Exogenous application of phytohormones mitigates the effect of salt stress on Carica papaya plants

Aplicação exógena de fitormônios mitiga o efeito do estresse salino em plantas de Carica papaya

ABSTRACT

The salinity has complex effects on the physiological, nutritional and hormonal interactions of plants. This study aimed to evaluate the mitigating action of exogenous application of different types and concentrations of phytohormones on Carica papaya under salt stress. The experiment was conducted in greenhouse, using a randomized block design with treatments formed from a 2 x 3 x 5 factorial scheme, relative to two concentrations of salts in the irrigation water (0.6 and 2.4 dS m^-1), three types of phytohormones [Auxin = indole-3-acetic acid; Cytokinin = CPPU (N-(2-chloro-pyridyl)-N-phenylurea) and Gibberellin = gibberellic acid(AG₃)], and five concentrations of the phytohormone (0, 12.5, 25.0, 37.5 and 50.0 µM L^-1), with three repetitions, totaling 90 plots, and the experimental unit consisted of six plants. C. papaya cv. ‘Sunrise Solo’ was grown on polyethylene trays of 162 cells, with capacity for 50 mL. The plants were evaluated for survival percentage and phytomass accumulation until 25 days after sowing. Increase in irrigation water salinity has deleterious effects on C. papaya plants regardless of the application of phytohormones. Exogenous application of gibberellin has a positive effect in mitigating salt stress on C. papaya plants, greater than the effects of auxins and cytokinins. Exogenous application of gibberellin and auxin at concentration of 37.5 µM L^-1 mitigates the effects of salinity on C. papaya plants. Exogenous application of cytokinin at concentrations of 12.5 to 50.0 µM L^-1 is not viable for C. papaya plants.

Key words:
auxins; cytokinins; gibberellins; salinity