Improving the Sustainability of Switchgrass Establishment Through the Development of Cultivars with Improved Germination

Switchgrass (Panicum virgatum L.) is a C4 perennial warm-season grass native to the eastern two-thirds of the United States and chosen as a model bioenergy feedstock species by the Department of Energy due to its high productivity across a wide geographic range, suitability for marginal land, low water and nutrient requirements, and positive environmental benefits. However, poor germination resulting in slow and inconsistent establishment and heavy weed competition is a major limitation to the successful adoption of this bioenergy crop. Currently, herbicide applications are used to reduce weed competition during the establishment period and unfortunately do not completely guarantee successful stand establishment. It has been demonstrated that larger and heavier switchgrass seed has improved germination and emergence, and that selecting for high seed weight in switchgrass increased seed weight in progeny (Aiken and Springer, 1995; Boe & Johnson, 1987).
The purpose of this project was to select switchgrass for heavier seed (compared to lighter seed) in an effort to improve germination, seedling vigor and stand establishment without the use of herbicides. A gravity deck was used to separate seed of three switchgrass cultivars into heavy and light weight classes for two cycles of selection. Three replicates of seed from all selection cycles were germinated in a growth chamber for 28 d and compared for germination and emergence to determine if selection for heavy seed improves germination in switchgrass. Germination percentages for heavy seed were not different than unsorted seed in all cultivars tested. Further cycles of selection for heavy seed may be necessary to improve germination in switchgrass, and other factors such as dormancy may need to be considered when determining selection procedures for improving germination. While overall germination percent did not improve with selection, germination rates were higher after two cycles of selection for heavy seed in all cultivars tested. The selection method used in this study is a simple, inexpensive way for breeders to improve germination rate in switchgrass.

Introduction:

Switchgrass (Panicum virgatum L.) is a C4 perennial warm-season grass native to the eastern two-thirds of the United States and chosen as a model bioenergy feedstock species by the Department of Energy. Switchgrass has several attributes that make it a sustainable bioenergy crop and led to its designation as a model bioenergy species by the Department of Energy. First, it is native to most of the US and is therefore not likely to become invasive. Switchgrass is also productive over a wide geographic range and can grow on marginal land not suitable for traditional agricultural crops. It is therefore not meant to compete with food production but to return marginal farmland back into production, which should improve farm productivity, sustainability, and increase net income.
As a perennial crop, switchgrass is advantageous over annual crops (like corn for bioenergy) because it does not need to be replanted every year. This results in reduced risk of soil erosion and runoff, less fossil fuel inputs and, improved soil quality (Sanderson et al., 1996). In addition to the large amount of above-ground biomass produced, switchgrass has an extensive and deep root system that is beneficial for increasing soil carbon storage (sequestration) and is 50% more effective in water use compared to cool-season grasses (Stout et al., 1988). Switchgrass has also been shown to improve surface water quality by filtering phosphorous and nitrogen from runoff (Lee et al., 1998). Another advantage of switchgrass is that it is a low input crop with low water, fertility, and pesticide requirements. In addition, switchgrass provides a suitable habitat for threatened grassland birds (Murray et al., 2003). Lastly, estimated greenhouse gas emissions from switchgrass-derived ethanol are 94% lower than those estimated from gasoline (Schmer et al., 2008). The use of switchgrass on farms can dramatically improve the sustainability of farming practices and provide a domestic biofuel source. This project has the potential to reduce environmental and health risks in agriculture from a reduction in herbicide use on farms and by using a sustainable crop species like switchgrass.

The purpose of this project was to determine whether emergence, germination, and stand establishment of switchgrass can be improved by selecting for heavy seed. Switchgrass is emerging as a bioenergy crop, but it has very poor germination resulting in slow and inconsistent establishment (Aiken and Springer, 1995; McLaughlin and Kszos, 2005). In fact, the inability to produce rapid and consistent stands of switchgrass is one of the major constraints to growing switchgrass as an economically viable bioenergy crop. Currently, herbicides are recommended and typically required to reduce weed populations that outcompete switchgrass seedlings during the establishment period (McLaughlin and Kszos, 2005). However, the use of herbicides does not guarantee that switchgrass will establish successfully, especially in marginal soils. In order to increase the profitability and sustainability of switchgrass production for farmers, research is needed to develop switchgrass varieties with improved germination, emergence, and stand establishment.
In previous research, Aiken and Springer (1995) demonstrated that germination and emergence increased as seed size increased in six switchgrass cultivars. Boe and Johnson (1987) suggested seed cleaning and breeding for large seeded cultivars as two possible methods for improving switchgrass establishment. They demonstrated that selection for high seed weight was effective in increasing seed weight of progeny from a bulk seed lot in an open pollinated field. However, no studies have been conducted that investigate the effects of several cycles of selection for seed weight on switchgrass germination and emergence nor have improved cultivars resulted from such selection efforts. We hypothesize that seed germination and emergence will improve with cycles of selection for heavier seed in switchgrass, while germination and emergence will decrease with cycles of selection for lighter seed. We are hopeful that this innovative selection technique will result in new switchgrass cultivars with improved germination that will not require the use of herbicides. The development of switchgrass varieties with improved establishment will result in an overall reduction in herbicide use that will lower production costs and increase crop productivity and net farm income. Additionally, a reduction in herbicide use will improve soil conservation and water quality and reduce human health risks.