Cotton is one of the most exploited crops in the world, being one of the most important for the Brazilian Northeast. In this region, the use of irrigation is often necessary to meet the water demand of the crop. Water is often used from underground wells that have a large amount of salt in their constitution, which can compromise the development of crops, so it is vital to adopt strategies that reduce salt stress effects on plants, such as the foliar application of hydrogen peroxide. Thus, the objective of this study was to evaluate the effects of foliar application of hydrogen peroxide on the gas exchange, growth, and production of naturally colored cotton under salt stress in the semi-arid region of Paraíba, Brazil. The experiment was carried out in a randomized block design in a 5 × 5 factorial scheme, with five salinity levels of irrigation water—ECw (0.3, 2.0, 3.7, 5.4 and 7.1 dS m⁻¹)—and five concentrations of hydrogen peroxide—H₂O₂ (0, 25, 50, 75 and 100 μM), and with three replicates. The naturally colored cotton ‘BRS Jade’ had its gas exchange, growth, biomass production, and production reduced due to the effects of salt stress, but the plants were able to produce up to the ECw of 3.97 dS m⁻¹. Foliar application of hydrogen peroxide at the estimated concentrations of 56.25 and 37.5 μM reduced the effects of salt stress on the stomatal conductance and CO₂ assimilation rate of cotton plants under the estimated ECw levels of 0.73 and 1.58 dS m⁻¹, respectively. In turn, the concentration of 12.5 μM increased water-use efficiency in plants subjected to salinity of 2.43 dS m⁻¹. Absolute and relative growth rates in leaf area increased with foliar application of 100 μM of hydrogen peroxide under ECw of 0.73 and 0.3 dS m⁻¹, respectively. Under conditions of low water salinity (0.3 dS m⁻¹), foliar application of hydrogen peroxide stimulated the biomass formation and production components of cotton.

The occurrence of water with high concentrations of salts hinders the expansion of irrigated agriculture in the semi-arid region of the Brazilian Northeast, making it necessary to adopt strategies capable of minimizing the effects of salt stress on plants. In this context, the objective of present study was to evaluate the effects of hydrogen peroxide application on water relations, gas exchange, photosynthetic pigments, and growth of guava cv. Paluma under irrigation with saline waters in the seedling formation stage. A randomized block design was used, in a 5 × 4 factorial scheme, with three replicates, with five levels of electrical conductivity of water - ECw (0.3, 1.3, 2.3, 3.3, and 4.3 dS m^-1) and four concentrations of hydrogen peroxide - H₂O₂ (0, 25, 50, and 75 µM). Irrigation water salinity above 0.3 dS m^-1 increased electrolyte leakage in the leaf blade and reduced the relative water content, synthesis of photosynthetic pigments, gas exchange, and growth of seedlings of guava cv. Paluma, at 80 days after sowing. Foliar application of hydrogen peroxide at concentrations of up to 75 µM reduces the relative water content in the leaf blade of guava seedlings and did not mitigate the effects of salt stress on guava plants in the seedling formation stage.

Practices that mitigate the deleterious effects of water deficit are of great importance for agricultural production in the semi-arid region of Northeastern Brazil. The objective of this study was to evaluate the effect of foliar application of salicylic acid on mitigating water deficit in the morphophysiology and yield components of sour passion fruit during different phenological stages. Treatments were arranged in a randomized block design in a 6 × 2 factorial scheme, consisting of six irrigation strategies under water deficit, based on reference evapotranspiration (ETr) [irrigation with 100% ETr throughout the entire cultivation cycle—IS1; irrigation with 50% ETr during the vegetative stage—IS2; flowering—IS3; fruiting—IS4; vegetative/flowering—IS5; and vegetative/fruiting—IS6], combined with or without salicylic acid (SA) application (0 and 1 mM). The application of 1.0 mM salicylic acid alleviated the effects of water deficit during the flowering stage, improving gas exchange, photochemical efficiency, relative water content, growth, and yield of sour passion fruit. In addition, it contributed to reducing electrolyte leakage in the leaf blade. Therefore, foliar application of salicylic acid represents a promising strategy to maintain the integrity of the photosynthetic apparatus and the productive performance of sour passion fruit under water deficit conditions.

Ascorbic acid is a non-enzymatic antioxidant compound essential for plant defense under salt stress conditions. It can induce salt stress tolerance and enable the use of saline water in hydroponic cultivation with substrates. This study evaluated the effect of foliar application of ascorbic acid on the yield and postharvest quality of ‘Laranja’ cherry tomatoes grown in saline nutrient solutions under a substrate-based hydroponic system. The experiment was conducted in a greenhouse in Campina Grande, Paraíba, Brazil, in a randomized block design in a 5 × 5 factorial arrangement, corresponding to five levels of electrical conductivity of the saline nutrient solution—SNS (2.1—Control, 2.8, 3.5, 4.2, and 4.9 dS m⁻¹) and five concentrations of ascorbic acid—AA (0, 150, 300, 450, and 600 mg L⁻¹), with four replications. Salinity above 2.1 dS m⁻¹ reduced yield components and phenolic compound content. However, the saline nutrient solution of 4.9 dS m⁻¹ combined with 600 mg L⁻¹ foliar application of AA increased fruit firmness, soluble solids, and titratable acidity. Additionally, SNS of 4.9 dS m⁻¹ enhanced the levels of vitamin C, flavonoids, and anthocyanins. While AA improved postharvest quality of cherry tomatoes, it did not increase production under salt stress. Foliar application is thus a promising approach for enhancing fruit quality of cherry tomatoes grown in hydroponic systems using saline water, supporting sustainable production in semiarid regions.

No semiárido do Nordeste do Brasil devido a irregularidade de precipitações e elevadas taxas de precipitações é comum a ocorrência de fontes hídricas com níveis elevados de sais dissolvidos, destacando-se como um fator limitante para o cultivo de espécies sensíveis ao estresse salino. Neste contexto, objetivou-se com este estudo avaliar fontes de nitrogênio nos aspectos fisiológicos, crescimento e qualidade de mudas de maracujazeiro-azedo cultivadas sob irrigação com águas salinas. A pesquisa foi conduzida em casa de vegetação pertencente à Unidade Acadêmica de Engenharia Agrícola da UFCG, em Campina Grande – PB, utilizando-se o delineamento experimental de blocos casualizados, em esquema fatorial 4 × 4, sendo quatro níveis de condutividade elétrica da água de irrigação - CEa (0,4; 1,4; 2,4 e 3,4 dS m-1) e quatro fontes de nitrogênio – FN (ureia, nitrato de cálcio, sulfato de amônio e cloreto de amônio), com quatro repetições e duas plantas por parcela. A irrigação com CEa acima de 0,4 dS m-1 aumentou o extravasamento de eletrólitos e, reduziu a transpiração, a condutância estomática, a clorofila b, a fitomassa seca de caule e de folhas, e o índice de qualidade de Dickson das mudas, independente da fonte nitrogenada fornecida. A adubação com sulfato de amônio aumentou o conteúdo relativo de água, o número de folhas, a concentração interna de CO2, a taxa de assimilação de CO2, a eficiência instantânea de carboxilação, a eficiência instantânea no uso da água e a altura de plantas das mudas. O fornecimento de nitrato de cálcio aumentou a concentração interna de CO2, a fitomassa seca de folhas e total, e os pigmentos fotossintéticos das mudas de maracujazeiro-azedo. A adubação com ureia aumentou a área foliar das mudas sob salinidade da água de 0,4 dS m-1. Recomenda-se adubação com sulfato de amônio para o cultivo de maracujazeiro-azedo irrigado com água de 3,4 dS m-1 durante a fase de formação de mudas.