Early diagnosis of graft union formation in grapevine using bioimpedance spectroscopy with a novel approach incorporating plant defense mechanisms

Grafting is essential for enhancing the functionality and productivity of horticultural crops; however, the success of conventional grafting is difficult to confirm visually and requires a long period. Therefore, there is a need for a rapid method to verify graft success at an early stage. In this study, bioimpedance spectroscopy (BIS) was employed to monitor changes in the electrical response of plant tissues in relation to scion viability with wound-induced defense mechanisms, and eventual graft success in grapevines ( Vitis spp.). These changes were understood in the context of physiological and structural alterations. ‘Kyoho’ grape scions were grafted onto ‘101–14’ rootstocks and maintained under controlled environmental conditions. Continuous BIS measurements were conducted at 30 min intervals over 32 days across a frequency range of 50 Hz to 1 MHz. Grafted and ungrafted groups exhibited distinct impedance signatures from 4 days post-grafting. The low-frequency (1 kHz) impedance increased in the grafted group, but decreased in the ungrafted group, with the high-frequency (100 kHz) phase angle showing similar patterns. This early divergence reflected the presence or absence of the scion's intrinsic healing capacity and viability, which served as an early indicator of final graft outcomes confirmed by dye uptake tests and shoot emergence at day 32. This study highlights the potential of BIS as a rapid tool for early assessment of eventual graft success by monitoring scion viability and defense responses, with a novel perspective on BIS for the plant defense mechanism, and can be utilized to reduce time and costs due to graft failure. Furthermore, BIS has the potential to be applied as a low-cost and simple method for graft monitoring in the future.