Grapevine (Vitis vinifera L. 'Pinotage') leaf stomatal size and density as modulated by different rootstocks and scion water status

Drought-tolerant rootstocks are expected to improve the grapevine response to water deficit by improving the water uptake and transport and by reducing the water loss in leaves by root-to-shoot signalling. Nevertheless, the mechanisms of rootstocks' tolerance to drought are not yet fully understood. The aims of this study were to evaluate the adaptation of Vitis sp. leaf stomata (density and size) to soil water deficit via interaction with different rootstocks known for their drought tolerance characteristics. Greenhouse trials were carried out in controlled ambient conditions. 'Pinotage' (Vitis vinifera L.) grafted onto two rootstocks (99Richter and 110Richter) were used. Half of the grapevines were subjected to severe water constraints. The other half were maintained well-watered. The results confirmed that one mechanism of 'Pinotage' leaf adaptation to water constraints was structural during leaf growth, with a reduction in pore size to reduce plant water loss. The transpiration rate of leaves was more related to stomatal size than density. Future studies with rootstocks with contrasting vigour inducing capacity and drought tolerance are needed in order to address the rootstock effect on leaf water status related to changes in leaf growth.