Biostimulant based on Ascophyllum nodosum in the formation of mint seedlings under salt stress

Abstract

Mint stands out for its flavoring and therapeutic properties. However, its cultivation in the semi-arid region is limited due to the salinity in the irrigation water. As an alternative, to alleviate the harmful effects of salt stress, seaweed-based biostimulants have been used. Thus, the objective was to evaluate the effect of a biostimulant based on Ascophyllum nodosum on the levels of photosynthetic pigments, photochemical efficiency and growth of mint under irrigation with saline water. The experiment was conducted in a greenhouse from, using a randomized block design, in an incomplete factorial scheme, with five levels of electrical conductivity of irrigation water – ECw (0.50, 1.23, 3.00, 4.77 and 5.50 dS m^-1) and five concentrations of seaweed-based biostimulant (0.00, 1.45, 5.00, 8.55 and 10.0 mL L^-1). The biostimulant at concentrations of 6.30 and 7.31 mL L^-1 alleviated salt stress effects on chlorophyll b content and Dickson quality index up to ECw of 3.41 and 2.71 dS m^-1. Foliar application of 10 mL L^-1 stimulated the formation of leaf and shoot biomass under ECw of 0.5 dS m^-1.              The increase in salinity did not compromise chlorophyll a and total chlorophyll contents, but reduced growth and biomass production. The highest quantum efficiency of photosystem II was obtained in plants subjected to ECw of 4.5 dS m^-1. Initial, variable and  maximum fluorescences were reduced with the increase in ECw from 0.5 dS m^-1. Foliar application of up to 10 mL L^-1 was efficient in reducing damage caused by salt stress in mint plants.