Different grapevine bench grafting methods affect wood necrosis associated with young declines of grafted vines

Grapevine grafting has become an essential practice in viticulture and over the years various bench grafting techniques have evolved to mechanize the nursery process and to increase the yield in number of viable cuttings. Bench grafting is a fundamental nursery practice that affects the quality of propagation material also in young decline associated to grapevine trunk diseases, and has been recently reported to influence leaf symptoms development associated to diseases of Esca complex. The present study aimed to investigate how three bench grafting methods (omega graft as mechanical technique, whip and tongue graft as manual technique and full cleft graft as semi-mechanical technique) can influence these phenomena, comparing their effect on anatomical development of the grafting point and on functionality of vascular tissue, also considering two factors: cultivar (Cabernet Sauvignon, Glera and Teroldego) and scion/rootstock diameter (thin and large). Light microscopy observations on the anatomical evolution were correlated with the grafting methods and the investigated arieties. Significant differences between cultivars and/or graft type were also detected in terms of necrotic area on the grafted tissues. Statistical analysis of the grapevine vessels suggested differences in xylem parameters between cultivars while graft type had no have significant effects. On the other hand, the intrinsic growth rate was significantly affected by the graft type. The results confirm the potential incidence of lesions and dysfunctionalities correlated with the grafting method applied, which can potentially induce grafted vine declines in vineyard as a result of the necrotic area detected on the grafted tissues.