Authors: Anna Buetow | Student in the WSU Research and Extension Experiences for Undergraduates Program, Summer 2023 | Home institution: Whitman College – Walla Walla, WA
Carol McFarland | Associate in Research with the PNW Farmers’ Network
Dr. Rachel Wieme | Extension Specialist, WSU Extension Walla Walla County
This article highlights the work of USDA-funded Research and Extension Experience for Undergraduates program which aims to expose students from WSU and other universities to different career paths in agriculture and provide them with skills for advancing their professional development.
Components of drought resilience include environmental conditions and how the plant responds to stress. Both an unfavorable climate and farming practices can increase stress on a plant, affecting its growth through signaling hormones. Patterns in plant hormone signaling pathways contribute specifically to the plant’s growth and maintenance in low water climates, and adaptive responses to stress.
Auxin is characterized as a central signaling hormone, as it impacts many processes in the plant, including growth, reproduction, and how the plant retains water. Auxin signals the plants to grow their shoots toward the light and also promotes root growth, reproduction, and water uptake. The only naturally occurring auxin in plants, called indole-3-acetic acid (IAA), has a fascinatingly widespread reach on several specific plant biochemical pathways with further downstream effects in multiple signaling cascades. The functional basis of this molecule is useful commercially in the development of pesticides specific to plant species, like broadleaf herbicides, as well as informing the understanding around communication pathways, ion transport mechanisms and protein sequences of plants. Plant stress reduction is vital in managing how crops would utilize their resources.
In low-water or high stress environments, auxin accumulates in damaged wheat cells to signal for repair. Different kinds of damage, including drought and physical damage, cause hormone pathways to respond in different ways, often termed signaling cascades. Such cascades have impacts on vascular plant circulation and gene transcription. Beneficial effects include the responsive transcription and translation of enzymes mediating and inhibiting reactive oxygen species (ROS). ROS play a role in the successful infection of Puccinia triticina on wheat, also known as wheat leaf rust. Hydroxyl radicals, super hydroxides, and hydrogen peroxide can down-regulate enzyme expression leading to successful infection. The presence of ROS in wheat is also linked to root decay. Inhibition of ROS prevents oxidative stress in the growing crop. In drought, ROS overproduction is induced which leads to the disruption of membrane integrity and osmotic balance in plant cells, resulting in reduction of overall crop yield and even plant death.
Wheat, as a vascular plant, has several different modes of transport for both intercellular signaling and nutrient transport. The two central hormone transport systems in vascular plants include polar and nonpolar transport. Polar transport of auxin works in a specific direction through parenchymatic cells, which are found towards the inner part of the straw and serve in water transport and storage in the plant since they are very thin and more permeable. This kind of transport is beneficial for how water is stored in the plant and is activated through root auxin accumulation. Nonpolar transport works through the phloem, which is the vascular pathway moving photosynthates and hormones to the root cells, who do not photosynthesize on their own. This kind of auxin transport is beneficial to root system growth and water uptake in the soil.
Reducing plant stress is the best way to take full advantage of auxin signaling. Auxin response factors in a stressed plant induce root growth arrest, decrease lateral root formation, and the rapid redirection of the root away from stress. This means nutrients and plant resources would be redirected to root system adaptation instead of aboveground biomass and therefore reduce yield. Farm management practices can be used mitigate drought-induced plant stress by increasing available soil moisture. Many studies show increases in soil organic matter leads to corresponding increases in soil moisture retention under reduced tillage practices in Eastern WA (Bista et al., 2017). These studies are supported by grower experiences reported in recent survey by WSDA, where 46.8% of respondents indicated increased yields and 71.5% reported increases in soil moisture after transitioning to reduced- or no-till systems (Gelardi et al., 2023).
Soil organic matter (SOM) is previously-living biological matter in various states of decomposition, such as plant residues and microbes. SOM has the potential to hold up to 20 times its weight in moisture (Reicosky, 2005) to benefit crop growth, and contributes to a healthy soil microbiome, which can reduce the need for some pesticides and fertilizers. Practices for increasing SOM on a large scale can include reduction of tillage or integrating cattle for manure and recycling plant residue. More methods include cover cropping with nitrogen fixers like legumes, to return nutrients to the soil. This would reduce fertilizer cost and contribute to a healthy soil pH and nutrient content.
Moisture management to reduce plant stress is central to optimizing dryland grain production in Eastern Washington. Many growers have been finding that incorporating no-till practices, adding organic matter, cover cropping, reducing synthetic inputs, increasing biodiversity, and livestock integration supports increased water holding capacity and overall soil health are strategies that support increased yield and drought resilience. More information is available on the CSANR Publication Resources, the WSU Wheat and Small Grains website, and to hear personal experiences of growers who are trying these practices, check out the PNW Farmers’ Network’s On-Farm Trials Podcast.
References:
Bista, P., S. Machado, R. Ghimire, G. Yorgey, and D. Wysocki. Chatper 3: Conservation Tillage Systems in Yorgey and Kruger (eds). 2017. Advances in Dryland Farming in the Inland Pacific Northwest. Washington State University Extension.
Gelardi, D, Roy, M., Hancock, J. 2023. Soil Management in Washington’s Dryland Wheat: WSDA Survey Results. Washington State Department of Agriculture. AGR Publication No. 103-166.
Reicosky, D.C. 2005. Alternatives to mitigate the greenhouse effect: emission control by carbon sequestration. In: Simpósio sobre Plantio direto e Meio ambiente; Seqüestro de carbono e qualidade da agua, pp. 20-28. Anais. Foz do Iguaçu, 18-20 de Maio 2005.
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