Evaluating USDA guar [Cyamopsis tetragonoloba (L.) Taub.] germplasm for seed protein content

Guar [Cyamopsis tetragonoloba (L.) Taub] is a legume primarily grown for the guar gum in its endosperm, which is used in industrial, chemical, and food applications. Guar seed also contains protein, though this aspect of the crop has been much less studied. The high protein content makes it a good livestock feed source and the tender pods a nutritious vegetable for humans. The objective of this study was to evaluate seed protein content of diverse guar germplasm accessions sourced from the United States Department of Agriculture (USDA) plat germplasm repository. A two-year field study was conducted at Chillicothe and Lubbock, Texas, in 2021 and 2022. Nitrogen combustion analysis was used to evaluate protein content on ground seed samples and data was analyzed using JMP Genomics ® 7 (SAS Institute, Inc.). Significant location X year X genotype interaction (P-value < 0.05) and main genotype effects (P-value < 0.05) were identified for seed protein content. Broad-sense heritability (H) for protein content was 80.7%, indicating that most variation was due to genetics and the trait is selectable in breeding. A total of 10 guar genotypes had 0.5% higher protein content, across all locations and years, than the check genotype ‘Santa Cruz’. These findings identify high seed protein guar lines that can be used as parents in guar breeding and contribute basic knowledge on factors affecting seed protein in the crop.