Final report for GS20-227
There is little knowledge about the phenotypic variation within little bluestem (Schizachyrium scoparium) (LBS) accessions collected throughout Texas. A better understanding of the relationship between phenotypic characteristics of our current collection as well as commercial releases and their original collection site characteristics would help guide future ecotypic releases. We have a Texas Native Seed (TNS) collection that encompasses regional diversity, but we are unsure of its genetic variability as expressed in a single environment. We hypothesize that LBS within that collection will show phenotypic differences corresponding with their geographical origin, namely edaphoclimatic variability as well as latitude and longitude. Our study will address two objectives in relation to accession origin: 1. determine the plant nutrient value at inflorescence and post-frost; and 2. evaluate plant physiological characteristics, especially flowering date, at inflorescence and post-frost. We will incorporate a parallel RADseq study to map geographical ecotypes. Having a better understanding of nutritive value and physiological characteristics at inflorescence and post-frost as these relate to the original germplasm genetics as well as collection site characteristics such as soil, climate and historical management will guide future restoration projects as they select for ecotypic variation within the TNS LBS collection.
This project will consist of two objectives for the TNS LBS accession collection as well as currently sold releases as they relate to original site collection characteristics: 1. Determine the plant nutrient value at inflorescence and post-frost and relate it to original germplasm collection environment. 2. Evaluate plant physiological characteristics at inflorescence and post-frost and correlate it to the original germplasm collection environment.
- Experimental design
Accessions were collected from 2002 to 2012 across Texas from longitudes 97°21’ to 101°15’ latitudes 29°55’ to 34°15’. Twelve commercially available LBS releases were included as comparisons (NRCS 2016 and NRCS 2017). The study will take place at the Texas A&M AgriLife Research Center located in Stephenville Texas 32°15’11” N, 98°11’33” W. Annual average monthly temperatures range from 10.8 to 24.3°C with an annual average of 17.6°C (World Climate 2020). Precipitation averages 800 mm year1 (World Climate 2020). I will use established LBS accessions arranged in a randomized complete block design, with each entry replicated twice (Karn and Tober 1990). Block design compensated for soil environmental differences in the field. The experiment unit will consist of the average of all 10 plants in each row. Each plant will be placed 30 cm apart with 90 cm between rows. The site was only given supplemental irrigation during 2016, the establishment year, and kept clean of weeds as recommended by Karn and Tober (1990) for germplasm evaluations. In June 2020, two plants from each replicated accession will be collected at vegetative stage before tiller growth, described as the clipped treatment. After the first frost four plants from each replicated accession will be collected, two from the June-clipped treatment and two previously unclipped. All tillers from each plant will be clipped 3 cm above the soil.
- Nutritive value (1)
I will determine dry matter yield (DMY) of two plants in each row in June and four at post frost, the latter consisting of two previously unharvested and two regrowth from the June harvest. This will entail harvesting all tillers at 10 cm above soil surface. This material will be dried in a forced-air oven at 55°C until weight loss ceases. The dried material will be ground through a 1-mm screen in a Thomas Wiley Laboratory Mill Model 4 (Thomas Scientific LLC, Swedesboro, New Jersey) and used to determine carbon (C), nitrogen (N), in-vitro dry matter digestibility (IVDMD) and plant fiber fractions. Total C and N content will be determined by combustion in a LECO CN-828 (LECO, St. Joseph, Michigan). I will determine IVDMD using an ANKOM Daisy Incubator (ANKOM Technology, Macedon, New York) based on methodology modified from Lowery (1969). Neutral detergent fiber (NDF), acid detergent fiber (ADF) and ADF lignin (ADL) fiber fractions will be assayed using an ANKOM 200 Fiber Analyzer (ANKOM technology, Macedon, New York) according to modified methods first described by Van Soest and Robertson (1980).
- Physiological characteristics (2)
I will determine date of initial boot, flowering, seed set, tiller density, height and the basal circumference. Initial boot date will be documented following the procedure established by Karn and Tober (1990. Boot, flowering and ripe seed dates will be recorded starting at June 2019 collection till the first frost date. Tiller density will consist of counting the tillers of each individual plant (Derner et al. 2004). The height of each plant will be measured starting at the base of the plant to the top of the highest point of the tallest inflorescence (Derner et al. 2004 and Springer 2012). Basal circumference will consist of measuring around the base of each plant and recording an average (Derner et al. 2004). Tiller density, height and basal circumference will be recorded after the first frost date when the whole plant is collected from both clipped and unclipped treatments.
- Statistical analyses
This is a two-factorial experiment in which independent variables will include accession and, in some cases, harvest date. Independent variables for the two-factorial portion will include the 54 accessions and two seasons. Data will be submitted to analyses of variance using Statistical Analysis System (SAS, Cary, North Carolina) once data normal distribution is verified or transformed if necessary. Multiple mean separation where appropriate, will be carried out using a least significant mean difference. Analysis of variance for the two-factor portion of the experiment will first determine interactions between each independent variable. If no interaction is found, I will look at the simple effects of each factor on the dependent variables. Multiple mean separation using a least significant mean difference will be used to group accessions into means which are different from each other. Finally, probability levels at any difference equal to or less than 5% (P 0.05) will be considered significant and not reported. Any P > 0.05 will be reported in the results and discussion.
- RADseq study
Although not directly related to this project, I will provide these data to Dr. Jeff Brady, plant geneticist at Texas A&M AgriLife Research, who is currently running a RADseq study on this same collection. These data will allow him to map ecotypic adaptation regions within the southern Great Plains and indicate which accessions to provide to commercial seed companies for commercial development.
The results that were achieved in this study was that little bluestem was influenced by different harvest regimens. Statistical analysis was done through R-studio where ANOVAs were used to determine if there was significance.
Educational & Outreach Activities
This research was presented at the 2020 Texas Plant Conservation Conference. At this conference graduate student Kimberlee Howell won best poster presentation. At the Texas Plant Conservation Conference the physiological characteristics were focused on. This research was also presented at the American Society of Agronomy, the Crop Science Society of America, and the Soil Science Society of America Conference. At this conference the nutritional characteristics were discussed.
We are currently working on analyzing samples in the lab for year two. Once year two samples have been completed we will run statistical analysis to determine if differences in phenotypes and original geographic information are connected.
During the course of this project our knowledge has changed. Due to time restrictions the thesis objectives had to change to how little bluestem phenotypes were influenced by different harvest regimens. We discovered that little bluestem was influenced by being harvested during the growing season.
For future studies I would recommend that little bluestem or other native species are evaluated at different locations throughout the state. This will help increase the understanding of how these species are influenced by different environmental characteristics.