13C isotope discrimination variation in guar [cyamopsis tetragronoloba (L.) Taub.] under water-deficit conditions

Authors: MANLEY, AURORA - Texas A&M Agrilife; RAVELOMBOLA, WALTRAM - Texas A&M Agrilife; Adams, Curtis; SHRESTHA, RAJAN - Texas A&M University; HINSON, PHILIP - Texas A&M University; TROSTLE, CALVIN - Texas A&M Agrilife

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2025
Publication Date: 3/1/2025
Citation: Manley, A., Ravelombola, W., Adams, C.B., Shrestha, R., Hinson, P.O., Trostle, C. 2025. 13C isotope discrimination variation in guar [cyamopsis tetragronoloba (L.) Taub.] under water-deficit conditions. Agronomy. 16(1):31. https://doi.org/10.3390/ijpb16010031.
DOI: https://doi.org/10.3390/ijpb16010031

Interpretive Summary: Guar is a leguminous crop plant that is primarily cultivated for the "guar gum" contained in its seed. A notable feature of guar is its drought tolerance. The crop is grown in regions where this is important and guar breeders seek to improve the drought tolerance and water-use efficiency of new varieties. Studies in other crops have shown a relationship between carbon d13 isotope (C13) discriimination, which is a preference for assimilation of C13 over other C isotopes in plant growth, and water-use efficiency. The objective of this study was to determine if there is any relationship between these parameters in guar, so C13 discrimination could be used as a selection tool in guar breeding. Study results showed an increase in leaf C13 under drought stress and that drought-stressed plants differed in C13 among each other. Importantly, positive correlations were identified between C13 under drought and plant biomass production. These outcomes demonstrate that C13 discrimination has potential as a selection tool to identify drought-tolerant guar lines.

Technical Abstract: Guar is a legume cultivated for its high seed galactomannan content. India is the major guar producer globally and the U.S. has the largest guar market worldwide. Guar is drought-tolerant and suitable as a summer rotational crop in dryland farming systems. Studies have shown correlations between carbon d13 isotope (C13) discrimination and water-use efficiency in other crops. The objective of this study was to assess the variation in carbon d13 isotope discrimination among 30 guar accessions. Accessions were grown under greenhouse conditions in 3.79 L pots, including drought-stressed and wellwatered treatments. For each accession, beginning at the V5 to V8 growth stage, one pot was continuously irrigated, whereas irrigation was withheld from the other until wilting symptoms appeared after 50 days. Each treatment pair (well-watered/drought-stressed) was organized in a completely randomized design with three replications. Aboveground fresh and dry biomass data were collected, and the dry leaves were used for C13 isotope analysis. The results showed an increase in leaf C13 under drought stress. There were no differences among genotypes in C13 for well-watered plants (p = 0.63), but droughtstressed plants differed (p < 0.001). Significant positive correlations were identified between C13 under drought stress and the fresh (r = 0.70) and dry biomass (r = 0.68) of droughtstressed plants. These results demonstrate that C13 has potential as a criterion to identify drought-tolerant guar lines.