Photosynthesis of Ungrafted and Grafted Grapevines: Effects of Rootstock Genotype and Plant Age

¹ Bundesanstalt für Züchtungsforschung an Kulturpflanzen, Institut für Rebenzüchtung Geilweilerhof, D-76833 Siebeldingen, Germany.

Measurements of the daily maximum rate of photosynthesis (A_max) of leaves of ungrafted and grafted field-grown grapevine varieties indicated higher rates in vines grafted to the rootstock Kober 5BB. While higher rates of A_max in grafted Orion and Gf.Ga-54-14 vines were linked to both higher values of the carboxylation efficiency and of stomatal conductance in Riesling and Gf.Ga-47-42 vines, it was associated with increases of the carboxylation efficiency but not with stomatal conductance. This led to distinctly higher values of the water use efficiency of grafted Riesling and Gf.Ga-47-42 vines. Similar results were obtained using four-year-old potted vines; Riesling grafted to Kober 5BB had significantly higher rates of photosynthesis but similar rates of stomatal conductance compared to ungrafted Riesling or Riesling grafted to Riesling. Within the first four years the rate of photosynthesis of leaves of ungrafted and grafted Riesling vines increased more than twofold. It is suggested that grafting vines to appropriate rootstock varieties which favor the increase of the carboxylation efficiency of scion leaves may help to improve drought resistance by raising the water use efficiency.

Key words: Vitis, photosynthesis, stomatal conductance, water use efficiency, drought resistance, rootstock

Submitted on July 12, 1993