ABSTRACT
Aim: This study aims at exploring the interactive effect of salinity, a known inhibitor of plant growth,and salicylic acid (SA), a growth promoter, on niger [Guizotia abyssinica (L.f.) Cass], an oilseed crop plant, by assessing its growth, metabolism and defence system. Methodology: In a pot experiment, 4-week-old seedlings of niger were treated with NaCl (50, 100 and 150 mM added to the soil) and SA (1 mM aqueous solution sprayed on foliage) and watered regularly with 100% field capacity. A total of 8 treatments, including the control, were maintained for 8 weeks. Nine-week-old seedlings were sampled to analyze the growth attributes, plant water status, photosynthetic traits, lipid-peroxidation level, and activity of antioxidant enzymes. Results: Salinity treatments inhibited plant growth significantly, as evident from a dose-dependent reduction in size and biomass of roots and shoots. The reduction in stem basal diameter was significant only with 150 mM NaCl, a dose which also induced oxidative stress and enhanced lipid peroxidation. Salinity also reduced photosynthetic efficiency by inhibiting chlorophyll synthesis, nitrate reductase activity, chlorophyll fluorescence, stomatal conductance, net photosynthetic and transpiration rates, and plant water status. Reduction in relative water content was significant only at 150 mM of NaCl. High salinity also increased proline production and activity of antioxidant enzymes. Application of SA alone usually caused positive but non-significant effects on photosynthesis and growth parameters. SA application in combination with salt stress mitigated the salinity-induced adverse effects on growth and photosynthetic attributes. Moreover, upregulation of antioxidant enzymes evoked by salinity was further enhanced. Interpretation: Salinity hampered the overall performance of the crop, but SA application fortified its salt-tolerance capacity by alleviating the membrane injury and improving the assimilatory activities, plant water status and defense arsenal, thus reducing the adverse effects of salt stress on foliar functions and plant growth.