Abstract
Pecan [Carya illinoinensis (Wangenh.) K. Koch.] is a deciduous tree whose fruits (nuts) are of high economic value and offer excellent nutritional benefits. However, soils high in sulphates can limit its growth and development. Working with 5-year-old trees of ‘Western Schley’ pecan grown in soils high in sulphates, the levels of proline and oxidative metabolism were recorded in the leaflets. Results showed that different levels of visible leaflet damage (‘sufficiency’, ‘low’, ‘moderate’ or ‘severe’) were associated with different levels of leaflet sulphates (mg kg−1): ‘sufficiency’ (≤40), ‘low’ (41–60), ‘moderate’ (61–80) and ‘severe’ (80–100). ‘Severe’ sulphate damage was associated with significant reductions in chlorophyll (TChl) (17.04 μg g−1), relative water content (RWC) (50%) and leaf area (LA), and with increases in the concentrations of total carotenoids (TC) and proline (Prl). Increases were also observed in the activities of the oxidative metabolism enzymes: superoxide dismutase (SOD) (1.82 units min−1 g−1), catalase (CAT) (2.86 μmol H2O2 min−1 g−1) and antioxidant capacity (AC) (87% DPPH inhibition). However, guaiacol peroxidase (GP) showed a reduction (2.97 nmol GSH min−1 g−1). An inverse relationship was found between the sulphate concentration in the leaflets with respect to the evaluated parameters of TChl, TC, RWC, LA, AC, and GP. Proline synthesis and antioxidant enzymatic activity indicate salt stress in pecan leaflets in orchards irrigated with deep-well water high in sulphates.
Highlights
In many arid and semi-arid regions of the world, salinity stress limits agricultural and horticultural production
Previous studies have reported the negative effects of high concentrations of NaCl and Na2SO4 on the activity of RuBisCO, PEP and antioxidant capacity (AC) all of which impact the efficiency of photosynthesis in leaflets of pecan tree [27]
The lowest total chlorophyll values corresponded to leaflets from trees showing ‘moderate’ (23.66 μg g−1) to severe (17.04 μg g−1) salinity damage
Summary
In many arid and semi-arid regions of the world, salinity stress limits agricultural and horticultural production. Koch], this occurs especially where poorquality irrigation water contributes to the accumulations of various salts in the upper soil layers [1,2]. Excessive accumulations of Na+, Mg2+, Ca2+, Cl−, SO42− or HCO3−/CO32− are all associated with salt stress. In many areas of commercial pecan production, SO42− is the dominant salt at issue [3]. The pecan is one of the most sensitive to salt stress [1,2].
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