By Maicy Vossen, University of Minnesota
Knowing which traits relate to freezing tolerance in turfgrass is only part of the solution to improving winter hardiness. Being able to identify these traits quickly and efficiently is also another piece to the puzzle to select for more freeze tolerant plant materials. For example, many current practices utilize controlled growing environments to grow plants and subject them to acclimation and freezing regimes to determine which plants are freezing tolerant. This method can be accomplished more quickly but doesn’t always accurately represent results from field trials. Another method to evaluate winter hardiness is to grow plants in a field plot and evaluate survival after months in winter conditions. This method doesn’t require specialized growth chambers but takes much longer to yield results and each winter comes with unpredictable differences leading to confounding results between years. Both methods come with their positives and negatives, but overall, each requires significant time and space.
For my thesis project, I am developing methods of freeze tolerance evaluation in perennial ryegrass (Lolium perenne) through trait identification using non-destructive methods that do not require a freezing event. Previous blog posts have described the interconnected nature of freeze tolerance and the size of water-conducting metaxylem, which is a focus of this project (Vossen, 2023). Metaxylem size is an inherent trait in plants that can be measured without acclimation and freezing treatments. We have shown that freeze susceptible genotypes of perennial ryegrass have significantly larger leaf vascular bundles, metaxylem, and root metaxylem than freeze tolerant genotypes (Figure 1). To measure metaxylem size, we must destructively harvest the small turfgrass leaves and carefully cut thin slices of tissue to view under microscopy. This method is not without challenges, so we seek another way to estimate metaxylem size. Studies in other species have revealed connections between metaxylem size, transpiration, stomatal conductance, and water use efficiency in plants (Fichot et al., 2009; Tamang et al., 2021). Transpiration rate is a trait that we can identify through non-destructive methods in plants. If we can pinpoint the connectedness of metaxylem size and transpiration in perennial ryegrass, we can use transpiration rate as a method of estimating freeze tolerant genotypes.
References
Fichot, R., Laurans, F., Monclus, R., Moreau, A., Pilate, G., & Brignolas, F. (2009). Xylem anatomy correlates with gas exchange, water-use efficiency and growth performance under contrasting water regimes: Evidence from Populus deltoides x Populus nigra hybrids. Tree Physiology, 29(12), 1537–1549.
Laser Ablation Tomography. (2023). Roots lab: Research methodology.
Tamang, B., Lopez, J., McCoy, E., Haaning, A., Sallam, A., Steffenson, B., Muehlbauer, G., Smith, K., & Sadok, W. (2021). Association between xylem vasculature size and freezing survival in winter barley. Journal of Agronomy and Crop Science, 2022(208), 362–371.
Vossen, M. (2023). Taking a closer look at perennial ryegrass vascular tissue. University of Minnesota: WinterTurf.