Physiological indices and growth of ‘Gigante Amarelo’ passion fruit under salt stress and silicate fertilization

Abstract

Abiotic stresses are responsible for the loss of agricultural production in different regions, especially in semiarid regions, which have long periods of drought and high evapotranspiration, leading to the use of saline water as an alternative for the expansion of irrigated areas. In this context, the objective was to evaluate the physiological indices and the growth of the ‘Gigante Amarelo’ passion fruit as a function of the salinity of irrigation water and fertilization with silicon. A randomized block design was used in a 5 x 2 factorial scheme, whose treatments consisted of five electrical conductivities of irrigation water - ECw (0.3; 1.0; 1.7, 2.4 and 3.1 dS m-1) associated with two doses of silicion (150 and 300 g of silicon plant-1) with four repetitions. Salt stress causes changes in gas exchange, chlorophyll a and b synthesis and growth of ‘Gigante Amarelo’ passion fruit plants, 60 days after transplanting. Fertilization with silicon dose of 300 g plant-1 promotes increments in CO2 assimilation rate and instantaneous water use efficiency, being able to mitigate the deleterious effects of salinity. Passion fruit plants fertilized with silicon dose of 300 g plant-1 attained greater growth in stem diameter and relative growth rate in stem diameter, from 30 to 60 days after transplanting.

Tolerance of sour passion fruit cultivars to salt stress in a semi-arid region

“…The reduction in the number of fruits of sour passion fruit plants may be related to the diversion of energy for maintaining metabolic activities, consequently causing a reduction in plant growth and production (Pinheiro et al, 2022). This situation reflects the action of osmotic effects, interfering with the absorption of water and nutrients by plants (Diniz et al, 2020). Reduction in the production of sour passion fruit due to salt stress was also observed by Nunes et al (2023), who found that the increase in ECw from 0.35 to 4.0 dS m -1 resulted in an 11.80% (13.25 fruits) decrease in the number of fruits per plant.…”

“…For the BRS GA1 cultivar, the RWC data (Figure 2A) was not satisfactorily described for prognostic purposes (R 2 <0,60) by the tested models (y = 82.882 -4.2113 ** x R² = 0.56). The presence of salts in the root zone triggers osmotic stress, which causes restrictions on the absorption of water and nutrients by plants (Diniz et al, 2020). According to Shahid et al (2020), high concentrations of salts make it difficult for plants to absorb water from the soil, reducing water conductivity of the root and consequently the relative water content at the cellular level.…”

“…Reduction in plant transpiration reflects the partial closure of the stomata and occurs due to the osmotic effects, which inhibit the absorption of water by plants, limiting the flow of water vapor into the atmosphere (Dias et al, 2019). Diniz et al (2020), in a study with yellow passion fruit seedlings under irrigation water salinity (between ECw 0.3 and 3.1 dS m -1 ), found a linear reduction in leaf transpiration, with decreases of 13.35% per unit increment in ECw. In the present study, plants subjected to ECw of 3.5 dS m -1 obtained an average value of 2.32 mmol H 2 O m -2 s -1 , being 0.610 mmol H 2 O m -2 s -1 higher than that observed in plants grown under water salinity of 3.1 dS m -1 from the study conducted by Diniz et al (2020).…”

“…When comparing the assimilation rate of plants irrigated with water of 3.5 dS m -1 to that of plants that received water of 0.3 dS m -1 , a decrease of 56.33% was observed. The reduction in the photosynthesis rate of sour passion fruit plants under salt stress conditions is related to the action of stomatal and non-stomatal factors, such as the restriction of CO 2 diffusion in the mesophyll cells and a decrease in the affinity of ribulose-1,5-biphosphate carboxylase-oxygenase (RuBisCO) with CO 2 (Soares et al, 2023), including changes in chlorophyll and carotenoid concentrations (Dias et al, 2019;Diniz et al, 2020). Silva et al (2019), when evaluating the gas exchange of passion fruit as a function of irrigation with saline waters (ECw ranging from 0.7 to 2.8 dS m -1 ), observed that the lowest CO 2 assimilation rate (8.18 μmol CO 2 m -2 s -1 ) was obtained in plants irrigated with water of 2.8 dS m -1 .…”