Use of Proline to Induce Salt Stress Tolerance in Guava.

Guava is a fruit tree with high potential in the semi-arid region of northeast Brazil. However, qualitative and quantitative water scarcity is a limiting factor for the expansion of irrigated agriculture. Thus, it is necessary to use techniques to mitigate the effects of salt stress, such as foliar application of proline. The objective of this study was to evaluate the effect of foliar application of proline as a mitigator of salt stress effects on the morphophysiology of guava cv. Paluma. The experiment was carried out under field conditions at the 'Rolando Enrique Rivas Castellón' Experimental Farm in São Domingos, PB, Brazil, using a randomized block design in a 5 × 4 factorial scheme referring to five levels of electrical conductivity of irrigation water, ECw (0.8, 1.5, 2.2, 2.9, and 3.5 dS m-1) and four concentrations of proline (0, 8, 16, and 24 mM). Salinity above 0.8 dS m-1 compromised gas exchange, photosynthetic pigment synthesis, photochemical efficiency, and growth of guava plants at 360 days after transplanting. Foliar application of proline at a concentration of 24 mM mitigated the effect of salt stress on the relative water content, stomatal conductance, and carotenoid contents in plants irrigated with 3.6 dS m-1 water. Meanwhile, a proline concentration of up to 18 mM resulted in higher transpiration, CO2 assimilation rate, instantaneous carboxylation efficiency, and absolute growth rate in stem diameter under ECw of 0.8 dS m-1. Proline concentration of up to 24 mM increased the biosynthesis of photosynthetic pigments and the relative growth rate in stem diameter of guava in the period from 190 to 360 days after transplanting.

Hydrogen Peroxide Alleviates Salt Stress Effects on Gas Exchange, Growth, and Production of Naturally Colored Cotton.

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 Effects of Irrigation Water Salinity on the Synthesis of Photosynthetic Pigments, Gas Exchange, and Photochemical Efficiency of Sour Passion Fruit Genotypes.

The objective of this study was to evaluate the synthesis of photosynthetic pigments, gas exchange, and photochemical efficiency of sour passion fruit genotypes irrigated with saline water under the conditions of the semi-arid region of Paraíba state, Brazil. The experiment was conducted at the experimental farm in São Domingos, PB. A randomized block design was adopted, in a 5 × 3 factorial scheme, with five levels of electrical conductivity of irrigation water-ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1)-and three genotypes of sour passion fruit (Gigante Amarelo-'BRS GA1'; Sol do Cerrado-'BRS SC1'; and Catarina-'SCS 437'. The increase in the electrical conductivity of irrigation water negatively affected most of the physiological characteristics of the sour passion fruit at 154 days after transplanting. Significant differences were observed between sour passion fruit genotypes when its tolerance was subjected to the salinity of irrigation water. There was an increase in the percentage of damage to the cell membrane with the increase in the electrical conductivity of irrigation water, with maximum values of 70.63, 60.86, and 80.35% for the genotypes 'BRS GA1', 'BRS SC1', and SCS 437', respectively, when irrigated with water of 3.5 dS m-1. The genotype 'BRS Sol do Cerrado' showed an increase in the synthesis of photosynthetic pigments when irrigated with water of 3.5 dS m-1, with maximum values estimated at 1439.23 µg mL-1 (Chl a); 290.96 µg mL-1 (Chl b); 1730.19 µg mL-1 (Chl t); and 365.84 µg mL-1 (carotenoids). An increase in photosynthetic efficiency parameters (F0, Fm, and Fv) of the genotype 'BRS Gigante Amarelo' was observed when cultivated with water with high electrical conductivity (3.5 dS m-1).

NPK Accumulation, Physiology, and Production of Sour Passion Fruit under Salt Stress Irrigated with Brackish Water in the Phenological Stages and K Fertilization.

This research aimed to evaluate the effects of salt stress, varying the phenological stages, and K fertilization on NPK concentrations, physiology, and production of Passiflora edulis Sims. The research was carried out at the University Farm of São Domingos, Paraíba, Brazil, using a randomized block design with a 6 × 2 factorial arrangement. Six irrigation strategies were evaluated (use of low electrical conductivity water (0.3 dS m-1) during all stages of development and application of high-salinity water (4.0 dS m-1) in the following stages: vegetative, flowering, fruiting, successively in the vegetative/flowering, and vegetative/fruiting stages) and two potassium levels (207 and 345 g K2O per plant), with four replications and three plants per plot. The leaf concentrations of N, P, and K in the sour passion fruit plants found in the present study were below the optimal levels reported in the literature, regardless of the development stage and the cultivation cycle. The relative water content, stomatal conductance, and photosynthesis were reduced by salt stress in the first cycle. However, in the second cycle, irrigation with 4.0 dS m-1 in the vegetative/flowering stages increased the CO2 assimilation rate. Passion fruit is sensitive to salt stress in the vegetative/flowering stages of the first cycle. In the second cycle, salt stress in the fruiting stage resulted in higher production per plant.