Impact of Severe Drought Stress on Water Relations of Young Cherry Trees Grafted onto Growth-Reducing Rootstocks

Vigor-reducing rootstocks are now commonly used in sweet cherry cultivation. However, their application in Hungary presents challenges due to the drier summer climate and limited availability of irrigation water. The aim of this study was to determine the water transport characteristics and potential drought tolerance of three vigor-reducing rootstocks that may be suitable for cherry production in Hungary. The stomatal conductance (gs), midday stem water potential (MSWP), and sap flow velocity were measured in four-year-old Carmen and Regina cherry trees grafted onto MaxMa 14, WeiGi 2, and GiSelA 6 rootstocks. Measurements were taken after harvest during a period of severe drought. Among the rootstocks studied, MaxMa 14 trees exhibited the lowest MSWP values, even after irrigation and during periods with a relatively adequate water supply. No significant or consistent differences in the gs values were observed between the rootstocks. However, the variation in the gs and MSWP values before and after irrigation was the greatest in MaxMa 14 trees and the smallest in GiSelA 6 trees. Furthermore, the sap flow velocity in MaxMa 14 trees showed no significant difference between the pre- and post-irrigation measurements, indicating stable water transport. In contrast, trees on GiSelA 6 and WeiGi 2 rootstocks exhibited significant differences between dry and irrigated conditions. Although MaxMa 14 showed lower MSWP values, its gs responded more dynamically to changes in the water availability, and it maintained consistent water transport parameters across both dry and wet conditions. Based on the evaluated parameters, GiSelA 6 and WeiGi 2 showed similar behavior. However, in regard to some traits—such as the dynamic change in stomatal conductance—WeiGi 2 appeared to be more similar to MaxMa 14. Our results suggest that MaxMa 14 may be the most adaptable to drought among the tested rootstocks.