Corn Brace Roots

• Roots of the corn plant that grow from nodes above the soil line are commonly referred to as brace roots.
• Brace roots are found on corn, as well as several other grasses such as sugarcane, sorghum, pearl millet, and foxtail millet.
• Despite being a familiar feature of corn plants, the functions of brace roots in supporting plant growth and productivity are not necessarily well understood.
• The name "brace roots" suggests obvious importance in anchoring and stabilizing the plant, but even this function has only recently been conclusively demonstrated by research.

• A corn plant produces two root systems – the seminal root system and the nodal root system.
• The seminal root system is comprised of the radicle and up to three pairs of lateral seminal roots. The seminal roots originate from within the seed embryo and sustain the corn seedling for the first couple of weeks after emergence.
• The nodal roots are the main root system that sustains the plant through the growing season. Nodal roots develop sequentially from individual nodes above the mesocotyl.
• Brace roots are a subset of the nodal roots that originate above the soil line.
• Roots from the first five stem nodes typically emerge below ground with the first four packed tightly together and the first noticeable internode between nodes four and five.
• The first set of brace roots emerges from node 6 (Figure 1), with additional sets of brace roots emerging from node 7 and higher in some cases.
• Brace roots do not always reach the soil, particularly those above node 6. These are referred to as aerial brace roots.

• Recent research has shown that brace roots that penetrate the soil do indeed play an important role in stabilizing the plant and reducing horizontal movement due to wind (Reneau et al., 2020).
• In addition to stabilizing the plant, brace roots also help anchor it, protecting against upward uprooting force exerted on the root system (Obayes et al., 2022).
• On plants with more than one node of brace roots that penetrate the soil, the roots from the lower node contribute the most to plant stability because they are anchored more deeply in the soil.

• New brace roots commonly emerge after a lodging event from the side of the stalk facing the soil (Figure 2).
• The exact mechanism that triggers this development is not known; gravitropism (plant response to gravity) could play a role (Sparks, 2023).
• Although it would seem apparent that this response is an adaptation to help the plant stabilize and recover following a lodging event, the extent to which these brace roots actually benefit the lodged plant remains unclear.

• The role of brace roots in water and nutrient uptake was undetermined until recently.
• Xylem elements – the vascular tissue of plants responsible for water and nutrient transport – are large and numerous in brace roots, suggesting they play an important role in water and nutrient uptake.
• Recent research has shown that brace roots that penetrate the soil do indeed take up water and nitrogen and the larger the roots, the greater the uptake (Rasmussen et al., 2022).

• It is commonly believed that brace roots in corn develop in response to stress on the plant.
• Brace root development is influenced by genetics and environment. Although brace root development can be influenced by stress conditions, their presence is not necessarily an indicator of stress on the plant (Sparks, 2023.)

• Corn plants routinely produce brace roots that never reach the soil, which raises the question as to why they do this and whether this is a waste of plant resources that could be more productively allocated to grain production.
• Brace roots are not a discrete system that the plant turns on or off as needed, they are linked to growth of the entire nodal root system and plant growth overall.
• As long as the plant is actively growing, new nodes of brace roots will be produced and brace roots that have penetrated the soil will continue to grow.
• A healthy plant with robust vegetative growth will also tend to set more brace roots.
• It’s common for plants along field edges to produce more nodes of brace roots (Figure 7). These plants may also have a second ear and tillers – they can add more growth because they have less competition for resources from other plants.
• In some cases, excessive brace root production may be indicative of some sort of problem that is causing sugars to accumulate in the lower portion of the plant, which the plant then diverts into producing roots.

Brace Roots Gone Wild

• An extreme example of both of these factors can be observed when a corn hybrid adapted for tropical environments is grown in the Corn Belt.
• When outside of their zone of adaptation, these plants will often fail to fill out an ear and will continue adding vegetative growth late into the season, growing extremely tall.
• As the plants continue to grow, they continue to initiate new nodes of brace roots. As many 12 nodes have been observed on tropical hybrid plants grown at the Corteva Agriscience research station in Johnston, IA (Figure 8).

• Obayes, S.K., L. Timber, M. Head, and E.E. Sparks. 2022. Evaluation of brace root parameters and its effect on the stiffness of maize, in silico plants. 4: diac008.
• Rasmussen A., L. Erndwein, A. Stager, J.W. Reneau, and E.E. Sparks. Preprint. Bigger is better: Thicker maize brace roots are advantageous for both strength and nitrogen uptake. bioRxiv, 2022. (doi.org/10.1101/2022.10.01.510439)
• Reneau, J.W., R.S. Khangura, A. Stager, L. Erndwein, T. Weldekidan, D.D. Cook, B.P. Dilkes, and E.E. Sparks. 2020. Maize brace roots provide stalk anchorage. Plant Direct 4: e00284.
• Sparks, E,E. 2023. Maize plants and the brace roots that support them. New Phytologist. 237: 48–52.
• Van Deynze, A., P. Zamora, P.-M. Delaux, C. Heitmann, D. Jayaraman S. Rajasekar, D. Graham, J. Maeda, D. Gibson, K.D. Schwartz et al. 2018. Nitrogen fixation in a landrace of maize is supported by a mucilage-associated diazotrophic microbiota. PLoS Biology 16: e2006352.