Mineralogical and geochemical signatures of healthy and KVDS-affected kiwifruit orchards: new insights into kiwifruit vine decline syndrome

Background and aims: Kiwifruit Vine Decline Syndrome (KVDS), first reported in Italy in 2012, is a severe disorder causing significant yield losses. This study investigates the mineralogical and geochemical characteristics of soils from two kiwifruit orchards in different areas of Lazio (Italy), exhibiting varying degrees of symptom severity (CTRL: no symptoms; INTER: moderate; KVDS: severe), to improve understanding of this syndrome. Methods: Soil samples were analyzed by X-ray Powder Diffraction (XRPD), thermal analysis (TG-DSC), X-ray Fluorescence (XRF), Transmission and Scanning Electron Microscopy with Energy-Dispersive Spectroscopy (TEM-EDS and SEM–EDS), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Chemico-physical parameters such as pH, electrical conductivity (EC), and loss on ignition (LOI) were measured and evaluated statistically through two-way ANOVA and cluster analysis. Results: The soils exhibited subacidic pH (6.0–6.7) and low to moderate electrical conductivity (EC ≈ 100–380 µS/cm), indicating moderately good natural fertility. Mineralogical and geochemical analyses reveal that KVDS is associated with profound alterations in soil composition. The decline manifests from two pedogenetic extremes: "immature" soils with interrupted weathering and instability (Site 1), or "hyper-mature" soils with intense halloysite formation, leading to waterlogging and salt stress (Site 2). In both cases, a fundamental deviation from a healthy mineralogical equilibrium may represent a key factor associated with vine decline. Conclusion: The findings reveal clear mineralogical and geochemical differences between KVDS-affected and healthy orchards. These results provide insights that may support the development of targeted soil and water management strategies to prevent the onset of KVDS and mitigate its severity.