A pot experiment was carried out to investigate the effect of foliar spray with GA3 on growth and chemical composition of damsisa plants (Ambrosia maritima L) grown under saline conditions. Results revealed that increasing the concentration of salts reduced, plant height, number of leaves, number of branches, stem diameter, root length, as well as the fresh and dry weight of leaves and roots. Under saline conditions chlorophyll, a. b and total carotenoids, total carbohydrates, total indols, N, P and K were markedly reduced. However, total free amino acids, proline, total and reducing sugars, total and free phenols, Na and total sesquiterpene lactones content in leaves were increased. Treatment with GA3 at 100 ppm nullified the harmful effect of salinity and increased sail tolerance by increasing synthesis of different metabolites (sugars, free amino acids, proline and phenols) and enhancing biochemical and physiological processes and consequently increase the biosynthesis and accumulation of the major active constituent (sesquiterpene lactones) which have an insecticidal activity against bilharzias
