Characterizing Drought-Induced Responses in Grapevine (Vitis) Root Systems

Water scarcity threatens agricultural production in arid growing regions around the globe, and changing climatic conditions are expected to exacerbate this situation. To optimize production under these conditions, growers require plant materials that better tolerate drought stress to enable conservation techniques like deficit irrigation. To improve drought resistance of rootstocks for use in viticultural production, Vitis species originating from arid regions of the southwestern US hold tremendous potential. Several species originate from arid regions suggesting the existence of putative drought resistance traits that could improve grapevine rootstock performance under water limited conditions. In 2019 and 2020, grapevine genotypes Vitis aestivalis (accession T52), Vitis acerifolia (9018), Vitis arizonica (b40-14), Vitis riparia (TXNM0821), Vitis rupestris (Vru42), Vitis vulpina (V57-96) were grown from herbaceous cuttings and subjected to a controlled dry down (“drought”) or maintained well-watered. During the controlled dry down, bulk soil moisture (SM) was reduced gradually from 80% w/w to reach a target of 20–30% w/w over ~2 weeks. Treatments were then held for an additional 3-4 weeks. The intended control and drought conditions imposed during the potted vine dry down experiment were evaluated with soil moisture and physiological measurements. Most striking in my research is the discovery that among the six species that were studied, cortical lacuna occurred at lower levels of water stress and more frequently overall in V. rupestris; this could help explain variable drought resistance traits among commonly used rootstocks that originate from this and other species. Consistent with expectations, the drought treatment increased root suberization, which reduces fine root conductivity, but did so differentially among the species. V. riparia exhibited the highest suberin development under both drought and control conditions, which is consistent with patterns documented previously for rootstocks with this species parentage. V. rupestris had the highest number of root tips of all species, which corresponds to its lowest percent suberization measured from the colored images and indicates production of new growth and active water uptake sites. Characterization of root morphology via image analysis revealed differences in root function among species. Species that exhibited greater transport capacity were V. acerifolia > V. aestivalis > V. vulpina, while species with more absorptive capacity were V. arizonica > V. rupestris > V. riparia. Overall, this work demonstrated differential responses of diverse Vitis species to drought stress with respect to fine root anatomy, root architecture, and implied physiological function