Abstract:
Keeping in view the emerging role of a recently discovered phytohormone, strigolactones (GR24), experiments were carried-out to explore whether GR24 could alleviate the nastiest impact of salinity on spring sunflower (Helianthus annuus L.). Two experiments, the first as pre-sowing and second as foliar spray were held during the months of February to May, in the year 2015 and 2016 in the Botanical Garden of the University of Agricuture, Faisalabad. In the first experiment, achenes of sunflower hybrids (FH-593 and FH-596) were primed in GR24 solutions i.e. 0, 0.001, 0.01, 0.1 mg L-1 for 16 hours. Two salt stress levels, 0 mM (Control) and 120 mM NaCl was applied to twenty four days old plants. Salt stress considerably reduced growth, leaf water relations, pigments, gas exchange attributes, mineral nutrients and yield parameters. GR24 treated achenes showed improvement in growth, water use efficiency and yield attributes except 100 achene weight and achene number per plant. Salt stress augmented the secondary metabolites, antioxidants and compatible solutes for defensive purpose, ROS and sodium accretion as stress marker. Pre-achene treatment with GR24 further accumulated carotenoid, antioxidants, organic osmolytes, anthocyanin, hydrogen peroxide, and shoot potassium and calcium in both hybrids of sunflower under non-saline and saline environment. During second experiment, 36 days old plants of sunflower were sprayed with GR24 (0, 0.001, 0.01, 0.1 mg L-1). Salt stress reduced growth attributes, gas exchange parameters and photosynthetic pigments significantly. GR24 enhanced growth and gas exchange attributes except stomatal conductance and net CO2 assimilation rate, activities of non-enzymatic as well as enzymatic antioxidants, secondary metabolites and osmolytes, GR24 foliar application enhanced glutathione reductase and peroxidase, ascorbic acid, soluble phenolics, organic osmolytes, ROS, secondary metabolites, free proline, total soluble sugars, glycinebetaine, saponin, tannin, free amino acids. GR24 treatment as foliar application only enhanced shoot potassium and calcium. GR24 spray accelerated achene yield and head diameter only. Sunflower hybrid FH-596 performance was better than FH-593.
