Apple rootstock response to threshold water management during six weeks of progressing drought

Authors: Bierer, Andrew; Tang, Lisa; Viands, Kamryn; WOLCOTT, CAROLINE - Virginia Tech

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2025
Publication Date: 1/8/2026
Citation: Bierer, A.M., Tang, L., Viands, K.E., Wolcott, C. 2026. Apple rootstock response to threshold water management during six weeks of progressing drought. Journal of the American Society for Horticultural Science. 151(1):38-49. https://doi.org/10.21273/JASHS05526-25.
DOI: https://doi.org/10.21273/JASHS05526-25

Interpretive Summary: An automated device controlled plant available water content during a progressing drought trial of young apple trees. Physiologic parameters usually associated with water stress were measured as the autonomous device decreased plant available water by 5% each week. Apple rootstock varieties (B.10, B.9, G.11, G.935, G.969) grafted to a common honeycrisp scion were selected to allow inference on rootstock conveyance of plant response to water stress encountered during the trial; dwarfing nature and the two breeding lines were also of interest. Destructive sampling indicated the B.10 variety amassed additional below ground biomass in proportion to other varieties under study. The B.10 variety responded to water deficit with an inclination to maintain C assimilation, while the G.935 variety was significantly more sensitive to the onset of water stress and exhibited a high relative ability for stomatal control. A marginal difference in C assimilation rate by cultivar was suggested. It is clear that rootstock variety has a meaningful impact on scion response to water stress and that different survival strategies can be selected for by choice of rootstock.

Technical Abstract: Containerized second-leaf apple, Malus domestica, nursery rootstock (B.10, B.9, G.11, G.935, G.969) grafted to common Honeycrisp scion were subjected to six weeks of progressive drought and physiology assessment. An autonomous control system, “Open_Irr”, was programmed to decrease plant available water content in a mineral soil matrix by 5% each week. Observed growth and aspects of photosynthetic function were assessed by infrared gas analyzer, porometer, and Scholander pressure chamber during the progressing drought to facilitate observation of rootstock varietal conveyance of response to drought conditions, while orthogonally contrasting breeding series (Geneva, Budagovsky) and dwarfing nature (dwarfing, semi-dwarfing). The G.935 rootstock was sensitive to drought onset with absolute (2 mmol H2O m-2s-1) and relative (42%) declines in transpiration over two weeks while remaining cultivars maintained or increased transpiration rates (+0.5 mmol H2O m-2s-1, pooled) over the same period. Orthogonal contrast estimates of C assimilation by breeding series in week two and six, respectively 2.2 and 1.8 umol CO2 m-2s-1, suggests a marginal photosynthetic rate advantage of the Budagovsky series during water limitation. Biomass proportions were measured upon excavation and indicated the B.10 rootstock allocated additional resources to belowground biomass (0.67 v. 0.52, pooled) before and/or during drought imposition. Scholander chamber measures supported the observed sensitivity of the G.935 variety to drought onset as turgor pressures of 27 bar were encountered during the first week of drought imposition. Rootstock variety conveys aspects of abiotic stress response of the scion, implying a meaningful choice in selection of pairings where regional droughts are of concern or where access to irrigation infrastructure is limited. Additionally, there is an underlying mechanism for stomatal regulation proclivity exhibited by the G.935 rootstock warranting additional evaluation.