Monitoring Rose Black Spot Disease Using Electrical Impedance Spectroscopy

Rosa hybrida is a globally important ornamental species, but its economic and aesthetic value is often compromised by rose black spot disease (Diplocarpon rosae). Effective monitoring and early detection are essential for disease management. This study investigated physiological and biophysical responses to infection in a resistant cultivar (‘Carefree Wonder’) and a susceptible cultivar (‘Red Cap’) using electrical impedance spectroscopy (EIS), biochemical assays, and ultrastructural analysis. Key EIS parameters (ri, re, τ), reducing sugar and free proline content, chitinase and β-1,3-glucanase activities, and chloroplast ultrastructure were monitored. The results showed that ‘Carefree Wonder’ had a higher initial EIS arc magnitude and osmolyte levels than ‘Red Cap’. Following infection, ‘Red Cap’ displayed earlier and more pronounced increases in EIS arc magnitude, while ‘Carefree Wonder’ responded more gradually. Reducing sugar and proline levels increased in both cultivars, with earlier accumulation in the resistant cultivar. Notably, extracellular resistivity (re) exhibited strong positive correlations with reducing sugar (R2 = 0.479), free proline (R2 = 0.399), chitinase (R2 = 0.399), and β-1,3-glucanase activities (R2 = 0.401). These findings highlight re as the most reliable EIS-derived indicator for early, non-destructive detection of rose black spot resistance. This study supports the potential of EIS for rapid disease diagnostics in rose breeding and cultivation.