Root-Pulling Force: Uncovering the Genetic Signal for Stronger Maize Roots

Source: 

Woods, P., Lehner, K. R., Hein, K., Mullen, J. L., & McKay, J. K. (2022). Root Pulling Force Across Drought in Maize Reveals Genotype by Environment Interactions and Candidate Genes. Frontiers in Plant Science, 13, 883209.https://doi.org/10.3389/fpls.2022.883209

Maize (Zea mays L.) is one of the world's most important food crops, and securing a stable yield of maize crops through increasing environmental challenges, such as prolonged drought seasons under the global warming trend, is critical for our future. Roots of maize help the plant anchor in the soil to capture nutrients, water and carbon that are needed to sustain the plant's wellness. Hence, understanding the genetic factors associated with strengths of the roots are important to ensure good growth of the plant, yet measuring the root traits especially at scale has been challenging since roots grow underground.

In a recent study, researchers used root-pulling force (RPF)-the vertical force required to extract a maize plant from the ground-as a simple, scalable technique to quantify root system strength in the field. With the RPF technique, the group has been able to conduct large-scale field experiments, measuring root systems of plants in thousands of plots under both full and limited irritations of watering (enough watering v.s. drought), allowing the team to examine how genetic variants associate with the environment to shape root traits.

Figure 1. Genome-wide association mapping of RPF under full-irrigated conditions. A significant genetic marker associated with variation in RPF is found on Chr10 near AMT5

Using genome-wide association studies (GWAS), the researchers identified a strong genetic signal on chromosome 10, indicating a genetic marker that is significantly (p-value < 1e-11) linked to variation in root pulling force, near gene AMT5 (Figure 1). The gene AMT 5 is involved actively in nitrogen transport that primarily expressed in maize roots. Plants carrying different genotypes at this marker showed consistently different root pulling force, with one genotype producing stronger roots than the other and the trend is consistent under both watering conditions (Figure 2). The genetic differences were also reflected in root system architecture: plants with the higher-RPF genotype developed larger root areas (Figure 2), and photographs of the extracted roots demonstrated visible denser and more extensive roots (Figure 3).

Figure 2. Measurements of Root Pulling Force (Left) and Root Area (Right), comparing different genotypes at the AMT5 marker (Com. v.s. Alt. allele) and under two watering treatments (Full v.s. limited). Trends in root area and root-pulling force are closely aligned, indicating that RPF is a reliable measure of maize root size and overall root system strength.

Figure 3. Representative root photos for lines with the common allele genotype (Top) or alternate allele genotype (Bottom).

By identifying genetic markers strongly associated with variation in root strength, field scientists and plant breeders can promote the expression of high-RPF alleles through selective breeding or targeted genetic editing, thereby improving maize root growth. Stronger roots protect early plant development, leading to more consistent crop emergence and more stable yields. These improvements support farmers throughout crop establishment, harvesting, and overall farm operations. More importantly, the study demonstrates that root-pulling force (RPF) is a simple yet reliable measurement that can be applied at scale, making it a practical tool for large field-based genetic studies.