Physiological responses to drought in four grapevine cultivars grown in the La Mancha wine region

Abstract

In the La Mancha wine region, grapevines are regularly exposed to drought and heat waves, while the necessary water resources to mitigate these effects are becoming increasingly scarce. Consequently, the physiology of cultivars is being affected, resulting in serious consequences for yield and quality. Understanding how cultivars behave in this area is key to selecting plant material for future vineyards. The present study aimed to assess the physiological behavior of the four cultivars experiencing the most significant growth in recent years in the La Mancha Designation of Origin (D.O.) when grown under rainfed conditions.

The study was conducted in the summer of 2025 in a multivarietal experimental vineyard located in Tomelloso, Spain (latitude: 39.17N, longitude: −3.00W). Over the study period, daily maximum temperatures and vapor pressure deficit (VPD) ranged from 23.8 to 39.4 °C and from 1.0 to 3.6 kPa, respectively. The cultivars studied were Bobal, Garnacha Tintorera, Monastrell, and Verdejo. All vines were grafted onto the same rootstock (110 Richter) and planted in 2002. During the experimental period, plants were not watered.

We conducted measurements of several physiological parameters during the hottest period of the growing season (June–August). Leaf osmotic potential at full turgor (π_o) was recorded three times, once per month, following the osmometer method (Bartlett et al., 2012). Gas exchange and leaf water potential (Ψ_L) were measured five times over the experimental period, always after midday, using the same leaf. Xylem hydraulic conductivity (K_h) and xylem pressure (Ψ_x) were measured using a flow meter and a pressure chamber, respectively. As in the previous case, these measurements were performed five times throughout the experimental period.

Results revealed that in general cultivars reduced π_o over time, as reported by Sinclair et al. (2024), although significant differences across cultivars were only observed in August. Osmotic adjustment was more pronounced in Bobal and Verdejo. In these cultivars, π_o decreased steadily, whereas in Garnacha Tintorera and Monastrell, it increased slightly between the last two measurements. Net assimilation (A_n), stomatal conductance (g_s), and midday water potential (Ψ_L) exhibited significant differences across cultivars. Bobal exhibited the highest A_n and g_s values. Differences in vulnerability to xylem embolism across cultivars were observed (Lamarque et al., 2023). A positive linear was observed between percentage loss of hydraulic conductivity (PLC) and Ψ_x values.

References

Bartlett, M. K., Scoffoni, C., Ardy, R., Zhang, Y., Sun, S., Cao, K., Sack, L. (2012). Rapid determination of comparative drought tolerance traits: using an osmometer to predict turgor loss point. Methods in Ecology and Evolution, 3(5), 880–888. https://doi.org/10.1111/j.2041-210X.2012.00230.x

Lamarque, L. J., Delmas, C. E., Charrier, G., Burlett, R., Dell’Acqua, N., Pouzoulet, J., Gambetta, G. A., & Delzon, S. (2023). Quantifying the grapevine xylem embolism resistance spectrum to identify varieties and regions at risk in a future dry climate. Scientific Reports, 13(1), 7724. https://doi.org/10.1038/s41598-023-34224-6

Sinclair, G., Galarneau, E. R., Hnizdor, J. F., McElrone, A. J., Walker, M. A. & Bartlett, M. K. (2024). Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis in hot conditions despite less drought-resistant leaves. Annals of Botany, 134(2), 205-218. https://doi.org/10.1093/aob/mcae032