Águas salinas e aplicação foliar de peróxido de hidrogênio no cultivo de maracujazeiro amarelo.

Abstract

The passion fruit culture has great socioeconomic importance for the semi-arid region of the Brazilian Northeast. However, in this region, the salinity of water and soil has affected the agricultural production of crops. Thus, there is a need to search for alternatives that attenuate the effects of saline stress on agricultural crops, among them, yellow passion fruit. The objective of this study was to evaluate the growth, physiological indexes, production and post-harvest quality of yellow passion fruit cultivated under different levels of irrigation water salinity and exogenous application of hydrogen peroxide. The research was conducted in a greenhouse of the CTRN / UFCG, using the experimental design a randomized complete block design in a 4 x 4 factorial scheme with three replications. The treatments consisted of the combination of four levels of electrical conductivity of the water (0.7, 1.4, 2.1 and 2.8 dS m-1) and four concentrations of hydrogen peroxide (0, 20, 40 and 60 μM). Gaseous exchanges: CO2 internal concentration, CO2 assimilation rate, transpiration, stomatal conductance, water use efficiency, instantaneous carboxylation efficiency and intrinsic water use efficiency were evaluated at 61 and 96 days after transplanting (DAT). The passion fruit growth was determined by stem diameter at 35, 73 and 105 DAT; number of leaves at 35 and 73 DAT and absolute and relative growth rates of stem diameter in the periods of 8-35; 8-73 and 8-105 DAT and after the end of the cycle, dry leaf biomass (FSF), stem (FSC) and total (FST) were measured. At 186 DAT, the fluorescence of chlorophyll a was analyzed (initial fluorescence, maximum fluorescence, variable fluorescence and quantum efficiency of photosystem II) and the photosynthetic pigments: chlorophyll a (Cl a), b (Cl b) and carotenoids (Car ). At the end of the cycle (approximately 205 DAT), the production was evaluated, determining: number of fruits per plant, average fruit weight and total fruit weight per plant. The physical characterization of the fruits was also evaluated, determining the external attributes (equatorial and longitudinal diameter and the thickness of the peel and pulp) and internal attributes (pulp pH, titratable acidity (TA) and vitamin C). The increase in the salinity of the irrigation water caused a reduction in the gas exchange of yellow passion fruit at 61 and 96 DAT, being the rate of assimilation of CO2, perspiration, stomatal conductance and intrinsic efficiency of carboxylation affected, and also reduced the diameter of the stem at 35 , 73 and 105 DAT and the absolute growth rate of stem diameter in the period from 8 to 105 DAT. The increase in the concentrations of hydrogen peroxide had no influence on the gas exchange and the growth of yellow passion fruit. There was a significant interaction between irrigation water salinity and hydrogen peroxide concentrations on leaves at 35 DAT. Irrigation with CEa water from 1.4 dS m-1 compromised photochemical efficiency, photosynthetic pigments and phytomass production of yellow passion fruit. The application of hydrogen peroxide in the concentration of 20 μM promoted the highest values for variable and maximum fluorescence and carotenoid content constituting as an alternative for acclimatization of passion fruit. The supply of H2O2 in a concentration greater than 20 μM intensified saline stress on passion fruit. The increase in salinity levels of irrigation water affected negatively the production and physical and chemical quality of yellow passion fruit, being the number of fruits and the total weight of fruits per plant, the variables most affected to 205 DAT. There is a significant interaction between irrigation water salinity levels and hydrogen peroxide concentrations over the variable polar diameter of the fruit, at 205 days after transplanting. The foliar application of hydrogen peroxide at the concentrations of 27.5 and 41.5 μM, gives the highest titratable total acidity and vitamin C, respectively, at 205 DAT.