By Xin Xin
Perennial ryegrass (Lolium perenne L.; Figure 1) is commonly used in turfgrass seed mixtures because of its rapid germination and establishment, traffic tolerance, and good turf quality. Unfortunately, perennial ryegrass also has an important weakness for turfgrass use in Minnesota: winter survival.
Previous research at the University of Minnesota has shown considerable genetic variation in winter hardiness and freezing tolerance among perennial ryegrass accessions. Controlled freezing studies have also shown that freezing tolerance is associated with survival under Minnesota field conditions (Hulke et al., 2007, 2008).
However, surviving winter may involve more than simply tolerating low temperatures. Winter also changes the developmental state of the plant. This leads to a question we would like to explore: Could the process that prepares perennial ryegrass to flower in spring also influence its ability to survive freezing temperatures?
Cold acclimation and vernalization
When temperatures decline in the fall, perennial ryegrass undergoes cold acclimation. Exposure to cool, nonfreezing temperatures triggers physiological and molecular changes that allow plants to tolerate lower freezing temperatures later in winter.
At the same time, prolonged exposure to cold also promotes vernalization. Vernalization is different from cold acclimation. Rather than directly increasing freezing tolerance, vernalization prepares the plant for flowering in the following spring when favorable growing conditions return.
Could these two processes be connected?
Research in temperate cereals suggests that cold acclimation and vernalization may be connected. The flowering-related gene VERNALIZATION1 (VRN1) has been associated with changes in freezing tolerance and the expression of cold-responsive genes (Dhillon et al., 2010). Whether a similar relationship occurs in perennial ryegrass is still unclear.
Our research
In our upcoming research, we plan to investigate how freezing tolerance in perennial ryegrass changes as plants progress through cold acclimation and vernalization. We are particularly interested in whether winter-hardy and winter-susceptible perennial ryegrass genotypes respond differently to prolonged cold exposure and whether completion of vernalization affects their ability to maintain freezing tolerance.
Understanding this relationship may provide another piece of the winter-hardiness puzzle and help identify perennial ryegrass germplasm better adapted to Minnesota and other northern climates.
References
Dhillon, T., Pearce, S. P., Stockinger, E. J., Distelfeld, A., Li, C., Knox, A. K., Vashegyi, I., Vágújfalvi, A., Galiba, G., & Dubcovsky, J. (2010). Regulation of freezing tolerance and flowering in temperate cereals: The VRN-1 connection. Plant Physiology, 153, 1846–1858.
Hulke, B. S., Watkins, E., Wyse, D., & Ehlke, N. (2007). Winterhardiness and turf quality of accessions of perennial ryegrass (Lolium perenne L.) from public collections. Crop Science, 47, 1596–1602.
Hulke, B. S., Watkins, E., Wyse, D. L., & Ehlke, N. J. (2008). Freezing tolerance of selected perennial ryegrass (Lolium perenne L.) accessions and its association with field winterhardiness and turf traits. Euphytica, 163, 131–141.