Grapevine rootstock effects on scion biomass are not associated with large modifications of primary shoot growth under nonlimiting conditions in the first year of growth

In grapevine (Vitis vinifera L.), rootstocks are known to alter scion development by modifying stem weight and yield. The aim of this work was to evaluate the contribution of primary growth to the rootstock effects on scion biomass. The shoot growth of Vitis vinifera cv. Cabernet Sauvignon N autografted and grafted onto Vitis riparia cv. Riparia Gloire de Montpellier and Vitis berlandieri x V. rupestris cv. 1103 Paulsen was studied in young plants grown in pots trained to one stem in two experiments. Stem elongation and phytomer emergence were studied from grafting until the end of the growth season. The elongation of the Cabernet Sauvignon N leaves, tendrils and internodes of each phytomer along the stem was fitted using sigmoid curves. The rootstocks studied slightly altered the growth dynamics of the leaves, internodes and tendrils of the scion. This is the first study to examine the effect of rootstocks on shoot growth dynamics in any species. The alterations in primary growth were small, suggesting that rootstocks may alter scion biomass principally by modifying secondary growth.