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

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.