Response of salt stressed okra (Abelmoschus esculentus Moench) plants to foliar-applied glycine betaine and glycine betaine containing sugarbeet extract

The present experiment was aimed at examining the ameliorative effect of foliar-applied glycine betaine (50mM GB) and glycine betaine containing sugarbeet extract (50mM GB) on various physiological and biochemical attributes of okra plants under salt stress. The experiment comprised of two okra cultivars (Arka-anamika and Sabaz-pari), two salt levels (0 and 150mM NaCl), and two GB sources (synthetic pure GB and sugarbeet extract) arranged in four replicates. Salt stress significantly suppressed the biomass production, yield, and different gas exchange attributes (A, E, Cᵢ, and gₛ). Glycine betaine and proline contents in leaves, and Na⁺ and Cl⁻ contents in both leaves and roots increased, while K⁺ and Ca²⁺ contents and K⁺/Na⁺ ratios decreased significantly. Foliar application of both pure GB and sugarbeet extract significantly reduced the adverse effects of salt stress on plant biomass production, plant yield, various gas exchange characteristics and leaf K⁺, Ca²⁺, Cl⁻ and Na⁺ contents. However, GB and sugarbeet extract showed differential effects on A, gₛ, E, Cᵢ, Cᵢ/Ca ratio, leaf K⁺, Ca²⁺, and Cl⁻ contents, and K⁺/Na⁺ ratio. Pure GB proved better than the sugarbeet extract in improving growth, while the reverse was true for plant yield under salt stress. However, with respect to different gas exchange attributes both GB and sugarbeet extract were found to be equally effective in reducing the adverse effects of salt stress on these photosynthetic attributes. Foliar-applied sugarbeet extract was found to be more effective as compared to pure GB in reducing the adverse effects of salt stress on K⁺ and Ca²⁺ uptake and K⁺/Na⁺ ratio in shoot and root of both okra cultivars. Thus, sugarbeet extract could be used to induce salt tolerance in economically important crop plants.