Ecophysiological responses of grapevine rootstocks to water deficit

The use of rootstocks tolerant to soil water deficit is an in-teresting strategy to face the challenges posed by limited water availability. Currently, several nurseries are breeding new genotypes aiming to improve the water stress tolerance of grapevine, but the physiological basis of its responses un-der water stress are largely unknown. For this purpose, an ecophysiological assessment of the conventional 110 -Rich-ter (110R) and SO4, and the new M1 and M4 rootstocks was carried out in ungrafted potted plants. During one season, these Vitis genotypes were grown under greenhouse con-ditions and subjected to two water regimes, well-watered (WW) and deficit irrigation (DI). Water potentials of plants under DI down to <-1.4 MPa, and net photosynthesis (AN) <5 mu mol CO2m-2s-1 did not cause leaf oxidative stress damage compared to WW conditions in all genotypes. The antioxidant capacity was sufficient to neutralize the mild oxidative stress suffered. Under both water regimes, gravimetric differences in daily water use were observed among genotypes, lead-ing to differences in the biomass of roots and shoots. Under WW conditions, SO4 and 110R were the most vigorous and M1 and M4 the least. However, under DI, SO4 exhibited the greatest reduction in biomass, while 110R showed the low-est. Remarkably, under these conditions, SO4 reached the least negative stem water potential and showed the highest hydraulic conductance values. Conversely, M1 reduced the most stomatal conductance, transpiration and AN. Overall, 110R achieved the highest biomass water use efficiency in re-sponse to DI, and SO4 the lowest, while M-rootstocks showed intermediate values. Our results suggest that there are dif-ferences in water use regulation among genotypes attributed not only to differences in stomatal regulation but also to plant hydraulic conductance. Therefore, it is hypothesized that dif-ferences in genotype performance may be due to root ana-tomical-morphological differences and to several physiologi-cal processes such as growth inhibition, osmotic adjustment, antioxidant production, nutrient translocation capacity, etc. Further studies are needed to confirm these differential eco-physiological responses of Vitis species under water stress, particularly under field and grafted conditions.