Salinity responses in 24 guar genotypes are linked to multigenic regulation explaining the complexity of tolerance mechanisms in planta

Authors: Sandhu, Devinder; PALLETE, ANDREW - University Of California, Riverside; WILLIAM, MARIA - University Of California, Riverside; Ferreira, Jorge; KAUNDAL, A - Utah State University; GROVER, KULBHUSHAN - New Mexico State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2022
Publication Date: 10/31/2022
Citation: Sandhu, D., Pallete, A., William, M., Ferreira, J.F., Kaundal, A., Grover, K.K. 2023. Salinity responses in 24 guar genotypes are linked to multigenic regulation explaining the complexity of tolerance mechanisms in planta. Crop Science. 63(2):585-597. https://doi.org/10.1002/csc2.20872.
DOI: https://doi.org/10.1002/csc2.20872

Interpretive Summary: Guar is a low-input, drought-tolerant legume crop where the whole plant is used for forage, pods are used as a vegetable, and seed has several commercial applications. Arid conditions, continuing drought, low-quality irrigation water, and economic value make guar an attractive crop for cultivation in the American Southwest. Although guar is tolerant to abiotic stresses such as drought and heat, little is known about its salinity responses. This investigation focused on screening guar germplasm for salinity tolerance and understanding the genetic networks involved in plant responses to salinity stress. Evaluation of 24 diverse guar genotypes under salinity indicated significant genetic variation for salinity tolerance and led to the identification of several salt-tolerant genotypes. Our results showed that guar plants could effectively regulate the movement of sodium from root to shoot; however, the movement of chloride is not well regulated. The expression analysis suggested that various component traits of the salinity tolerance mechanisms, including sodium exclusion, chloride exclusion, and tissue tolerance, are crucial during salinity stress in guar. This information will be useful to guar breeders in developing new salt tolerant varieties with multiple component traits for salinity tolerance.

Technical Abstract: Guar (Cyamopsis tetragonoloba (L.) Taub.) is an economically important, drought-tolerant legume crop affected by moderate to high salinity. Guar has various industrial applications, including gum extracted from seeds that is widely used in the oil and natural gas industries. In this investigation, we evaluated the salinity tolerance of different guar genotypes and their relation to genetic mechanisms regulating guar responses to salinity stress. We screened 24 guar genotypes in a greenhouse lysimeter system under control (electrical conductivity (EC) = 1.46 dS m-1) and high salinity (EC = 13.65 dS m-1) treatments. Both length and biomass of shoots were significantly affected by salinity compared to roots, indicating higher shoot than root sensitivity to salinity. Twenty-four genotypes were classified based on salt tolerance index for each trait. Tissue ion analysis revealed that roots accumulated over 10-fold higher Na than leaves, demonstrating that guar effectively regulated the root-to-shoot movement of Na+. However, higher Cl concentrations in leaves than roots indicated less regulatory control of Cl- movement. Based on the morphological traits and tissue ion analysis, six genotypes (PI 164486, PI 253186, PI 26152, PI 158125, PI 179926, and PI 263698) with different responses to salinity were selected for gene expression analysis. Expression patterns of different genes showed that a complex network of component traits, including Na+ exclusion, Cl- exclusion, and tissue tolerance, regulate salinity tolerance in guar. Hence, the genetic information about different component traits will benefit guar breeders in developing new varieties that are more tolerant to salinity than current ones.