Texas Little Bluestem (Schizachyrium scoparium) Phenotypic Attribute Correlations to Collection Site Environment Characteristics

1. 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. 

2. 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).

3. 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.

4. 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.

5. 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.