Effects of graft quality on growth and grapevine-water relations

Abstract

Climate change is challenging viticulture worldwide compromising its sustainability due to warmer temperatures and the increased frequency of extreme events. Grafting Vitis vinifera L. (traditional cultivars for wine production) onto North American grapevine species or hybrids is routinely used in most grape growing areas accounting for about the 80% of vineyards globally. Grapevine grafting started at the end of the 19th century to combat phylloxera (Daktulosphaira vitifoliae), since many of the American Vitis species are tolerant to this soil born pest. Decline of vineyard longevity might be partially explained by a decline in grafting quality in the nurseries. Omega grafting stands out as the most popular grafting method given its higher success rate in nurseries. However, the high pace of the grafting production leads to a poor-quality union of the graft point, with a smaller contact surface and presumably a worse connection area, compromising the phloem and xylem formation. Thus, we hypothesized that performing an omega graft of higher or lower technical quality could have implications on grapevine physiology, especially in terms of water relations. We identified two levels of technical quality: CA, completely aligned scion and rootstock cuttings where the scion and the cane had the same diameter and PA, partially aligned scion and rootstock cuttings where the scion and rootstock had different diameters. Results showed that CA plants had a higher rate of vegetative growth and higher gas exchange performance in terms of transpiration and canopy stomatal conductance. These trends were not explained by increased hydraulic conductivity at the scion level, thus, results suggested an effect of the grafting quality on the phloem formation. Therefore, this study highlights the relevance of exploring the effect of the grafting quality on the grapevine water relations to identify how the changes in plant performance could help on achieving resilient plants to water stress or drought.