Application of phytohormones as attenuators of salt stress in Tropaeolum majus L. (Tropaeolaceae)

The salinity of the soil and irrigation water is one of the great challenges of agriculture. Salinity can have harmful effects on physiological processes and plant growth, including Tropaeolum majus L. (Tropaeolaceae). The application of phytohormones can be a strategy to mitigate these effects. The aim of this study was to evaluate the application of jasmonic acid, salicylic acid, cytokinin and polyamine as attenuators of salt stress in T. majus . Three levels of salt stress were used: 0 mM NaCl (no stress), 50 mM NaCl (moderate stress) and 100 mM NaCl (severe stress). Four phytohormones and a control treatment were used: control (deionized water), jasmonic acid (200 µM), salicylic acid (2 mM), cytokinin (6-benzylaminopurine – 10 µM) and polyamine (spermine – 1 mM). Growth and gas exchange parameters were evaluated. Applied in conditions of moderate salt stress, all the phytohormones were efficient in improving plant height and leaf area (except salicylic acid); cytokinin and polyamine improved the number of flowers as well as gs, A and iCE; jasmonic acid improved the stem dry mass and total dry mass. In relation to severe salt stress, applications of jasmonic acid and polyamine were efficient in improving plant height; cytokinin improved leaf dry mass as well as gs, A, E, WUE, iWUE and iCE. The application of cytokinin, polyamine and jasmonic acid can be used to mitigate moderate salt stress in T. majus.