Differential impact of commercial rootstocks on the physiological response of a common walnut scion to drought stress

Authors: MOMAYYEZI, MINA - University Of California, Davis; KNIPFER, THORSTEN - University Of British Columbia; HERNANDEZ PEREZ, ISABEL - University Of Antioquia; Kluepfel, Daniel; ALBUQUERQUE, CAETANO - University Of California, Davis; BAMBACH, NICOLAS - University Of California, Davis; DEGROM, JACK - University Of California, Davis; McElrone, Andrew

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Grafting is an ancient technique that involves the physical joining of genotypically distinct shoot and root systems, in order to achieve a commercially viable plant. Grafting is used in modern agriculture to improve biotic and abiotic stress tolerance, modify plant architecture, flowering and boost yields. However, despite the importance of the rootstock-scion combination in the walnut industry, there is an important lack of information on the communication and resulting modification that rootstock genotypes impart important metabolic responses in the scion such as drought tolerance. Previously we demonstrated a significant difference among the commercially available walnut rootstock genotypes and their response to drought stress. Here we report on our work to examine the ability of these genetically unique rootstocks to impart their response to drought conditions to the common scion genotype which was grafted across all rootstock genotypes. Interestingly, the rootstock genotype which exhibited the greatest degree of drought tolerance when grown on its own roots, imparted the greatest degree of drought tolerance to the grafted scion. These results suggest that graft compatible drought tolerant rootstock genotypes could be used to enhance canopy responses and limit yield losses under water limited conditions in commercial walnut orchards. In addition. this work supports the hypothesis that scion metabolism is strongly influenced by rootstock genotype which may open up many new options for growers to enhance the ability of grafted tree crops to cope with numerous stress combinations.

Technical Abstract: Rootstocks are commonly used in California walnut orchards to provide resistance to soil borne pests and other diseases. Little information exists about how these commercial rootstocks respond to water stress, which is becoming increasingly important in this semi-arid growing region where increased frequency and severity of droughts requires efficient use of available water resources. We previously found that three own-rooted walnut rootstocks (RX1, VX211 and Vlach) performed differently under droughts stress. Here, we evaluated whether similar responses were conferred to a common English walnut scion using a mini-lysimeter experimental platform in controlled growing conditions. Similar to our previous own-rooted study, RX1 conferred a higher growth rate to the common scion canopy that was associated with higher transpiration (E) and daytime canopy conductance under well-watered conditions. These enhancements lasted into the early stages of mild drought stress. All three rootstocks exhibited some level of nighttime E, but Vlach exhibited a higher proportion of total daily E occurring at night. The rootstocks all responded significantly to water stress with a decrease in canopy growth rate, gas exchange, and water potentials with decreasing soil moisture, but RX1 exhibited the highest leaf turgor under drought that was associated with lower osmotic potentials. RX1 also exhibited an intermediate increase in root biomass under drought, likely impacting carbon available for the canopy. Our results suggest that rootstocks and future genotypes could be used to induce differential canopy responses under water limited conditions in commercial walnut orchards.