Stress Fingerprints of Phyllocoptruta oleivora Infestation: from Pomology to Polymethoxyflavones in Citrus sinensis.

Citrus rust mite (Phyllocoptruta oleivora Ashmead) (Acari: Eriophyidae) (CRM) is a significant biotic stressor affecting citrus fruit quality by damaging the peel and inducing physiological and chemical alterations. This study explores the dual impact of mite infestation on the pomological traits and peel phytochemistry of Citrus sinensis (orange), with a focus on polymethoxyflavones (PMFs), a class of secondary metabolites associated with plant defense. Oranges with varying levels of visible CRM injury (INJ1 to INJ3) were compared to uninjured controls. Morphological analysis revealed significant reductions in fruit weight, size, peel thickness, and juice content with increasing injury severity, while total soluble solids (TSS) increased moderately. Phytochemical profiling of peel extracts obtained by subcritical water extraction and supercritical CO₂ extraction indicated a notable rise in PMFs content-from 3.8% in control samples to 9.5% in the most severely injured group. These biochemical and morphological changes together represent distinct stress fingerprints associated with CRM. Our results demonstrate that CRM infestation elicits a multifaceted plant response, simultaneously impairing physical fruit traits and activating secondary metabolism. The accumulation of PMFs in damaged peel suggests an induced defense mechanism that may serve as a biochemical marker of herbivore stress. These findings underscore the importance of integrating chemical ecology perspectives into citrus pest management and provide new insights into host-arthropod interactions in perennial crop systems.