Location: Plant Genetic Resources Conservation Unit
Project Number: 6046-21000-013-044-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2024
End Date: Jul 31, 2025
Objective:
The ultimate goal of this project will be to develop adapted guar germplasm with improved guar gum content. The specific objectives are:
Objective 1. To evaluate guar gum content in the USDA germplasm
Specific Aim 1. To extract guar gum content from USDA guar germplasm seeds and evaluate guar gum using the megazyme assay procedure
Specific Aim 2. To identify the correlation between guar gum content and seed yield
Objective 2. To develop genomic resources for guar gum selection
Specific Aim 1. To conduct a genome-wide association study (GWAS) for guar gum content and guar seed yield
Specific Aim 2. To assess the accuracy of genomic selection in predicting guar gum content and seed yield
Approach:
Objective 1. To evaluate guar gum content in the USDA germplasm
A total of 250 United States Department of Agriculture (USDA) guar accessions obtained from Griffin, Georgia will be used for this project. These accessions were evaluated for seed yield and yield component during the summer of 2021 at the Cooperator's facilities in Vernon, TX and Lubbock, TX, respectively. These guar accessions will be re-evaluated during the summer of 2024 in the same locations (Vernon and Lubbock).
The study will be laid in a randomized complete design where each location will be considered as a blocking variable (2 locations, thus 2 replications/accession). At each location, each guar accession will be planted on a single row of 15 feet long and 40 inches spacing between rows. Plant spacing within row will be about 6 inches. Guar gum extraction from guar seeds will be conducted using the megazyme assay procedure, which is based on the approach. Guar gum evaluation will be conducted using a spectrophotometer set at 340 nm.
At each location, all guar pods from each plot will be hand harvested to avoid seed contamination between plots. Guar pods will be threshed using a belt thresher and the seeds will be weighted to calculate seed yield. The analysis of variance (ANOVA) will be conducted for seed yield. Pearson’s correlation coefficient between seed yield and guar gum content will be calculated to assess the relationship between gaur gum content and seed yield.
Objective 2. To develop genomic resources for guar gum selection
DNA extraction of the 250 USDA guar accession was completed in the Cooperator's lab. Whole-genome resequencing and DNA sequencing were performed. SNPs from whole genome resequencing will be used to conduct a population structure and genetic diversity analysis study. Population structure will be used to assess population stratification. Genetic diversity analysis will be combined to the population structure to assess how the two types of analysis are correlated. STRUCTURE 2.3.4 will be used to infer population structure. Population structure (K) analysis will be conducted using an admixture-based model along with a correlated allele frequency one, which will be independent for each run. For each estimated K value, 10 runs will be conducted and screened for optimal K values. Phylogenetic tree will be drawn using MEGA 7. Results including the Q groups from the population structure analysis will be used in MEGA 7 for a combined genetic diversity analysis. Least square means (LS Means) for guar gum content and seed yield will be used to conduct GWAS.
