Evaluation of the characteristics of rootstock hardwood cuttings on graft performance

Grafting success in grapevine nurseries considerably varies from year to year and between different batches of wood, and we still have little understanding about the causes of this variation. In order to identify them, rootstock wood batches (Vitis berlandieri × V. rupestris ‘110 Richter’) of different origins and growing conditions were characterized and used to determine grafting success rate. Ten batches from different mother vineyards were analysed; six batches from Spain and four from France. To characterize the wood, the presence of viruses (GFkV, GFLV, GLRaV1, and GLRaV3) and pathogens associated with fungal trunk diseases (Petri and Black foot diseases, and Botryosphaeria dieback) were tested. Furthermore, wood was histologically characterized by measuring tissue size (pith, xylem, and phloem), the number of xylem vessels, and xylem conductivity. The content of metabolites (starch, sucrose, glucose, fructose, and proteins), macronutrients (N, Na, K, Ca, S, Mg, and P), micronutrients (Bo, Zn, Mn, Fe, Cu, and Al) and isotopes (δ¹³C and δ¹⁵N) was also determined. The only pathogen detected was Cadophora luteo-olivacea in two batches. Main differences found among batches were the presence of large vessels, whose diameter ranged from 240 to 320 µm, resulting in a significantly higher xylem specific conductivity, and for the metabolites content, results showed strong variation across the different batches. After uprooting, grafting success rate was recorded and related with the metabolite, nutrient, and isotope contents. A positive correlation of grafting success with the parameters of water stress (δ¹³C), nitrogen assimilation (δ¹⁵N), and the percentage of large vessels (200-280 µm) was observed. Therefore, results showed that multiple factors affect the grafting success rate and highlight the need for further research on the topic.