Study on the drought resistance of the grape variety Storgozia grafted onto different rootstocks

The study, conducted between 2017 and 2022, in the experimental vineyards of the Institute of Viticulture and Enology, Pleven, identified significant climatic changes in the region. The annual accumulated temperature consistently exceeded 4400°C, peaking at 4827.1°C in 2019. The period from 2019 to 2022 was the warmest of the decade, characterized by prolonged heatwaves and summer droughts. Precipitation during the growing season exhibited a persistent declining trend, reaching its lowest recorded value in the past 15 years (266.6 mm in 2022). A pattern of uneven rainfall distribution was observed, with a maximum between April and June and a minimum between August and October. An analysis of the response of the Storgozia grape variety, grafted onto four different rootstocks, revealed high to very high-water stress, varying in intensity across years and experimental variants. Concurrently across all experimental years, the control combination Storgozia/SO 4 exhibited the greatest vulnerability to drought, whereas the Storgozia/110 R combination consistently exhibited significantly greater drought tolerance. During the hot growing seasons of 2017, 2020 and 2022, various visual symptoms of water deficit were observed, and these symptoms were most pronounced in the Storgozia/SO 4 control variant and less severe in the Storgozia/Fercal variant. Statistical analysis confirmed the significantly higher drought resistance of vines grafted onto the 110 R rootstock, with statistically significant differences compared to the other rootstocks. The study highlights the increasing water stress in the Pleven region and emphasizes the suitability of the 110 R rootstock for the Storgozia grape variety in mitigating the adverse effects of drought.