Impacts of different grapevine bench grafting methods on the xylem anatomy, hydraulic traits and wood necroses associated with young decline of grafted vines

Grapevine grafting is essential in viticulture, and bench grafting techniques have been developed to mechanize nursery processes and increase yields of viable cuttings. Bench grafting can affect the quality of propagation material and may have a role in young vine decline associated with grapevine trunk diseases. Some authors report that grafting can also influence leaf symptom development in Esca complex of diseases. This study assessed whether three bench grafting methods: omega graft, mechanical technique; whip and tongue graft, manual technique; or full cleft graft, semi-mechanical technique, affected these phenomena. The different methods were compared for their effects on anatomical development of grafting points and xylem function, considering two factors: cultivar (Cabernet Sauvignon, Glera or Teroldego) and scion/rootstock diameter (thin or large). Light microscopy observations of anatomical evolution were correlated with the grafting methods and the investigated varieties. Differences between cultivars and/or grafting methods were detected for areas of necroses on the grafted tissues. Cultivar differences in xylem parameters were also detected, while grafting type had no significant effects. However, graft type affected the intrinsic growth rate. These results confirm the potential for lesions and dysfunctionalities related to grafting method, which could induce decline of grafted vines in vineyards, due to the necrotic area detected on the grafted tissue