Evaluation of graft success of grapevine after incubation room by means of thermographic, electrical and mechanical techniques

Grafting is an important technique for getting good yields in plant multiplication. Understanding the success of the graft after the incubation stage is important to the evaluation of the suitable grafting for the open field (nursery). Successful grafting in vines requires the development of a functional vascular system between the scion and the rootstock. The graft compatibility and its augmentation depend upon various natural factors like environment, soil conditions and protective measures. The present study examines the capability of thermographic, mechanical and electrical techniques to assess the graft quality and success after the incubation stage. The trial was carried out at Vivai Mannone, (Petrosino, Western Sicily, 37°42'26.28''N - 12°29'09.57''E). After the different tests, various grafting combinations were planted in the nursery and followed for the vegetative season. Before the evaluation procedure was performed graft unions have been subjected to a moderate heating from ambient temperature, then the thermal transient toward ambient temperature was monitored by means of a thermal imaging camera. As far as the electrical testing procedure was concerned, a sinusoidal voltage was applied through the grafts-cuttings, and the voltage attenuation at different points at increasing distances from the source was measured by an oscilloscope. The mechanical strength of the graft undergoing a controlled rate flexural loading was monitored by a PC remote controlled digital dynamometer. Experimental results show that we were able to distinguish the successful grafting only with the thermographic test. Moreover, this technique was the only non-destructive test from which it was possible to derive quantitative parameters, useful to provide successful nursery forecast. Engraftment results detected at the nursery showed a 15% error in forecast based on the proposed thermal image method, which is a satisfactory value for a feasibility study.