Gas exchange, photochemical efficiency and growth of hydroponic okra under salt stress and salicylic acid

ABSTRACT Okra (Abelmoschus esculentus L.) is a shrub belonging to the Malvaceae family, which stands out for its rusticity and adaptation to soil and climatic conditions, being cultivated by small farmers, especially in the semi-arid region of Northeast Brazil. In this context, the objective of this study was to evaluate the effect of foliar application of salicylic acid as an attenuator of salt stress on leaf gas exchange, photochemical efficiency, and growth of okra cv. Canindé in a hydroponic system. The experiment was carried out using a Nutrient Film Technique - NFT hydroponic system in a greenhouse, in Pombal, PB, Brazil, from January to March 2022, in a completely randomized design, in a split-plot scheme, with the four levels of electrical conductivity of the nutrient solution - ECns (3.0, 5.0, 7.0, and 9.0 dS m-1) considered as plots and four concentrations of salicylic acid – SA (0, 1.2, 2.4, and 3.6 mM) considered as subplots, with three replicates and two plants per plot. Increase in ECns levels from 3.0 dS m-1 inhibited leaf gas exchange, photochemical efficiency, and growth of okra cv. Canindé in hydroponic cultivation, at 34 days after transplanting. Foliar application of SA at concentrations of 2.2 and 1.5 mM promoted increments in stomatal conductance and transpiration, respectively. Salicylic acid at concentration of 1.9 mM associated with saline nutrient solution of 9.0 dS m-1 increased the variable fluorescence of okra plants cv. Canindé, at 34 days after transplantation. RESUMO O quiabeiro (Abelmoschus esculentus L.) é um arbusto que pertencente à família Malvaceae, que se destaca pela rusticidade e adaptação às condições edafoclimáticas, sendo cultivado por pequenos agricultores, especialmente no semiárido do Nordeste do Brasil. Neste contexto, objetivou-se com este estudo avaliar o efeito da aplicação foliar de ácido salicílico como atenuante do estresse salino nas trocas gasosas foliares, eficiência fotoquímica e crescimento de quiabeiro cv. Canindé em sistema hidropônico. O trabalho foi desenvolvido em sistema hidropônico tipo Técnica de Fluxo de Nutrientes - NFT em casa de vegetação, em Pombal – PB, durante o período de janeiro a março de 2022, utilizando-se o delineamento inteiramente casualizado, em esquema parcelas subdivididas, sendo os quatro níveis de condutividade elétrica da solução nutritiva - CEsn (3,0; 5,0; 7,0 e 9,0 dS m-1), considerados as parcelas e as quatro concentrações de ácido salicílico - AS (0; 1,2; 2,4 e 3,6