Alleviating salinity stress in Cyamopsis tetragonoloba L. seedlings through foliar application of silicon or melatonin in arid and semi-desert environments

Salinity stress can be deemed as an important challenge extremely affecting crop growth as well as development. Therefore, it is important to improve its tolerance to salinity stress, in arid as well as semiarid regions. Thus, this experiment explored the influence of foliar usage of plant growth-stimulating substances with different concentrations (C: control, melatonin (M1: 100, M2: 200 and M3:400 µM) and silicon (Si1: 5.4, Si2: 10.8 and Si3: 16.2 mM)) on some physiological as well as biochemical attributes of Cyamopsis tetragonoloba L. (guar) seedlings under five salinity levels (S1: no-salt treatment, S2: 5, S3: 10, S4: 15 and S5: 20 dS m−1). With increasing salinity, shoot dry weight, Fv/Fm, F′v/F′m, ΦPSII, qp, qL, Rfd, ETR, photosynthetic pigments, membrane stability index, as well as relative water content were gradually reduced in salt-stressed guar, as comparison is made to the non-saline conditions. However, foliar usage of plant growth-stimulating substances was effective in improving guar tolerance to salinity by elevating the DPPH radical scavenging capacity and anthocyanin, thus enhancing membrane stability index, improving the electron's transport rate, reducing electrolyte leakage and decreasing the damage affecting the reaction center of PSII, as comparison is made with control. Such positive effects were exhibited in elevating growth under salinity stress. Si3 treatment demonstrated the best response under salinity stress, as compared with the other treatments. Consequently, foliar usage of silicon or melatonin in salt-stressed guar seedlings can serve an efficient method to improve salt tolerance under salinity stress in arid and semiarid regions.