Lakyn Sonday - Masters Candidate

Years of selective breeding for malting standards have unintentionally connected flavor and quality traits to specific genes, creating some trade-offs.

Objective:

Identification of beneficial alleles controlling the length of five early growth traits.

 

Introduction:

Coleoptile, internode, phytomer, rhizomatous stem, and early root lengths are five important early growth traits that impact various aspects of plant development and early vigor. Overall success of a plant is often dependent on environmental factors and the adaptation of a barley variety. Drought tolerance, cold hardiness, pathogen infection rates, and uniform establishment have shown a connection to the traits measured during this research.

Early Growth Traits:

Phytomer

  • The combined structures that determine the total length of the emerging shoot from soil are measured from the seed to the emergence of the first leaf. The trait that influences the emergence and includes all early growth trait structures.  
  • Genetic potential in lengthening of the phytomer is important to delve into in order to control the length of the trait. Research suggests that phytomer length is controlled by multiple genes with additive effects. In wheat, the heritability of this trait was measured at 0.74 (Gul, 1978). 
  • Winter hardiness connection from the node located within this structure. Aids in deeper reach for access to resources during development.  
  • Genetic and environmental changes both impact the length of phytomer. Very low temperatures showed significant differences in lengthening ability, and a correlation between warmer temperatures and longer phytomers was seen (Kale, et al. 1973).   
  • The elongation of the plant cells within the phytomer is fundamentally driven by the plant hormone auxin, which enables said cell elongation. (Luo, et al. 2020).

            Internode

  • This is defined as the length from the seed to the first node that forms during stem development, below soil levels. The length of this measurement dictates the location of the first node, which is often crucial for development.
  • Having shorter first internodes proved that the node was deeper in the soil, aiding in cold tolerance of a variety (Gul et al. 1978; Poulous et al. 1987; Price et al. 2024).
  • A study of winter barley showed high genetic control of the length to the first node, 0.74 (Gul et al. 1978).
  • A nuanced connection in wheat has been made between the location of the first node, the length of the crown, and a plant's susceptibility to Fusarium crown rot. It was found that lines with shorter crowns often had less susceptibility, thought to be linked to the time of exposure of crown and developing leaf sheath to Fusarium at top soil levels (Wildermuth et al. 2001)

            Coleoptile

  • This is defined as the leaf sheath covering leaf tissue as it emerges from the soil.
  • Genetic variation has been seen in crops like wheat and barley that can provide opportunities to increase these traits, as well as early seedling vigor and potential drought tolerance (Luo et al., 2020). 
  • Researchers identified a QTL on barley chromosome 5H that are associated with longer coleoptiles. The allele linked to this QTL increased coleoptile length by ~21%, resulting in improved emergence and establishment under deep sown conditions and did not create unwanted changes to other agronomic traits (Gao et al., 2024).

            Rhizomatous Stem

  • This structure is defined as the length from the coleoptile to the first node. The location where secondary, or adventitious roots are formed (Dahleen, et al. 2007).
  • The length of the stem, which forms adventitious roots, comes primarily from the depth of planting and light availability to the plant, ensuring that stems can grow long enough to aid in reaching the soil surface (Allan, R. E., & Pritchett, J. A. 1973., E. Kirby, 1993).
  • Research has determined that this trait is controlled not by a single gene, but multiple genes with smaller effects, observed primarily from evidence of continued segregating generations. Dominance effects were observed for longer rhizomatous stems  (Gul, A. et al., 1978., Price, J. et al. 2024).
  • In drought conditions, having more adventitious roots and having them develop deeper in the soil provides more access to water (Grando, et al. 1994., Su. et al., 2021., Williams, et al. 2024.)  Adventitious root growth has also been linked to grain yield in two cultivars of two-row barley (Hockett, 1985).    

Primary Root Growth

  • -Modern cultivars now tend to have shorter and thicker seminal roots due to evolution and crop cultivation, where irrigation and nutrients are concentrated on the surface soil (Grando et al., 1995).
  • Shorter roots restrict seedlings' ability to reach deeper soil levels to collect moisture during periods of drought and can lead to lower structural stability (Grando et al., 1995). Negative impacts on the plant's growth and yield output in situations of drought.
  • The number of seminal roots is heritable, and genetic diversity in both wheat and barley was observed during greenhouse and field studies (Atta et al., 2013; Liu et al., 2020).
  • Deeper sowing levels reduce root mass during emergence (Kirby, 1993). The connection between deeper sowing and increased primary roots is crucial.

Summary:

  • Controlling and lengthening these traits could allow for deeper planting, enabling better establishment and greater access to water and nutrients
  • In this study there was no correlation to height, but we did see a link between lodging and lengthening of early growth traits. Is this because of planting depth or perhaps lengthening the stem leads to a weaker stem? If we lengthen these traits and don’t plant deeper, though, lodging could be severe.
  • Changing planting depth also risks the chance of having the primary node close to the surface, facing the cold.
  • Exploring the connection to adventitious roots. Does having a longer rhizomatous stem create more AR and does having more AR aid in plant development?
  • Continued research on the connection between early growth traits and Fusarium infection.
  • To protect from a cold frost in spring, creating crosses into winter barley material, lengthening these traits could add value.

Materials and Methods

  • 630 two-row barley lines from the USDA World Core Barley line were tested in greenhouse and field conditions. Heirloom accessions from all around the world have immense diversity and minimal breeding intervention.
  • The population was grown in the greenhouse in a complete block design for 3 reps on germination paper in buckets of water, deemed “root roll-ups”, with five seeds on each germination paper.
  • The five early growth traits were measured on the barley plants after the three-leaf stage, around 2-3 weeks from planting.
  • The lines were planted in the Bozeman field at the POST farm in an unreplicated setting to collect visual notes, emergence, height, lodging, and yield data on the lines.
  • Genome-wide Association Study to identify genetic variation for useful SNPs.