Evaluation of nodule traits in USDA guar genotype accessions

Authors: MALANI, SHUBHAM - Texas A&M University; RAVELOMBOLA, WALTRAM - Texas Agrilife Research; Adams, Curtis; IBRAHIM, AMIR - Texas A&M University; ALE, SRINIVASULU - Texas Agrilife Research

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2024
Publication Date: 7/6/2024
Citation: Malani, S., Ravelombola, W., Adams, C.B., Ibrahim, A., Ale, S. 2024. Evaluation of nodule traits in USDA guar genotype accessions. Euphytica. 220(8):1-13. https://doi.org/10.1007/s10681-024-03378-3.
DOI: https://doi.org/10.1007/s10681-024-03378-3

Interpretive Summary: Guar is a nitrogen-fixing legume crop with drought- and heat-tolerance. The variation among guar varieties in nitrogen-fixing traits is largely unknown, however, which prevents progress in breeding for improved lines. The objective of this study was to generate such knowledge using a large collection of USDA guar variety accessions (225) in a greenhouse pot study. Results showed that plant height, average nodule diameter, and plant dry biomass varied significantly among varieties, but there were not significant differences for nodule number and nodule weight per plant. Broad-sense heritability was high for average nodule diameter, nodule weight per plant, and plant biomass production, indicating that these traits are selectable in plant breeding. This is promising, since selection for high values in these traits would be expected to increase nitrogen fixation and yield. The results also revealed promising guar accessions that can be useful in guar breeding initiatives. Overall, this research will help plant breeders enhance guar nodulation, nitrogen fixation, and yield by utilizing the scientific knowledge and superior germplasm obtained through this study.

Technical Abstract: Guar [Cyamopsis tetragonoloba (L.) Taub] is an annual diploid legume (2n = 2x= 14)crop and is drought and heat tolerant. This crop is primarily grown for the large amount of galactomannan gum that is present in the seed endosperm and it can improve ecosystem services by fixing atmospheric nitrogen. However, the genetics of guar nodulation remains poorly understood. Therefore, the objective of this study was to assess the variation of nodule and plant growth traits in a set of guar germplasm. A total of 225 United States Department of Agriculture (USDA) guar accessions were evaluated for nodule traits in three runs in a greenhouse. Results showed that plant height, average nodule diameter, and plant dry biomass varied significantly among genotypes (p-values<0.05). However, no significant differences among genotypes were found for nodule number per plant, fresh/dry nodule weight per plant, and fresh plant biomass. Broad-sense heritability was high for average nodule diameter, nodule weight per plant, and plant biomass production, indicating that genetic gain in these traits can be attained through the plant breeding process. This is promising, since selection for high values in these traits would be expected to increase nitrogen fixation and yield. There were strong positive and significant correlations between nodule number and both fresh and dry nodule weights (r=0.79 and 0.71, respectively). The results also revealed several promising guar accessions that can be useful in guar breeding initiatives. Overall, this research will help breeders enhance guar nodulation, nitrogen fixation, and yield by utilizing the scientific knowledge and superior germplasm obtained through this study.