Screening of Sweet Sorghum Genotypes for Salt Tolerance and Comparative Na+ Transporter Gene Expression in Salt Tolerance Differing Genotypes at Seedling Growth Stage

The present study was planned to screen the sweet sorghum genotypes at the sensitive seedling stage against salinity with specific morpho-physiological and biochemical attributes that could contribute to their adaptability to salinity stress. Therefore, 14 sweet sorghum genotypes were subjected to five different NaCl salt concentrations (0 mM (C), 50 mM, 100 mM, 150 mM and 200 mM), and 5 days after germination (DAG), the seedlings were evaluated for morpho-physiological parameters (percent germination, shoot and root lengths, seedling biomass and seedling vigor indexes I and II), total sugars, total chlorophyll and Na+/K+ ratio. Correlation, heat map and principle component analysis revealed that germination percentage is highly correlated with seedling vigor indexes (I and II) and seedling fresh weight. The sweet sorghum genotypes showed a significant reduction in morpho-physiological traits with a minimum effect seen in PHULE VASUNDHARA and SSV 84 with increasing salt stress. Two clusters were obtained on the basis of all studied traits: in cluster I, PHULE VASUNDHARA and SSV 84 with better seedling growth, biochemical parameters (total sugars and total chlorophyll) and higher K+ concentration were grouped together and in cluster II, 12 genotypes were clustered together. Further, gene expression analysis of ion transporters (HKT-6 and HAK) confirmed the observed lower Na+/K+ ratio due to more HKT-6 ion transporter gene expression in the roots of the selected tolerant PHULE VASUNDHARA as compared to the selected sensitive SPV 2074 with more expression of ion transporter HAK, suggesting that this Na+/K+ ratio could be a reliable trait for salinity tolerance screening at seedling growth stage. Further, tolerant genotypes could be a prominent resource for further use in salinity tolerance breeding of sweet sorghum.