Detecting spots of garden strawberry by impedance spectroscopy method

The study was conducted to identify eight informative parameters of the electrical impedance of strawberry leaf tissue: active and reactive resistance in series and parallel circuits of the measurement object electrical model, phase shift, capacitance, loss tangent, impedance module. These parameters are associated with the action of fungi pathogens of garden strawberry spots Ramularia tulasnei Sass, Marssonina potentillae (Desm), Dendrophoma obscurans (Ell. & Ev.) Anderson). Diagnosis of diseases was carried out by visual analysis of symptoms and microscopic analysis of the sporulation of fungi pathogens. The study was carried out using a precision impedance analyzer WK 6505B in accordance with the developed technique. The bio-impedance parameters of the strawberry leaf tissue were measured using sensor electrodes placed on the upper side of the leaf with a constant clamping force. Each parameter of the tissue bio-impedance on the leaf surface was measured when electrodes were installed to the right and left of the central leaf vein. To reduce the contact resistance between the electrodes and the leaf surface, the electrodes were lubricated with a special electrode gel. There were 2624 dependences obtained of the bio-impedance parameters of healthy leaves and the ones affected with white, brown, and angular spots of three varieties of garden strawberry (Eliani, Tanyusha, and Darenka). The variance analysis of the average values of the data revealed that the most informative part of the changes in all parameters lies in the low-frequency region of α-dispersion of bio-impedance: from 20 Hz to 10 kHz. It is proposed to use reactive impedance measured in the low-frequency region of α-dispersion of bioimpedance as the main informative parameter of bio-impedance for detecting spots. With this reactive impedance, extreme values of its change appear for healthy leaves of garden strawberries and the diseased ones. The results of the research will be used to create a device for the early diagnosis of spots of wild strawberries.