Exogenous application of salicylic acid for regulation of sunflower growth under abiotic stress: a systematic review

In the current review, peer-reviewed publications from the Web of Science and SCOPUS databases concerning the impact of exogenous application of salicylic acid (SA) on sunflower growth in stressful environments were analyzed. Nine studies reported that SA application improved sunflower growth under salinity stress by enhancing K+ uptake and depressing Na+ and Cl− in the plant, increasing the activity of superoxide dismutase and peroxidase in the leaves, as well as raising chlorophyll a and b, leaf turgor, and Ca2+ concentrations in the leaves and root. Seven studies reported improvement of growth under drought by improving water relations, leaf free proline, leaf glycine betaine, and total soluble sugars. Five studies showed reduction of toxic metal stress through the promotion of endogenous SA anabolism (biosynthesis), higher enzymatic activity of catalase, ascorbate peroxidase, and glutathione peroxidase, coupled with lower activity of superoxide dismutase and guaiacol peroxidase, and accumulation of osmolytes that protect the photosynthetic pigments. Three studies showed protection of sunflower growth under chilling after seed conditioning, which decreased electrolyte leakage and stimulated dehydrogenases activity. One study found higher values of total chlorophyll, carotenoids, and water content under the effect of the herbicide fluorochloridone. Overall, SA could be used as a promising compound for increasing sunflower tolerance to abiotic stress, yet more information is required regarding the number of SA applications per growing season, the appropriate dosage, and the appropriate growth stage of sunflower for maximum yield benefit, along with the economic feasibility of the SA applications.