Moringa Leaf Extract (MLE) Seed Priming Provides Early Seedling Protection to Biofuel Crop: Sweet Sorghum—Against Salinity

Sorghum seed germination is delayed/inhibited by salt stress, and moringa leaf extract (MLE), a natural growth enhancer, acts as a low-cost seed priming agent which promotes the germination under stress condition. Therefore, during the current investigation two sweet sorghum genotypes (salt tolerant and salt susceptible) were exposed to 100 mM salt stress (NaCl) and data pertaining to seedling growth, enzymatic activities, ionic balance and gene expression were recorded at 10 days after germination (DAG) in shoot and root tissues. The seeds were primed with MLE extract (10% v/v) to mitigate the effects of salt stress. Results showed that salt stress inhibited the seedling growth of sweet sorghum. MLE priming positively enhanced the seedling growth by inducing production of total phenols, total sugars and improving the chlorophyll content with improved nitrogen metabolism under salt treatment. Under salt stress, MLE priming resulted in a significantly enhanced antioxidant enzyme activities (SOD, APX, CAT and PPO) and related gene expression, whereas it reduced the Na⁺ /K⁺ ratio, due to induced expression of the HKT-6 and HAK genes in roots. Overall, salt-tolerant sorghum genotype performed better than susceptible genotype under salt stress. The present investigation suggested that MLE priming provided an early seedling protection by improving germination, enzymatic activities and expression of nitrogen metabolizing and antioxidant genes under salt stress.