Does divergent selection for seedling tiller number in big bluestem and switchgrass result in biomass yield and quality differences in mature grass swards?

Authors: Mitchell, Robert - Rob; Vogel, Kenneth; TUNNELL, SUSAN - University Of Nebraska; STUBBENDIECK, JIM - University Of Nebraska

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2023
Publication Date: 11/9/2023
Citation: Mitchell, R., Vogel, K.P., Tunnell, S., Stubbendieck, J. 2023. Does divergent selection for seedling tiller number in big bluestem and switchgrass result in biomass yield and quality differences in mature grass swards?. Crop Science. 14(11):1223-1234. https://doi.org/10.4236/ajps.2023.1411083.
DOI: https://doi.org/10.4236/ajps.2023.1411083

Interpretive Summary: Improving perennial grasses like big bluestem and switchgrass for yield, digestibility, or other selected traits requires multiple generations and extensive field evaluation. Recent big bluestem cultivars required nearly 20-years from initiation to cultivar release. Selecting for traits in the seedling stage could accelerate perennial grass cultivar development. Our objective was to determine if breeding for tiller mass and number in the seedling stage for big bluestem and switchgrass would result in changes in biomass yield and quality when grown in seeded stands. Breeding for seedling tiller mass and number in big bluestem and switchgrass was not an effective method for improving yield or quality when grown in competitive stands. Although the big bluestem and switchgrass populations did have differences in tiller number when grown in space-planted nurseries, these genetic differences did not result in increased yield in seeded stands. The results indicate that when a stand density threshold is achieved for seeded stands of big bluestem and switchgrass, genetic tillering potential has limited affect on yield, and other traits such as tiller height and mass are more important drivers of yield. These results clearly demonstrate the importance of evaluating perennial grasses in seeded trials and not relying solely on greenhouse-grown plants or space-planted nurseries to make selection decisions.

Technical Abstract: Breeding for seedling traits in perennial grasses that translate into increased biomass yield or quality in established swards could accelerate the development of perennial grass cultivars for bioenergy or forage. In previously reported research, breeding for single large tillers (ST) or multiple tillers (MT, >3) six weeks after planting for two generations in big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) base populations produced ST and MT populations that differed significantly for seedling and mature plant traits including biomass yield in spaced planted nurseries. Our objective was to evaluate these ST and MT populations in sward trials to determine the effect of these genetic changes on biomass yield and quality when the plants were grown in competitive sward conditions. Big bluestem monocultures of the base, ST, and MT populations were evaluated at three locations in Nebraska in 2001 and 2002 as randomized complete block experiments with four replicates. Switchgrass monocultures of the base, ST, and MT populations were evaluated in 2003, 2004, and 2005 near Mead, NE as a randomized complete block with six replicates. In both big bluestem and switchgrass, the ST and MT populations did not consistently differ from the base population or each other for biomass yield or forage quality. These results demonstrate the importance of evaluating perennial grasses in sward trials and not relying solely on greenhouse-grown plants or space-planted nurseries to develop selection criteria and to make selection decisions.