The effect of exogenous glycine betaine on yield of soybean [Glycine max (L.) Merr.] in two contrasting cultivars Pershing and DPX under soil salinity stress

Salinity stress restricts growth of soybean plant [Glycine max (L.) Merr.]. Glycine betaine (GB) is among osmoprotectant compounds that are produced in tolerant plant species in response to environmental stresses. Soybean is sensitive to soil salinity and is classified as a low-ccumulator of glycine betaine. Therefore, this study was performed to evaluate the salinity tolerance of two contrasting soybean [Glycine max (L.) Merr.] cvs. Pershing and DPX at field saline soils (EC=11.1 dS/m-1). The exogenous glycine betaine (Exo-GB) treatments (0, 2.5, 5, 7.5 and 10 kg/ha) were applied in six foliar and near the flowering stages. During the growth period the amount of endogenous-glycine betaine (Endo-GB) was measured in ten foliar stages and in leaves of seeding stage. Results showed that the uptake of Na+ decreased in response to increment of Exo-GB levels, in which tolerant cv. DPX (24%) had a greater capacity to prevent Na+ uptake. Endo-GB had higher concentrations in younger leaves than in mature leaves. Exo-GB increased the number of lateral branches significantly (33%) and especially pods per plants (49%) in cv. DPX. There was no difference in seed number per pod between controls and all levels of Exo-GB treatments in two cultivars. All treatments of Exo-GB significantly increased weight of thousands grain (highest; 71% in 10 kg ha-1 GB) in salt tolerant cv. DPX. Application of Exo-GB on weight of thousands grain was cultivar-, dose-, and time-dependent. The grain yield of soybean was increased by foliar applications of Exo-GB. This was due to significant increase in number of lateral branches and pods and weight of thousands grain, without significant different between cultivars.