Seedling emergence of guar (Cyamopsis tetragonoloba L.) genotypes and their growth under irrigation water salinity

Salinity and water scarcity are threatening the sustainability of agriculture in the arid regions of the world. There is an urgent need to develop information on suitable crops that can tolerate salinity and drought to ensure the long-term viability of agriculture in these regions. Guar (Cyamopsis tetragonoloba L.) is considered a salt- and drought-tolerant crop that is economically viable. This study was conducted to evaluate the tolerance of 25 guar genotypes under three irrigation water salinities (3.0, 6.0, and 9.0 dS m⁻¹) at Sindh Agriculture University, Tandojam, Pakistan. Twenty-five seeds of each genotype were sown in sand-filled pots, irrigated with 1.5 L of treatment water, and arranged according to a split-plot design with three replications. Genotypes were categorized into four groups based on salinity tolerance index (STI) values of seedling emergence and composite biomass of shoot and root, and considered tolerant (>0.75), moderately tolerant (0.51–0.75), moderately sensitive (0.26–0.50), and sensitive (≤0.25) at various salinity levels. Across all genotypes, shoot and root lengths, shoot and root biomass, K⁺ concentrations, and the K⁺/Na⁺ ratio in shoot dry matter decreased, while Na⁺ and Cl⁻ concentrations in shoot dry matter increased with rising salinity levels. STI values at 9.0 dS m⁻¹ indicated that two genotypes (S-5932 and S-5881) were tolerant, while four were moderately tolerant based on seedling emergence. Additionally, one genotype (S-5981) was tolerant, and six (S-5612, S-5881, S-5932, S-6003, S-6052, and S-6067) were moderately tolerant, based on the composite biomass of shoot and root. The seedling emergence, growth, and dry biomass reduction with increasing salinity underscore the importance of our research in identifying guar genotypes that can thrive in regions with salinity issues.