1. Crop responses to rising evaporative demand: new opportunities for improving yields under drought
Increases in vapor pressure deficit (VPD) or 'atmospheric drought' are driving yield decreases in several key production environments across the globe. One way to mitigate such penalties is to design crop cultivars that either conserve water as VPD increases (drought-prone environments) or overcome unnecessary restrictions to crop water use under high VPD (well-watered environments). However, the genetic basis of such traits and where to precisely deploy them (geographically) remain unknown, resulting in a major bottlenecks to improving yields under this stress. In this research, we address this challenge by combining eco-physiological dissection, physiological phenotyping of mapping populations and crop simulation modeling.
Representative publications:
Novick, K., D. Ficklin, C. Grossiord, A. Konings, J. Martínez-Vilalta, W. Sadok, A.T. Trugman, A.P. Williams, A.J. Wright, J.T. Abatzoglou, M.P. Dannenberg, P. Gentine, K. Guan, M.R. Johnston, L.E.L. Lowman, D.J.P. Moore, and N. McDowell. 2024. The impacts of rising vapor pressure deficit in natural and managed ecosystems. Plant, Cell and Environment 47 (9), 3561-3589.
Monnens, D.M.‡, F. Ford Denison and W. Sadok. 2023. Vapor-pressure deficit increases nitrogen fixation in a legume crop. New Phytologist, 239(1): 54-65.
Tamang, B.G., D.M. Monnens, J.R. López, J.A. Anderson, B.J. Steffenson and W. Sadok. 2022. The genetic basis of transpiration sensitivity to vapor pressure deficit in wheat. Physiologia Plantarum, 174 (5), e13752.
López, J.R, D.A. Way and W. Sadok. 2021. Systemic effects of rising atmospheric vapor pressure deficit on plant physiology and productivity. Global Change Biology, 27 (9), 1704–1720.
Sadok, W., R. Schoppach, M.E. Ghanem, C. Zucca, and T.R. Sinclair. 2019. Wheat drought-tolerance to enhance food security in Tunisia, birthplace of the Arab Spring. European Journal of Agronomy, 107: 1–9.
2. Nocturnal transpiration in crops: magnitude, genetic variability and impact on yields
Nighttime temperatures are rising at a rate that is 1.4 times that of daytime temperatures. Such warming trends are causing increases in respiratory carbon losses and nighttime evaporative demand, which drives 'wasteful' nighttime transpiration. Because no photosynthesis occurs during the night, high nocturnal transpiration could be aggravate the severity of drought events. The goal of this research is to quantify the extent of nighttime transpiration in crops, its mechanistic basis and its relationship to yield under various water availability regimes.
Representative publications:
Schoppach, R., T.R. Sinclair, and W. Sadok. 2020. Sleep tight and wake-up early: nocturnal transpiration traits to increase wheat drought tolerance in a Mediterranean environment. Functional Plant Biology 47(12) 1117–1127.
Sadok, W. and S.V.K. Jagadish. 2020. The hidden costs of nighttime warming on yields. Trends in Plant Science, 25 (7), 644–651.
Schoppach, R, T.R. Sinclair and W. Sadok. 2020. Sleep tight and wake-up early: nocturnal transpiration traits to increase wheat drought tolerance in a Mediterranean environment. Functional Plant Biology, 47 (12): 1117–1127.
Sadok, W, J.R. López, Y. Zhang, B.G. Tamang, and G. Muehlbauer. 2020. Sheathing the blade: significant contribution of sheaths to daytime and nighttime gas exchange in a grass crop. Plant, Cell and Environment, 43 (8): 1844–1861.
3. The physiological bases of freezing tolerance in winter crops grown in northern climates
Deploying continuous living cover (CLC) crops that reliably overwinter is essential to farmer’s adoption of new cropping systems that protect Minnesota’s natural resources while creating new commercialization opportunities. However, a bottleneck facing several breeding programs of CLC crops is the slow progress in breeding for freezing tolerance. So far, phenotypic selection via survival rates is the only viable approach to breeding. The goals of this project are to identify ecophysiological traits that are associated with freezing survival and to use such traits to develop a phenotyping pipeline to support barley and winter pea breeding programs for enhanced winterhardiness. Photo Credit: Brian Steffenson.
Representative publications:
Price, J.H., W. Sadok, and K. P. Smith. 2024. Identifying indirect selection traits to improve winter hardiness in barley. Euphytica, 220, 117.
Sadok, W., JJ Wiersma, BJ Steffenson, SS Snapp and KP Smith. 2022. Improving winter barley adaptation to freezing and heat stresses in the US Midwest: bottlenecks and opportunities. Field Crops Research, 286, 108635.
Tamang, B.G., J.R. López, E. McCoy, A. Haaning, A. Sallam, B.J. Steffenson, G. J. Muehlbauer, K.P. Smith and W. Sadok. 2022. Association between xylem vasculature size and freezing survival in winter barley. Journal of Agronomy and Crop Science, 208 (3), 362–372.
Wiering, N.P., C. Flavin, C.C. Sheaffer, G.C. Heineck, W. Sadok, and N.J. Ehlke. 2018. Winter hardiness and freezing tolerance in a hairy vetch collection. Crop Science, 58 (4): 1594–1604.
4. The physiological and genetic bases of heat stress tolerance in temperate crops
Minnesota-grown crops are subject to high temperature stress in the summer. Evidence shows that historical increases in temperature during the summer drove yield decreases of locally grown crops such as oat and barley, which prompted growers to look for more profitable and resilient crops such as corn and soybean. This project aims at identifying heat stress tolerance traits and genetic markers that will be leveraged in an ongoing breeding program to release more resilient varieties towards heat stress events that are expected to increase in frequency and intensity in Minnesota. Photo Credit: José López.
Representative publications:
López, J.R., B.G. Tamang, D.M. Monnens, K.P. Smith and W. Sadok. 2022. Canopy cooling traits associated with yield performance in heat-stressed oat. European Journal of Agronomy, 139, 126555.
Sadok, W., J.R. López and K.P. Smith. 2021. Transpiration increases under high‐temperature stress: Potential mechanisms, trade‐offs and prospects for crop resilience in a warming world. Plant, Cell and Environment, 44 (7), 2102–2116.
5. Unraveling the physiological bases of yield increase in annual and perennial grass crops
Improving cereal yields requires a mechanistic understanding of physiological limits to yield increases. Surprisingly however, we know relatively little about these limits. At the same time, current domestication efforts, particularly those targeting breeding for higher-yielding perennial crops need to be informed by such knowledge. This research aims at 1) mapping the physiological drivers of historical yield increases in wheat and barley, 2) discovering new traits related to resource use efficiency, and 3) leverage these findings to better understand the physiological basis of interannual yield decline in intermediate wheatgrass, a promising perennial grain crop. For all crops, the goal is to derive from this research breeding targets to increase their yield potential.
Ding, Q., X. Zhen, J. M. Jungers and W. Sadok. 2025. Association between leaf senescence dynamics and age-related yield decline in the perennial grain crop intermediate wheatgrass. Annals of Botany (in press).
Zhen, X., Y. Zhang, J.R López, G. Muehlbauer, and W. Sadok. 2025. Leaf sheath stomata density is a driver of water use in grasses: genetic and physiological evidence on barley. Journal of Experimental Botany 76 (17), 5025-5036.
Ding, Q., X. Zhen, and W. Sadok. 2025. Photosynthesis-driven yield gains in global wheat breeding trials. Crop Science 65 (1), e70005.
Zhen, X., M. Dobbratz, J. M. Jungers and W. Sadok. 2024. Is interannual grain yield decline of intermediate wheatgrass influenced by management and climate in the Upper Midwest? Agriculture, Ecosystems & Environment, 362, 108856.
Funding sources: USDA-SCRI, Minnesota Wheat Research & Promotion Council, Minnesota Soybean Research & Promotion Council, Minnesota Department of Agriculture, Forever Green Initiative, University of Minnesota, NSF/CRDF, USDA-NIFA