Physiological responses to rootstocks vigor in Cherry: Why dwarfing is efficient?

This work investigates the different physiological responses induced by rootstock vigor on cherry trees, 'Black Star' grafted on semi-vigorous (CAB6P) and on semi-dwarfing (Gisela 6) rootstocks. Shoot and fruit growth were monitored during one season. The daily patterns of stem, leaf and fruit water potentials (Ψ) as well as leaf gas exchanges were assessed during post-veraison, while productivity and fruit quality were determined at harvest. Trees on Gisela 6 showed lower shoot growth rates and lower Ψstem and Ψfruit compared to trees on CAB6P, while no significant differences were found on Ψleaf, gas exchanges and fruit daily growth rates. As a consequence of the relative changes in Ψ, trees on Gisela 6 showed lower daily Ψ gradients between stem and leaves, which may have reduced shoot strength as a sink for water and carbohydrates and thus shoot growth, compared to CAB6P. On the contrary, a similar Ψ gradient between stem and fruit was recorded on Gisela 6, with likely positive consequences on fruit strength as a sink. This hypothesis is confirmed by the higher productivity and fruit soluble solid content found at harvest on trees grafted on Gisela 6. These results suggest that fruit on trees grafted on dwarfing rootstocks may increase their resource allocation toward shoots, thus leading to improved yield and fruit quality at harvest.