Switchgrass is a prominent bioenergy crop. Like most perennial warm season species, switchgrass undergoes growth suspension in winter as a surviving strategy in temperate climates to protect their meristems from cold injuries and dehydration, while storage organs below ground drive spring regrowth when conditions become favourable. In this paper, we describe a reliable phenotyping method for winter dormancy in switchgrass using various traits including regrowth height after clipping in early fall (FRH), senescence percentage, date of spring regrowth (SRD), and flowering date (FD). FRH and senescence percentage appear to be reliable indicators of the onset of winter dormancy, whereby accessions that initiated dormancy early have a low FRH and a high senescence percentage. Even though it is difficult to have an exact assessment of the duration of dormancy because it is hard to determine with precision the date of growth suspension, SRD can be used as a surrogate indicator of the duration. Flowering date showed low correlations with all the traits and biomass yield suggesting that it may not be a reliable indicator for winter dormancy in switchgrass. Combining the variables FRH, senescence, and SRD in a selection index may provide a reliable tool to phenotype winter dormancy in switchgrass. The strong correlation of these variables with biomass yield makes them useful candidates for the manipulation of the duration of dormancy to increase the growing season and consequently improving biomass production. In southern regions with mild winters, it might be possible through intense selection to develop germplasm with much reduced dormancy or even non-dormant switchgrass germplasm.
Romberger, J.A. (1963) Meristems, Growth and Development in Woody Plants: An Analytical Review of Anatomical, Physiological, and Morphogenic Aspects. Technical Bulletin No. 1293, United States Department of Agriculture, Forest Service.
Schoot, C.V.D. (1996) Dormancy and Symplasmic Networking at the Shoot Apical Meristem. In: Lang, G.A., Ed., Plant Dormancy: Physiology, Biochemistry and Molecular Biology, CAB International, Wallingford, 59-81.
Vegis, A. (1964) Dormancy in Higher Plants. Annual Review of Plant Physiology, 15, 185-224. https://doi.org/10.1146/annurev.pp.15.060164.001153
Rohde, A. and Bhalerao, R.P. (2007) Plant Dormancy in the Perennial Context. Trends in Plant Science, 12, 217-223. https://doi.org/10.1016/j.tplants.2007.03.012
Thomashow, M.F. (1999) Plant Cold Acclimation: Freezing Tolerance Genes and Regulatory Mechanisms. Annual Review of Plant Physiology & Plant Molecular Biology, 50, 571-599. https://doi.org/10.1146/annurev.arplant.50.1.571
Preston, J.C. and Sandve, S.R. (2013) Adaptation to Seasonality and the Winter Freeze. Frontiers in Plant Science, 4, 167-167. https://doi.org/10.3389/fpls.2013.00167
Lang, G.A., Early, J.D. Martin, G.C., and Darnell, R.L. (1987) Endo-, Para-, and Ecodormancy: Physiological Terminology and Classification for Dormancy Research. HortScience, 22, 371-377.
Junttila, O. (1988) To Be or Not to Be Dormant: Some Comments on the New Dormancy Nomenclature. HortScience, 23, 805-806.
Lang, G.A. (1987) Dormancy: A New Universal Terminology. HortScience, 22, 817-820.
Woo, H.R., Kim, H.J., Nam, H.G. and Lim, P.O. (2013) Plant Leaf Senescence and Death-Regulation by Multiple Layers of Control and Implications for Aging in General. Journal of Cell Science, 126, 4823-4833. https://doi.org/10.1242/jcs.109116
Anderson, J.V., Gesch, R.W., Jia, Y., Chao, W.S. and Horvath, D.P. (2005) Seasonal Shifts in Dormancy Status, Carbohydrate Metabolism, and Related Gene Expression in Crown Buds of Leafy Spurge. Plant, Cell and Environment, 28, 1567-1578. https://doi.org/10.1111/j.1365-3040.2005.01393.x
Sarath, G., Baird, L.M. and Mitchell, R.B. (2014) Senescence, Dormancy and Tillering in Perennial C4 Grasses. Plant Science, 217-218, 140-151. https://doi.org/10.1016/j.plantsci.2013.12.012
Horvath, D.P., Anderson, J.V., Chao, W.S. and Foley, M.E. (2003) Knowing When to Grow: Signals Regulating Bud Dormancy. Trends in Plant Science, 8, 534-540. https://doi.org/10.1016/j.tplants.2003.09.013
Casler, M.D., Stendal, C.A., Kapich, L. and Vogel, K.P. (2007) Genetic Diversity, Plant Adaptation Regions, and Gene Pools for Switchgrass. Crop Science, 47, 2261-2273. https://doi.org/10.2135/cropsci2006.12.0797
Christensen, C.A. and Koppenjan, G. (2010) Planting and Managing Switchgrass as a Dedicated Energy Crop, 2nd Edition. Blade Energy Crops, Kluwer, CERES Inc., Los Angeles, CA.
Lowry, D.B., Behrman, K.D., Grabowski, P., Morris, G.P., Kiniry, J.R. and Juenger, T.E. (2014) Adaptations between Ecotypes and Along Environmental Gradients in Panicum virgatum. American Naturalist, 183, 682-692. https://doi.org/10.1086/675760
Casler, M. (2012) Switchgrass Breeding, Genetics, and Genomics. In: Monti, A., Ed., Switchgrass, Springer, London, 29-53. https://doi.org/10.1007/978-1-4471-2903-5_2
Aspinwall, M.J., Lowry, D.B., Taylor, S.H., Juenger, T.E., Hawkes, C.V., Johnson, M.V.V., Kiniry, J.R. and Fay, P.A. (2013) Genotypic Variation in Traits Linked to Climate and Aboveground Productivity in a Widespread C4 Grass: Evidence for a Functional Trait Syndrome. New Phytologist, 199, 966-980. https://doi.org/10.1111/nph.12341
Kszos, L.A., Downing, M.E., Wright, L.L., Cushman, J.H., McLaughlin, S.B., Tolbert, V.R., Tuskan, G.A. and Walsh, M.E. (2000) Bioenergy Feedstock Development Program Status Report. Publication No. 5049, Environmental Sciences Division, Oak Ridge, TN.
McLaughlin, S.B. and Kszos, L.A. (2005) Development of Switchgrass (Panicum virgatum) as a Bioenergy Feedstock in the United States. Biomass and Bioenergy, 28, 515-535. https://doi.org/10.1016/j.biombioe.2004.05.006
Parrish, D.J. and Fike, J.H. (2005) The Biology and Agronomy of Switchgrass for Biofuels. Critical Reviews in Plant Sciences, 24, 423-459. https://doi.org/10.1080/07352680500316433
United States Department of Agriculture (2016) U.S. National Plant Germplasm System. https://www.ars-grin.gov/npgs/collections.html
Acharya, A.R. (2014) Genetic Diversity, Population Structure and Association Mapping of Biofuel Traits in Southern Switchgrass Germplasm. Ph.D. Dissertation, University of Georgia, Georgia.
Your Weather Service (2017) U.S. Climate Data. https://www.usclimatedata.com/
U.S. Naval Observatory (2011) Astronomical Applications Department. http://aa.usno.navy.mil/index.php
Lamari, L. (2008) Assess 2.0. Image Analysis Software for Plant Disease Quantification. APS Press, St. Paul, MN.
Trimble Ag Field Solutions (2017) GreenSeeker Handheld Crop Sensor. https://agriculture.trimble.com/precision-ag/products/greenseeker/
Benedict, H.M. (1940) Effect of Day Length and Temperature on Flowering and Growth of Four Species of Grasses. Journal of Agricultural Research, 61, 661-671.
Adler, P.R., Sanderson, M.A., Boateng, A.A., Weimer, P.J. and Jung, H.J.G. (2006) Biomass Yield and Biofuel Quality of Switchgrass Harvested in Fall or Spring. Agronomy Journal, 98, 1518-1525. https://doi.org/10.2134/agronj2005.0351
Johnson, J.M.F. and Gresham, G.L. (2014) Do Yield and Quality of Big Bluestem and Switchgrass Feedstock Decline Over Winter? BioEnergy Research, 7, 68-77. https://doi.org/10.1007/s12155-013-9349-9
Gamble, J.D., Jungers, J.M., Wyse, D.L., Johnson, G.A., Lamb, J.A. and Sheaffer, C.C. (2015) Harvest Date Effects on Biomass Yield, Moisture Content, Mineral Concentration, and Mineral Export in Switchgrass and Native Polycultures Managed for Bioenergy. BioEnergy Research, 8, 740-749. https://doi.org/10.1007/s12155-014-9555-0
McMillan, C. and Weiler, J. (1959) Cytogeography of Panicum virgatum in Central North America. American Journal of Botany, 46, 590-593. https://doi.org/10.1002/j.1537-2197.1959.tb07057.x
Van Esbroeck, G.A., Hussey, M.A. and Sanderson, M.A. (2003) Variation between Alamo and Cave-in-Rock Switchgrass in Response to Photoperiod Extension. Crop Science, 43, 639-643.
Wayman, S., Bowden, R.D. and Mitchell, R.B. (2014) Seasonal Changes in Shoot and Root Nitrogen Distribution in Switchgrass (Panicum virgatum). BioEnergy Research, 7, 243-252. https://doi.org/10.1007/s12155-013-9365-9
Wilson, D.M., Heaton, E.A., Liebman, M. and Moore, K.J. (2013) Intraseasonal Changes in Switchgrass Nitrogen Distribution Compared with Corn. Agronomy Journal, 105, 285-294. https://doi.org/10.2134/agronj2012.0233
Ashworth, A.J., Allen, F.L., Bacon, J.L., Sams, C.E., Hart, W.E., Grant, J.F., Moore Jr., P.A. and Pote, D.H. (2017) Switchgrass Cultivar, Yield, and Nutrient Removal Responses to Harvest Timing. Agronomy Journal, 109, 2598-2605. https://doi.org/10.2134/agronj2017.01.0018