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.
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.
1. To determine whether selecting for heavy seed improves germination and emergence in three cultivars of switchgrass.
We have completed two cycles of selection for heavy and light seed in switchgrass cultivars Timber, Carthage, and Brooklyn. In fall of 2011, cycle 1 and cycle 2 seed was harvested from plants in isolated crossing blocks and was dried, threshed, and stored. Cycle 1 and cycle 2 seed was germinated in early 2012 in the growth chamber, and germination was monitored daily for 28d. After repeating germination of all seed a second time, data was analyzed to determine the effectiveness of selection for heavy seed in improving switchgrass germination.
2. To develop cultivars with improved establishment without the use of herbicides.
In selecting for heavy switchgrass seed, we believe we are selecting for switchgrass plants with improved establishment that will be able to be planted without the use of herbicides. The final cycle of selection of this study was completed in 2011. Based on the results of this study, we believe that further cycles of selection need to be performed in order to further concentrate genes involved in superior germination and emergence. We also believe that dormancy is an important factor affecting switchgrass germination and must be accounted for in selection procedures. Therefore, we will continue selecting for heavy seed in cultivars Timber and Carthage (higher yielding cultivars than Brooklyn) as well as select individual plants that germinate rapidly given a very short after-ripening period (one to two weeks). Superior individuals will then be used for development of cultivars with improved establishment.
3. To disseminate results in the form field day seminars, a peer-reviewed journal article and fact sheets regarding switchgrass establishment.
The results of this experiment were shared as an oral presentation at the ASA, CSSA, and SSSA International Annual Meeting in Cincinnati, Ohio on October 23, 2012. A manuscript is currently being written that will be submitted for publication in a peer-reviewed journal (Global Change Biology Bioenergy). A fact sheet is also being prepared that summarizes the results of this study that will be available on the New Jersey Agricultural Experiment Station (NJAES) website as well as through NJAES county extension offices. Information learned from this study will be shared with growers and farmers via field day presentations in 2012. Finally, once selection procedures and adequate testing has been performed, we will release improved switchgrass cultivars.
Seed of three switchgrass cultivars, Timber, Carthage, and 9064202 (Brooklyn), was sorted with gravity deck into light and heavy classes. Unsorted seed was kept as a check. Three replicates of 100 seeds of all cultivars and weight classes were germinated in a growth chamber under the following conditions: 14H light at 25°C, 10H dark at 15°C, 75% relative humidity. Germination was monitored and recorded daily for 28d. Germinated seedlings were transplanted to pro-mix and kept in the greenhouse for 4 weeks. Seedlings were then transplanted to the field in isolated crossing blocks according to cultivar and weight class in spring of 2008. Plants were left in the field for one year to mature, and in the fall of 2009, seed was harvested from each isolated block and sorted again with gravity deck into heavy and light groups. This seed was then germinated in the growth chamber under the same conditions as above, and seedlings were transplanted to the greenhouse and then isolated blocks in the field in spring of 2010. In the fall of 2011, seed from all three cultivars was harvested from all isolated blocks (cycle 1, cycle 2, and unsorted check). Germination was monitored in the growth chamber as above, and germination percentage and germination rate index were calculated for all cultivars and weight classes (Figure 1). Data were analyzed using the Proc ANOVA procedure of the SAS statistical software program.
Selection for light seed resulted in lower germination percentages than unsorted in Brooklyn and Timber. However, germination percentages for heavy seed were not different than unsorted seed in all cultivars tested (Figure 2). As switchgrass is a highly heterogeneous species, further cycles of selection may be necessary to see gains in germination percentage in heavy seed. In addition, dormancy may be playing a role and may have a greater impact on seed germination percentage than seed weight.
Germination rate index increased in Brooklyn, remained the same in Carthage, and decreased in Timber after two cycles of selection for light seed (Figures 3-5). After two cycles of selection for heavy seed, germination rate indices were higher than the unsorted check in all cultivars tested (Figures 3-5).
The results of this study demonstrated that selection for heavy switchgrass seed via gravity deck over two cycles successfully improved germination rate in switchgrass cultivars Timber, Carthage, and Brooklyn. Seed separation via gravity deck is a simple and inexpensive method easily incorporated into current breeding programs that can improve germination rates in switchgrass. While overall germination percentage did not improve with two cycles of selection for heavy seed, this information demonstrated that the factor of seed weight alone is not a sufficient selection criterion for improving switchgrass seed germination percentage. Upon further testing involving a cold stratification treatment to alleviate the affects of dormancy, we believe that dormancy is a significant factor involved in poor switchgrass germination and establishment and must be considered when determining selection procedures for improving germination in switchgrass. Based on these discoveries, we have adjusted our selection criteria to include dormancy as a factor involved in germination and will continue selecting for improved germination and emergence in switchgrass cultivars Timber and Carthage. Once we have sufficiently tested our progeny, we will release new cultivars of switchgrass with improved germination and emergence. Adoption of these improved cultivars has the potential to reduce environmental and health risks in agriculture from a reduction in herbicide use on farms. The development of new cultivars should also increase productivity and reduce establishment costs (the majority of the costs associated with growing switchgrass), which should lead to an increase in net farm income. The utilization of these switchgrass cultivars should improve the quality of life for farmers and the community, and ultimately help farmers become more profitable, be good stewards of the land and help strengthen the community.
Education & Outreach Activities and Participation Summary
The results of this experiment were shared as an oral presentation at the ASA, CSSA, and SSSA International Annual Meeting in Cincinnati, Ohio on October 23, 2012. Other plant breeders were present, and questions and discussion of the results followed the presentation. A manuscript is currently being written that will be submitted for publication in a peer-reviewed journal (Global Change Biology Bioenergy). This publication targets other plant biologists and plant breeders, who can use the knowledge presented in their research. A fact sheet is also being prepared that summarizes the results of this study that will be available on the New Jersey Agricultural Experiment Station (NJAES) website as well as through NJAES county extension offices. Information learned from this study was to be shared with growers and farmers via field day presentations in 2012. Unfortunately one of the field days was cancelled due to rain and not rescheduled. The organizers of the second field day (a forage and grain producers field day), decided to eliminate the bioenergy portion of the program completely, and therefore the results of the study were not able to be shared. Finally, once selection procedures and adequate testing has been performed, we will release improved switchgrass cultivars.
Economic analysis was not a goal of this project and was therefore not completed.
Because we did not work directly with farmers on this project, there is no actual outcome to report here. However, based on conversation with farmers, they will readily utilize switchgrass cultivars with improved germination and establishment once they are released.
Areas needing additional study
While switchgrass germination rate improved with two cycles of selection for heavy seed, the selection criteria utilized here (seed weight alone) was not sufficient to significantly improve overall germination percentage in the three switchgrass cultivars tested in this study. After no gain from selection for seed weight was realized after one cycle, a cold stratification treatment was added to the final comparison to investigate the affects of dormancy on switchgrass germination. A brief analysis of the cold-stratified seed demonstrated that seed weight was not a significant factor in germination percentage. Therefore, we believe that dormancy plays a larger role in switchgrass seed germination than seed weight in the cultivars tested here. Further testing is needed to determine the affects of selecting for both heavy seed and seed with low dormancy levels.
- Figure 2 Germination percentages in 3 switchgrass cultivars after 2 cycles of selection for heavy and light seed
- Figure 3 Germination rate index in Brooklyn switchgrass seed after 2 cycles of selection for heavy and light seed
- SARE Final report references
- Figure 1 Selection Flow Chart
- Figure 4 Germination rate indices in Carthage switchgrass seed after 2 cycles of selection for heavy and light seed
- Figure 5 Germination rate indices in Timber switchgrass seed after 2 cycles of selection for heavy and light seed