularis significantly reduced (p < 0.05) disease severity and incidence by about 31% and 26%, respectively, and decreased defoliation rates by 35% in RI-infected plants (RIV). The presence of R. irregularis triggered enhanced antioxidant enzyme activities (e.g., superoxide dismutase, catalase, and polyphenoloxidase), increased lignin deposition, elevated phenylalanine ammonia-lyase activity, and increased total phenol content in olive tissues. These biochemical and structural changes reduced lipid peroxidation, oxidative stress, and physiological damage, resulting in delayed disease progression. Enhanced accumulation of lignin and total phenolic compounds, particularly in aboveground tissues, was observed. This likely reinforced cell walls and enhanced resistance to pathogen infection. This study demonstrates that R. irregularis offers a promising biocontrol agent for combating soil-borne diseases in olives and other susceptible crops by mitigating VWO, boosting antioxidant defenses, and modulating the phenolic pathway with tissue-specific responses. Full article

Xylella fastidiosa subsp. pauca, is a bacterial phytopathogen associated with the “olive quick decline syndrome” (OQDS) causing severe economic losses to olive groves in Salento area (Apulia, Italy). In a previous work, we analyzed by ¹H-NMR the metabolic pattern of naturally infected Ogliarola salentina and Cellina di Nardò susceptible cultivars untreated and treated with a zinc-copper citric acid biocomplex and we observed the treatment related variation of the disease biomarker quinic acid. In this study, we focused also on the Leccino cultivar, known to exhibit tolerance to the disease progression. The ¹H-NMR-based metabolomic approach was applied with the aim to characterize the overall metabolism of tolerant Leccino in comparison with the susceptible cultivars Ogliarola salentina and Cellina di Nardò under periodic mid-term treatment. In particular, we studied the leaf extract molecular patterns of naturally infected trees untreated and treated with the biocomplex. The metabolic Leccino profiles were analyzed for the first time and compared with those exhibited by the susceptible Cellina di Nardò and Ogliarola salentina cultivars. The study highlighted a specificity in the metabolic response of the tolerant Leccino compared to susceptible cultivars. These differences provide useful information to describe the defensive mechanisms underlying the change of metabolites as a response to the infection, and the occurrence of different levels of disease, season and treatment effects for olive cultivars. Full article