Drought poses the greatest threat to global food production. Current agricultural practices use ≈70% of the available water; to meet the demands of a growing global population, water consumption will need to increase by 70% to 90% by 2050 (Molden, 2007; Somerville and Briscoe, 2001). This untenable demand for water is further exacerbated by the predicted increase in severity of erratic weather and drought due to climate change (Trenberth, 2011). As such, it is of utmost importance that agricultural production systems improve crop resilience and efficiencies in water resource utilization.
A plant’s ability to respond and adapt to drying soils directly impacts its ability to withstand brief dry periods and also avoid long-term drought stress. Plants have evolved intricate molecular, biochemical, and morphological responses to water stress (Bray, 1997; Hsaio, 1973; Shao et al., 2008). These responses can be grouped into either dehydration tolerance and/or dehydration avoidance based on their physiological impacts under drought conditions (Blum, 2005; Levitt, 1972). Dehydration tolerance refers to adaptations that allow a plant to maintain function even in a dehydrated state (Levitt, 1972). Examples of these are relatively rare and exotic and include such mechanisms as seed embryo dehydration and the dehydration tolerance seen in the resurrection plant (Craterostigma plantagineum). Developing more resilient food crops that use dehydration tolerance mechanisms is difficult due to the rarity of these traits among species (Blum, 2005). Dehydration avoidance is defined as the ability to maintain water status under limited water conditions (Levitt, 1972). These traits include early flowering, reduced leaf area, stomatal closure, increased root:shoot ratio, alteration of root morphology and architecture, and osmotic adjustments (Blum, 2005).
Full or partial stomatal closure is one of the earliest drought avoidance responses to water stress and limits transpirational water loss; however, this reduction in gS leads to a concomitant reduction in CO2 diffusion and consequent reduction in photosynthesis and carbon assimilation (Chaves, 1991; Hsaio, 1973). As such, developing more drought tolerant crops based on stomatal traits may improve overall water use, but it can lead to yield reductions even under well-watered conditions (Deikman et al., 2012).
As the site of water uptake and plant-soil interface, root systems have been the focus of substantial drought stress research. Numerous root system phenotypes based on depth, spatial distribution, and diameter have been shown to improve water acquisition under limiting conditions (Comas et al., 2013; Ho et al., 2005; Huang and Eissenstat, 2000; Mickelbart et al., 2015). Unfortunately, breeding for specific root system phenotypes while maintaining elite fruit traits is exceedingly difficult (Malamy, 2005; Wasson et al., 2012). One potential means to selecting both fruit and root traits is through grafting.
Essentially a root transplant, grafting offers the ability to manage numerous soil-borne pathogens that affect solanaceous and cucurbitaceous crops (Louws et al., 2010). Furthermore, recent work has demonstrated the ability of rootstocks to improve fruit quality, soil resource use efficiency, as well as combined biotic and abiotic stress tolerance (Kyriacou et al., 2017; Rouphael et al., 2018). Certain rootstocks have demonstrated the ability to improve water use efficiency in susceptible scions (Djidonou et al., 2013; Schwarz et al., 2010). In their open-field grafted tomato study, Djidonou et al. (2013) showed that rootstocks can increase irrigation water use efficiency regardless of water regime applied. This response indicates a constitutive rootstock effect on growth and yield. Many of the commercially available rootstocks, including those shown to improve water use efficiency, have significantly different root system morphologies (Suchoff et al., 2017). Whether these rootstocks respond differently to drying soils at a root system morphological level is unknown. As such, the objectives of the following study were to 1) compare root systems of two commercially available tomato rootstocks with different root system morphology when reducing available water; 2) determine if root system morphology in tomato rootstocks changes with available water; and 3) compare rootstock effects on scion morphology and physiology with reduced available water.
Al-Harbi, A., Hejazi, A. & Al-Omran, A. 2017 Responses of grafted tomato (Solanum lycopersicon L.) to abiotic stresses in Saudi Arabia Saudi J. Biol. Sci. 24 1274 1280
Blum, A. 2005 Drought resistance, water-use efficiency, and yield potential – are they compatible, dissonant, or mutually exclusive? Austral. J. Agr. Res. 56 1159 1168
Bouma, T.J., Nielsen, K.L. & Koutstaal, B.A.S. 2000 Sample preparation and scanning protocol for computerized analysis of root length and diameter Plant Soil 218 185 196
Comas, L.H., Becker, S.R., Von Mark, V.C., Byrne, P.F. & Dierig, D.A. 2013 Root traits contributing to plant productivity under drought Front. Plant Sci. 4 442
Deikman, J., Petracek, M. & Heard, J.E. 2012 Drought tolerance through biotechnology: Improving translation from the laboratory to farmers’ fields Curr. Opin. Biotechnol. 23 243 250
Djidonou, D., Zhao, X., Simonne, E.H., Koch, K.E. & Erickson, J.E. 2013 Yield, water-, and nitrogen-use efficiency in field-grown, grafted tomatoes HortScience 48 485 492
Henry, A., Cal, A.J., Batoto, T.C., Torres, R.O. & Serraj, R. 2012 Root attributes affecting water uptake of rice (Oryza sativa) under drought J. Expt. Bot. 63 4751 4763
Hernández, E.I., Vilagrosa, A., Pausas, J.G. & Bellot, J. 2010 Morphological traits and water use strategies in seedlings of Mediterranean coexisting species Plant Ecol. 207 233 244
Ho, M.D., Rosas, J.C., Brown, K.M. & Lynch, J.P. 2005 Root architectural tradeoffs for water and phosphorus acquisition Funct. Plant Biol. 32 737 748
Huang, B. & Eissenstat, D.M. 2000 Linking hydraulic conductivity to anatomy in plants that vary in specific root length J. Amer. Soc. Hort. Sci. 125 260 264
Ibrahim, A., Wahb-Allah, M., Abdel-Razzak, H. & Alsadon, A. 2014 Growth, yield, quality and water use efficiency of grafted tomato plants grown in greenhouse under different irrigation levels Life Sci. J. 11 118 126
Kumar, P., Rouphael, Y., Cardarelli, M. & Colla, G. 2017 Vegetable grafting as a tool to improve drought resistance and water use efficiency Front. Plant Sci. 30 1130
Kyriacou, M.C., Rouphael, Y., Colla, G., Zrenner, R. & Schwarz, D. 2017 Vegetable grafting: The implications of a growing agronomic imperative for vegetable fruit quality and nutritive value Front. Plant Sci. 8 741
Lawlor, D.W. & Cornic, G. 2002 Photosynthetic carbon assimilation and associated metabolism in relation to water deficits in higher plants Plant Cell Environ. 25 275 294
Levitt, J. 1972 Responses of plants to environmental stresses. Vol. 2: Water, radiation, salt and other stresses. Academic Press, New York
Louws, F.J., Rivard, C.L. & Kubota, C. 2010 Grafting fruiting vegetables to manage soilborne pathogens, foliar pathogens, arthropods and weeds Scientia Hort. 127 127 146
Manavalan, L.P., Guttikonda, S.K., Nguyen, V.T., Shannon, J.G. & Nguyen, H.T. 2010 Evaluation of diverse soybean germplasm for root growth and architecture Plant Soil 330 503 514
Mickelbart, M.V., Hasegawa, P.M. & Bailey-Serres, J. 2015 Genetic mechanisms of abiotic stress tolerance that translate to crop yield stability Nat. Rev. Genet. 16 237 251
Molden, D. (ed.). 2007 Water for food, water for life: A comprehensive assessment of water management in agriculture. International Water Management Institute. Earthscan, London, UK
Nilsen, E.T., Freeman, J., Grene, R. & Tokuhisa, J. 2014 A rootstock provides water conservation for a grafted commercial tomato (Solanum lycopersicum L.) line in response to mild-drought conditions: A focus on vegetative growth and photosynthetic parameters PLOS One 9 e115380
President’s Council of Advisors on Science and Technology (PCAST) 2012 Report to the president on agricultural preparedness and the agriculture research enterprise. Executive Office of the President, President’s Council of Advisors on Science and Technology, Washington DC
Rivard, C.L. & Louws, F.J. 2006 Grafting for disease resistance in heirloom tomatoes. North Carolina Coop. Ext. Serv. Bul. Ag-675. NC State Univ., Raleigh, NC
Rouphael, Y., Kyriacou, M.C. & Colla, G. 2018 Vegetable grafting: A toolbox for securing yield stability under multiple stress conditions Front. Plant Sci. 8 2255
Schwarz, D., Rouphael, Y., Colla, G. & Venema, J.H. 2010 Grafting as a tool to improve tolerance of vegetables to abiotic stresses: Thermal stress, water stress and organic pollutants Scientia Hort. 127 162 171
Shao, H.-B., Chu, L.-Y., Jaleel, C.A. & Zhao, C.-X. 2008 Water-deficit stress-induced anatomical changers in higher plants C. R. Biol. 331 215 225
Suchoff, D.H., Schultheis, J.R., Kleinhenz, M.D., Louws, F.J. & Gunter, C.C. 2018 Rootstock improves high-tunnel tomato water-use efficiency HortTechnology 28 344 353
The United Nations 2000 Secretary-general, in address to developing countries “south summit”, calls for steps to make global economy more equitable [Press release]. 21 Mar. 2018. <https://www.un.org/press/en/2000/20000412.sgsm7358.doc.html>.
United States Department of Agriculture Economic Research Service 2010 U.S. Tomato Statistics; State census farms with tomatoes, area harvested, & area irrigated, 1978-2007. 21 Mar. 2018. <http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1210>.
Wasson, A.P., Richards, R.A., Chatrath, R., Misra, S.C., Prasad, S.V. & Rebetzke, G.J. 2012 Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops J. Expt. Bot. 63 3485 3498