Combined effect of virus infection and water stress on water flow and water economy in grapevines.

Water limitation is one of the major threats affecting grapevine production. Thus, improving water-use efficiency (WUE) is crucial for a sustainable viticulture industry in Mediterranean regions. Under field conditions, water stress (WS) is often combined with viral infections as those are present in major grape-growing areas worldwide. Grapevine leafroll-associated virus 3 (GLRaV-3) is one of the most important viruses affecting grapevines. Indeed, the optimization of water use in a real context of virus infection is an important topic that needs to be understood. In this work, we have focused our attention on determining the interaction of biotic and abiotic stresses on WUE and hydraulic conductance (K ) parameters in two white grapevine cultivars (Malvasia de Banyalbufar and Giró Ros). Under well-watered (WW) conditions, virus infection provokes a strong reduction (P < 0.001) in K in both cultivars; however, K was only reduced in Malvasia de Banyalbufar. Moreover, the presence of virus also reduced whole-plant hydraulic conductance (K ) in 2013 and 2014 for Malvasia de Banyalbufar and in 2014 for Giró Ros. Thus, the effect of virus infection on water flow might explain the imposed stomatal limitation. Under WS conditions, the virus effect on K was negligible, because of the bigger effect of WS than virus infection. Whole-plant WUE (WUE ) was not affected by the presence of virus neither under WW nor under WS conditions, indicating that plants may adjust their physiology to counteract the virus infection by maintaining a tight stomatal control and by sustaining a balanced carbon change.