Salinity is one of the most devastating abiotic stresses that limit plant growth and yield, especially in arid and semi-arid regions. The objective of this study was to evaluate the effect of foliar application of salicylic acid in mitigating the effects of salt stress on okra cultivation in a hydroponic system. The study was conducted in a greenhouse, consisting of two experiments. A completely randomized design was adopted in a split-plot scheme, with four levels of electrical conductivity of the nutrient solution—EC (2.1; 3.6; 5.1, and 6.6 dS m⁻¹) considered the plots and four salicylic acid concentrations—SA (0, 1.2; 2.4, and 3.6 mM), the subplots, with four replications. The second experiment differed from the first only by the increase in the EC levels (3.0, 5.0, 7.0, and 9.0 dS m⁻¹). An increase in the electrical conductivity of the nutrient solution negatively affected the physiology and production components of okra. However, foliar application of salicylic acid at concentrations between 1.2 and 2.3 mM reduced the harmful effects of salt stress. The salinity threshold for hydroponic cultivation of okra was 2.54 dS m⁻¹, with a reduction of 7.98% per unit increment in EC above this level.

Given the quantitative scarcity of low-salinity water resources in the Brazilian semi-arid region, it is necessary to use water with a high concentration of salts. Thus, identifying salt-stress tolerant cultivars of crops is an alternative for expanding irrigated agriculture. The objective of this study was to evaluate the tolerance of passion fruit cultivars as a function of irrigation water electrical conductivity. The experimental design was randomized blocks, in a 5 × 3 factorial scheme, whose treatments consisted of the combination of five values of electrical conductivity of irrigation water - ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m^-1) and three sour passion fruit cultivars (BRS GA1, BRS SC1, and SCS437, with three replicates. Electrical conductivity of water from 0.3 dS m^-1 reduces the relative water content, gas exchange, and the number of fruits and increased electrolyte leakage in the leaf blade of passion fruit plants, at 153 days after transplantation. The passion fruit cultivars BRS GA1, BRS SC1, and SCS437 were classified as sensitive, with threshold electrical conductivity of water of 0.3, 1.0, and 0.3 dS m^-1, respectively.

The excess of salts present in the water can limit the hydroponic cultivation of melon in semi-arid regions of the Brazilian Northeast, making it necessary to use strategies that allow the use of these waters. Among these strategies, the use of elicitor substances stands out, such as salicylic acid. In this context, this study aimed to evaluate the effect of foliar application of salicylic acid in mitigating the harmful effects of salt stress on the morphophysiology and production of 'Gaúcho' melon cultivated in a hydroponic system. A completely randomized design was adopted in a split-plot scheme, with four levels of electrical conductivity of the nutrient solution - ECsn (2.1, 3.2, 4.3, and 5.4 dS m-1) considered the plots and four salicylic acid concentrations - SA (0, 1.5, 3.0, and 4.5 mM), the subplots, with six replications. The foliar application of salicylic acid concentrations did not mitigate the deleterious effects of salt stress on the morphophysiology and yield of melon grown in hydroponic system. The concentration of 4.5 mM of salicylic acid intensified the harmful effects of the salinity of the nutrient solution on gas exchange and fresh weight of hydroponic melon.

A goiabeira é uma cultura importante no cenário socioeconômico da região semiárida brasileira, sendo uma fonte de geração de emprego e renda. Contudo, nesta região é comum a ocorrência de fontes hídricas com altos teores de sais dissolvidos e assim são necessárias estratégias que visem minimizar os efeitos deletérios do estresse salino nas plantas. Neste contexto, objetivou-se com este trabalho avaliar os efeitos da aplicação foliar com peróxido de hidrogênio nas trocas gasosas, eficiência fotoquímica, crescimento e qualidade de mudas de goiabeira sob estresse salino. O experimento foi conduzido sob condições de casa de vegetação em Pombal, Paraíba, utilizando-se o delineamento de blocos casualizados, com tratamentos arranjados em esquema fatorial 5 × 4 , referentes a cinco níveis de condutividade elétrica da água - CEa (0,3; 1,3; 2,3; 3,3 e 4,3 dS m-1) e quatro concentrações de peróxido de hidrogênio – H2O2 (0, 25, 50 e 75 μM) com quatro repetições e duas plantas por parcela. A irrigação com água de condutividade elétrica a partir de 0,3 dS m-1 inibiu as trocas gasosas, eficiência fotoquímica e crescimento de mudas de goiabeira, aos 91 dias após a emergência. A aplicação foliar de peróxido de hidrogênio em concentrações de até 75 μM não amenizou os efeitos do estresse salino em plantas de goiabeira na fase de formação de mudas. A goiabeira cv. Paluma é classificada como sensível a salinidade da água na fase de formação de mudas, sendo o nível limiar de 0,3 dS m-1 e diminuição por aumento unitário de 11,48%.

The objective of this study was to evaluate the physiology and growth of guava cv. Paluma as a function of irrigation with saline water and foliar application of ascorbic acid. The study was conducted using a randomized block experimental design in a 5 × 4 factorial scheme, whose treatments were formed by combining five levels of electrical conductivity of irrigation water - ECw (0.3, 1.2, 1.9, 2.6, and 3.3 dS m^-1), associated with four concentrations of ascorbic acid - AsA (0, 30, 60, and 90 mM), with three replicates and one plant per plot. Stem diameter, crown volume, vegetative vigor index, photosynthetic pigment contents, photochemical efficiency, electrolyte leakage, and relative water content were evaluated. Ascorbic acid at concentration of 60 mM increased electrolyte leakage and relative water content in plants under ECw of 3.2 and 2.9 dS m^-1, respectively. AsA concentration of 90 mM stimulated the biosynthesis of chlorophyll a, chlorophyll b, and total chlorophyll of guava plants grown under water salinity of 3.3 dS m^-1. Salinity above 0.3 dS m^-1 reduced chlorophyll a fluorescence, crown volume, and vegetative vigor index of guava. Foliar application of 30 mM ascorbic acid increased the quantum efficiency of photosystem II up to ECw of 2.5 dS m^-1. The beneficial effect of ascorbic acid was obtained under ECw of 0.3 dS m^-1.

In order to study the effect of salicylic acid concentrations on the mitigation of salt stress in melon plants grown on a hydroponic system an experiment was conducted in a greenhouse at Pombal – PB, Brazil, using an NFT (Nutrient Film Technique) system. The experimental design was completely randomized, in a 4 × 4 factorial scheme, corresponding to four levels of electrical conductivity of the nutrient solution—ECns (2.1—control, 3.2, 4.3, and 5.4 dS m⁻¹) and four concentrations of salicylic acid—SA (0, 1.5, 3.0, and 4.5 mM), with six replicates. Salicylic acid at the concentration of 3.2 mM attenuated the effect of nutrient solution salinity on the fresh weight of melon fruits. The saline nutrient solution impairs gas exchange and the relative water content and increases the intercellular electrolyte leakage in the leaf blade of melon plants. However, salicylic acid attenuates the deleterious effects of salinity and attains a maximum yield of melon fruits of 23.82 t ha⁻¹ with foliar application of 1.5 mM at ECns of 3.1 dS m⁻¹. Salicylic acid stimulated the synthesis of total chlorophyll, the CO₂ assimilation rate, and the instantaneous water use efficiency of hydroponic melon up to a concentration of 4.5 mM. The results obtained indicate that the responses of the hydroponic melon plant grown with saline nutrient solution and the application of salicylic acid are not yet fully elucidated.