Glycinebetaine, an osmolyte of interest to improve water stress tolerance in sunflower (Helianthus annuus L.): water relations and yield

Two sunflower lines, namely, Gulshan-98 (dwarf) and Suncross (tall) were subjected to water stress environment at the vegetative or reproductive growth stage. Three levels (0, 50 and 100 mM) of glycinebetaine (GB) were applied before sowing (seed treatments) or at the start of water deficit treatments (foliar application) at the vegetative or reproductive growth stage. Water stress significantly decreased leaf water contents, osmotic and turgor potentials in both sunflower lines. Pre-treatment of seeds with both levels of GB did not affect above mentioned water relation parameters under both control (normal irrigation) and water stress environments. Foliar application of GB at the vegetative or reproductive growth stage, however, increased leaf water and turgor potentials to some extent in both sunflower lines when grown under water stress. The leaf osmotic potential was not affected by exogenous supply of GB at either growth stage. However, water stress induced decline in achene yield/plant was significantly reduced by the foliar application of GB. Foliar spray of 100 mM GB was found to be more beneficial in preventing the effects of water stress on above mentioned attributes as compared with 50 mM GB.