Interactive effects of grapevine leafroll-associated virus 3 (GLRaV-3) and water stress on the physiology of Vitis vinifera L. cv. Malvasia de Banyalbufar and Giro-Ros.

Among several biotic and abiotic stress combinations, interaction between drought and pathogen is one of the most studied combinations in some crops but still not in grapevine. In the present work, we focused on the interaction effects of biotic (GLRaV-3) and abiotic (drought) stresses on grapevine photosynthetic metabolism on two cultivars (cvs. 'Malvasia de Banyalbufar and Giro-Ros'). Non-infected and GLRaV-3 infected potted plants were compared under water stress conditions (WS) and well-watered (WW) conditions. Under WW condition, the results showed that photosynthesis (AN) in both cultivars was decreased by the presence of GLRaV-3. The stomatal conductance (gs) was the main factor for decreasing AN in Malvasia, meanwhile reductions in Giro-Ros were closely related to decreases in gm. The observed differences in gm between both cultivars might result from variation in their leaf anatomical, Giro-Ros having higher values of gm and leaf porosity (in all treatments). Moderate water deficit resulted in a closure of stomata and a decrease in gm accompanied by a decrease in AN in both cultivars. The maximum velocity of carboxylation (Vcmax) and electron transport rate (Jmax) were also reduced under water stress. Moreover, the combined stress resulted in a reduction of most physiological parameters compared to healthy irrigated plants. However, no considerable differences were found between non-infected and virus infected (GLRaV-3) plants under water stress. Most of the results could be explained by the difference of virus concentration between cultivars and treatments.