The supply of chemical fertilisers to complement the soil’s natural fertility is essential in modern agriculture, which is struggling to satisfy the nutritional demands of the world. However, indiscriminate use and/or overuse of fertilisers has also increased agriculture’s adverse impacts on ecosystems and environmental quality (Cruz-Crespo et al., 2014; Mazaheri-Tirani et al., 2019). The performance of a chemical fertiliser can be reduced by several factors, including the soil characteristics (water content, pH, texture and structure), the fertiliser’s solubility and the dose applied (Zulfiqar et al., 2019). Zn is a micronutrient that plays important roles in the activities of oxidoreductases, lyases, isomerases, transferases, hydrolases and ligases (Singh et al., 2018). It is involved in various metabolic processes (photosynthesis; protein and carbohydrate metabolism) and is an integral part of the cell membrane (Küçükyumuk et al., 2014; Nandal and Solanki, 2021). In addition, Zn promotes the synthesis of tryptophan and auxins and plays a role in pollen development and fruit set (Xing et al., 2016; Santis et al., 2019). Because of its low mobility in the soil and plant, foliar supply of Zn is more efficient and also has less environmental impact (Fernández and Brown, 2013).
Among the fruit trees of temperate zones, the pecan tree [
The chelates are stable molecules that, when sprayed at high concentration, present reduced symptoms of phytotoxicity and can also be combined with humic and carboxylic acids (Doolette et al., 2018). Our earlier studies on foliar Zn applications to ‘Western Schley’ pecan trees using ZnNO3, zinc ethylene diamine-tetraacetic acid (Zn-EDTA) or Zn-diethylene triamine-pentaacetic acid (DTPA) (100 mg · L−1) showed significant variations in Zn uptake but without affecting nut yield or quality (Ojeda-Barrios et al., 2009, 2014). Similar results have been reported for the photosynthetic rate in terminal shoots of ‘Wichita’ pecans with the application of 3.75 mL · L−1 urea–ammonium nitrate (UAN), 3.6 g · L−1 ZnSO4, 3.6 g · L−1 ZnSO4 with 3.75 mL · L−1 UAN, 11 mL · L−1 Zn-EDTA (Smith et al., 2021). On the other hand, in other cultivars such as ‘Western Schley’, Naira et al. (2013) report improvements in leaflet growth after applying ZnSO4 (0.5%). Foliar fertilisation is often used to refer to the more general application of mineral nutrients, phytohormones, biostimulants and pesticides to the aerial parts of a plant.
In recent years, a wide range of problems in diverse fields of science and industry have been aided by nanotechnology. Nanomaterials are classified as material particles smaller in size than 100 nm in at least one dimension (Davarpanah et al., 2016). Metal and metal oxide nanoparticles (such as Cu, Ag, Mn, Mo, Zn, Fe, Si and Ti) exhibit different physicochemical characteristics from larger particles and so can be used for the design of new fertilisers with similar or better results compared with their native macro-particulate compounds (Nagula and Ramanjaneyulu, 2020). Compared with conventional fertilisers, nanoparticles (NPs) stand out for their higher specific surface-area ratios, surface-volume ratios and controlled release kinetics (Subbaiah et al., 2016; Zulfiqar et al., 2019). These properties allow much improved uptake efficiencies, so they can be supplied at low concentration but with similar or even better results than those obtained with the doses used in soil-surface fertilisation (Rossi et al., 2019). Thus, the NPs of ZnO have these characteristics, improving its solubility, diffusion rate and availability to the plant.
Till now, research on the effects of ZnO NPs relate mostly to non-woody plants, including peanut (
The research was carried out during the 2019 and 2020 production cycles on young (7-year-old) pecan [
Four different treatments were applied in a completely randomised design with 10 replications per treatment (40 trees in total). Each tree was one experimental unit. Tree height was 9.0 ± 0.5 m, and trunk girth was 55 ± 10 cm. All the spray solutions used contained 200 mg o L−1 Zn (3.06 mM) and included the proprietary product NZN [nitrazinc, containing Zn(NO3)2 and UAN fertiliser (Smith and Storey, 1979); Tessenderlo K, Inc., Phoenix, AZ, USA]; ZnSO4 (ZnSO4·7H2O reagent grade); Zn-EDTA (sodium salts and reagent grade ZnSO4·7H2O were added to make Zn(II)-EDTA); and ZnO NPs. The ZnO was obtained using wet chemistry as wurtzite crystals, of average size 50 nm with no contaminants (purity: 99.7%) and density 5.61 g · cm-3 (Figures 1 and 2). In all formulations, 0.1% urea was added as the carrier ion and 100 mg · L−1 of Tween
Approximately 50 pairs of leaflets were collected from each tree, from the middle of the canopy, on 20 July (2019 and 2020). This timing was during the growing season and was approximately 215 days after budding, in the water stage of the nut. Leaflets were collected by pooling samples from the four cardinal directions (north, south, east and west) and from both vegetative and fruiting shoots. Collected materials were without obvious mechanical damage, pests or diseases. Nut collection was carried out in the last week of November by mechanical vibration of the trees.
Extraction and quantification of glucose, fructose, sucrose and starch were carried out according to the method described by Ojeda-Barrios et al. (2022).
Briefly, a sample of 1 g of fresh tissue was taken and homogenised twice, first with 5 mL of 95% aqueous ethanol (v:v) and next with 70% aqueous ethanol (v:v). The mixture was centrifuged at 5,500
The performance components were determined according to Mexican Standard NMX-FF-084-SCFI-2009. The weight of the harvested nuts (fruits) was obtained using a Combo-Rhino-122 balance (Rhino
The leaflets were transported for analysis to the Plant Physiology Laboratory at Universidad Autonoma of Chihuahua, Mexico. Extraction and quantification of nutrients were carried out using the method published by Cruz-Álvarez et al. (2020). Briefly, a triple wash was carried out in tap water, then in 4 N HCl and finally in deionised water. Surface moisture was completely removed from the leaflets at room temperature, and the leaflets were then dried in a Heratherm VCA 230
The extraction and quantification of the photosynthetic pigments were carried out according to the method described by Wellburn (1994). Briefly, the samples were placed in flasks with 100 mL of 80% (v:v) acetone. The absorbance values at 665, 653 and 470 nm were recorded using a Lambda 25
The total phenol (TP) content was determined using the Folin-Ciocalteu method (Waterman and Mole, 1994) with slight modifications. Briefly, 0.5 g of sample was taken and homogenised with 5 mL of 70% (v:v) absolute ethyl alcohol. Next, an aliquot (50 μL) of this solution was taken and mixed with 7.95 mL of distilled water and 500 μL of the Folin–Ciocalteu (2N) reagent, then shaken for 1 min with a digital vortex (Thermo Scientific
Superoxide dismutase (SOD; Enzyme Commission [EC] number: 1.15.1.1) activity was assayed by monitoring the inhibition of the photochemical reduction of nitroblue tetrazolium (NBT), according to the method described by Giannopolitis and Ries (1977) and modified by Sánchez et al. (2005). Enzyme activity is reported as units per minute per gram FW, where 1 unit of SOD activity corresponds to the amount of enzyme required to cause a 50% inhibition of NBT reduction as evaluated at 560 nm. The extraction and analysis of total H2O2 used a colourimetric method (Sánchez et al., 2000). The results are reported in micromoles of H2O2 per minute per gram FW (total peroxides). Last, the extraction and determination of enzymatic activity of the enzymes catalase and guaiacol peroxidase were determined by the method described by Sánchez et al. (2000). The results are expressed as moles of H2O2 per minute per gram FW and nanomoles glutathione (GSH) per minute per gram FW, respectively.
Antioxidant capacity (AC) was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH˙) method. Aqueous ethanol (80%) was used for sample preparation. The DPPH’ assay was carried out in accordance with the procedure followed by Brand-Williams et al. (1995). Briefly, 0.3 mL of extract and 5.7 mL of DPPH were mixed at a concentration of 0.0375 g · L−1. The mixture was kept in the dark for 30 min. The decrease in the quantity of DPPH radical was measured at 515 nm. The results are expressed as percentage inhibition of DPPH.
Prior to statistical analysis, the normal distribution of the data was confirmed by the Shapiro–Wilk test (
It is well known that carbohydrates are key molecules in plants since they are part of the plant structure (e.g. cellulose) and are also the primary source of metabolic energy (e.g. starch) (Ojeda-Barrios et al., 2022). Here, the leaflets sprayed with sulphates, chelates and zinc NPs presented only slight numerical differences in the concentrations of NSCs (fructose, glucose, sucrose and starch), so it was not possible to identify a significant effect on NSCs between the two growing seasons examined (Table 1). These results are important, considering the negative impact of alternate bearing (AB) on pecan nut yield and quality (Wood et al., 2003; Rohla et al., 2007). Pecan trees quite commonly present AB; while the intensity of AB can be linked to the concentration of carbohydrates, it can also involve elements of agronomic management, such as irrigation, fertilisation, pruning and crop load. Other more random factors, such as water stress, lack of winter cold, tree age and cultivar, can also be involved (Wood et al., 2003). In Mexico, the main cultivars in commercial production are ‘Western Schley’, ‘Wichita’ and, more recently, ‘Pawnee’. Previous studies carried out to evaluate the intensity of AB in young and adult pecan trees by Conner and Worley (2000) report intermediate values in ‘Wichita’ (0.51 and 0.67) and ‘Western Schley’ (0.65 and 0.68); however, in ‘Pawnee’, there are no reports of AB, so it can be inferred that this is a promising new cultivar for pecan production.
Concentration of NSCs in ‘Western Schley’ pecan tree leaflets sprayed with sulphates, chelates and zinc nanoparticles.
Treatments (200 mg · L−1) | NSCs (g · kg−1) | |||||||
---|---|---|---|---|---|---|---|---|
Fructose | Glucose | Sucrose | Starch | |||||
2019 | 2020 | 2019 | 2020 | 2019 | 2020 | 2019 | 2020 | |
NZN (control) | 37.9 a | 34.3 a | 41.9 a | 38.0 a | 41.9 a | 43.5 a | 38.8 a | 40.2 a |
ZnSO4 | 40.7 a | 38.5 a | 45.0 a | 42.6 a | 37.5 a | 36.7 a | 34.6 a | 34.5 a |
Zn-EDTA | 39.3 a | 40.3 a | 43.5 a | 44.6 a | 40.8 a | 39.4 a | 37.5 a | 36.6 a |
ZnO NPs | 39.5 a | 38.2 a | 43.6 a | 42.9 a | 36.7 a | 39.3 a | 35.7 a | 39.6 a |
Means in the same row followed by the same letter were not significantly different (Tukey’s test,
NSC, Non-structural carbohydrate; ZnO NPs, zinc oxide nanoparticles; NZN, nitrazinc, containing Zn(NO3)2 and urea-ammonium nitrate fertiliser; Zn-EDTA, zinc ethylene diamine-tetra-acetic acid; ZnSO4, zinc sulphate.
The dormancy processes (paradormancy, endodormancy and ecodormancy) in temperate fruit trees are linked to various governing influences, including the environment and the genotype (Pertille et al., 2021). Among the internal factors governing dormancy are the concentrations of carbohydrates in leaves and buds (Wood et al., 2003; Rohla et al., 2007). In this study, foliar applications of Zn (NZN, ZnSO4, Zn-EDTA and ZnO NPs) did not affect (
On the other hand, we did find variation (
Yield, nut weight and kernel percentage in ‘Western Schley’ pecan tree leaflets sprayed with sulphates, chelates and zinc nanoparticles.
Treatments (200 mg · L−1) | Nut quality | |||||
---|---|---|---|---|---|---|
Yield (kg per tree) | Nut weight (g · kg 1 FW) | Kernel (%) | ||||
2019 | 2020 | 2019 | 2020 | 2019 | 2020 | |
NZN (control) | 9.9 a | 15.6 b | 156.1 a | 166.1 b | 52.2 a | 53.0 a |
ZnSO4 | 9.1 a | 14.1 b | 153.4 a | 167.4 b | 60.4 a | 58.0 a |
Zn-EDTA | 8.7 a | 14.9 b | 152.5 a | 164.5 b | 54.3 a | 54.3 a |
ZnO NPs | 9.9 a | 14.5 b | 158.6 a | 166.6 b | 54.9 a | 54.5 a |
Means in the same column followed by the same letters were not significantly different (Tukey’s test,
ZnO NPs, zinc oxide nanoparticles; NZN, nitrazinc, containing Zn(NO3)2 and urea–ammonium nitrate fertiliser; Zn-EDTA, zinc ethylene diamine-tetra-acetic acid; ZnSO4, zinc sulphate.
The data generated with the Zn spray and the plants’ responses to the foliar nutrient application between growing seasons are shown in Table 3. Previous studies have shown the nutritional effects of N and Zn2+ on the establishment and commercial production of pecan nuts (Cruz-Álvarez et al., 2020; Smith et al., 2021). Nitrogen is an essential nutrient in the accumulation of biomass, including for the development of shoots and leaflets. Its major roles in trees include its association with chlorophyll biosynthesis and the production of sugars by photosynthesis (Moran-Duran et al., 2020). Similar foliar N concentrations are reported by Pond et al. (2006) when determining the levels of foliar nutrients in ‘Western Schley’ pecan from high-yield commercial orchards established in the USA (Arizona, New Mexico and Georgia) (25.5, 24.7 and 27.2 g · kg−1) and in Sonora (Mexico) (24.8 g · kg−1). The variations between the values are probably associated with the physicochemical properties of the soil and the agronomic managements between growing seasons. On the other hand, in our study, the Zn concentrations fluctuated between 35.81 mg · kg−1 and 48.46 mg · kg−1, wherein NZN and ZnSO4 showed the best results. These results can be considered within the sufficiency range (30–100 mg · kg−1), as reported by Walworth and Heerema (2019). In contrast, Pond et al. (2006) report a foliar Zn sufficiency concentration of 54.6 mg · kg−1; however, our trees did not show visible deficiency symptoms (internode shortening, chlorosis and interveinal necrosis).
Nutrient concentrations in ‘Western Schley’ pecan tree leaflets sprayed with sulphates, chelates and zinc nanoparticles.
Treatments (200 mg · L−1) | Concentration (g · kg−1) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
Total-N | Total-P | K+ | Ca2+ | Mg2+ | ||||||
2019 | 2020 | 2019 | 2020 | 2019 | 2020 | 2019 | 2020 | 2019 | 2020 | |
NZN (control) | 27.9 a | 23.9 b | 2.7 a | 2.0 b | 19.7 a | 17.6 a | 33.66 a | 28.32 b | 4.8 a | 4.1 b |
ZnSO4 | 26.3 a | 27.3 a | 2.1 a | 1.7 b | 19.24 a | 20.3 a | 31.62 a | 33.10 a | 3.9 a | 4.3 a |
Zn-EDTA | 24.7 a | 25.4 a | 2.7 a | 1.8 b | 17.0 a | 22.2 b | 31.10 a | 32.14 a | 3.8 a | 4.4 a |
ZnO NPs | 24.3 a | 25.9 a | 2.5 a | 1.9 b | 21.4 a | 19.4 a | 30.30 a | 31.14 a | 4.3 a | 4.1 a |
Concentration (mg · kg−1) | ||||||||||
Fe2+ | Cu2+ | Mn2+ | Zn2+ | |||||||
NZN (control) | 139.4 a | 181.9 b | 6.3 a | 5.8 b | 231.0 a | 212.4 b | 48.5 a | 45.3 a | ||
ZnSO4 | 154.9 a | 191.6 b | 6.4 a | 6.2 a | 236.8 a | 233.8 a | 39.6 a | 40.4 a | ||
Zn-EDTA | 160.8 a | 194.5 a | 6.5 a | 6.3 a | 242.4 a | 236.0 a | 35.8 a | 38.0 b | ||
ZnO NPs | 118.3 a | 179.4 b | 6.2 a | 6.6 b | 227.8 a | 241.0 b | 39.3 a | 35.8 b |
Means in the same row followed by the same letters were not significantly different (Tukey’s test,
ZnO NPs, zinc oxide nanoparticles; NZN, nitrazinc, containing Zn(NO3)2 and urea–ammonium nitrate fertiliser; Zn-EDTA, zinc ethylene diamine-tetra-acetic acid; ZnSO4, zinc sulphate.
In most established pecan orchards, soil P is a relatively immobile element, and banding has been used to rapidly ameliorate its deficiency (Smith, 2009). In our study, the Zn spray did not maintain the concentration of P in the leaflets between the years evaluated. Similar results were reported by Naira et al. (2013) with foliar applications of 0.5% Zn (ZnSO4), urea + ZnSO4 (0.5%+0.5%), boric acid + ZnSO4 (0.1% + 0.5%) and the combination of these in ‘Western Schley’ nuts, with values of 1.6, 1.8 and 2.2 mg · kg−1, respectively. In pecan nuts, the information generated for this element with foliar applications of Zn is scarce. However, Zn remained at sufficiency levels for pecan, according to Ojeda-Barrios et al. (2012), with values between 1.05 mg · kg−1 and 1.67 mg · kg−1. On the other hand, with the exception of treatment with Zn-EDTA, no changes in K+ levels were observed. However, in this experiment, no significant changes were observed in kernel percentage, a characteristic associated with the optimal supply of Zn in pecan nut. The results are consistent with those published for ‘Western Schley’ (Ojeda-Barrios et al., 2014) with foliar application of Zn-EDTA (0.76, 1.53 and 2.29 mM). In contrast, lower concentrations of 8.4, 9.1, 8.6 and 11.1 mg · kg−1 were reported by Naira et al. (2013) after spraying with ZnSO4, urea + ZnSO4, boric acid + ZnSO4 and ZnSO4 + amino acids, respectively.
Over the 2 years evaluated, Zn application did not affect the concentrations of Ca2+ (30.4–33.7 mg · kg−1) or Mg2+ (3.8–4.8 mg · kg−1), which – according to Pond et al. (2006) – are in the high and normal ranges, respectively. The leaflets did not present any necrosis related to high calcium concentrations. Mg2+ deficiency has been reported in acid and alkaline soils (Sparks, 1996). The soil characteristics were as follows: pH value: 7.8 and CaCO3 content: 20%. These can interfere with the high concentration of Ca in the soil and can also affect Mg, as indicated by Walworth and Heerema (2019). Among the micronutrients, the concentrations of Fe2+, Cu2+ or Mn2+ were not affected by Zn-EDTA; however, the levels of Cu and Mn were similar to those observed with ZnSO4. Similar behaviour was observed for Cu and Mn in a previous study carried out by Ojeda-Barrios et al. (2014) with Zn-EDTA sprays (0.76, 1.53 and 2.29 mM) over 3 years with young trees (≈8 years old) of ‘Western Schley’.
In general, Zn applications improve nut yield in pecan, but they have also been shown to increase the occurrence of AB (Castillo-González et al., 2019). In our study, Zn applications (NZN, ZnSO4, Zn-EDTA and ZnO NPs) maintained the concentrations of the essential elements with the exception of Zn2+, whereby they did not exceed the control values (Figures 5A and 5B). A similar behaviour was observed by Naira et al. (2013) with foliar ZnSO4 sprays, with maximum values of Zn between 195 mg · kg−1 and 294 mg · kg−1, i.e. under toxic conditions according to Walworth and Heerema (2019). In this sense, cultivated plants can vary their nutrient composition and show optimum growth and development (Cruz-Crespo et al., 2014). Most pecan orchards are established in arid or semi-arid regions, and growers have managed Zn supply through multiple foliar Zn sprays, mainly ZnSO4 and Zn-EDTA, with Zn-EDTA proving more efficient in alkaline soils (Walworth et al., 2017). Other authors such as Smith and Storey (1979) point out that Zn(NO3)2 sprays show better Zn absorption than ZnSO4 for similar doses. In general, the other Zn sources, including NPs, show a similar behaviour. Results can be associated with the relatively high dose and number of applications made. However, foliar application of ZnO NPs at concentrations between 0.1 mg · L−1 and 150 mg · L−1 have been shown to improve the nutritional status of numerous crops including mango (
Plants under abiotic stress activate a defence system that includes antioxidant enzymes (peroxidases, SOD, catalase and ascorbate peroxidase) and antioxidant compounds (phenols, flavonoids, GSH and carotenoids, among others), which can inhibit or reduce the production and effects of reactive oxygen species (ROSs) (Teran-Erazo et al., 2019). These ROSs are associated with oxidative damage and cell death, and in pecan nut trees, they can influence AB by reducing growth and productivity (Ojeda-Barrios et al., 2022). Our study explored the behaviour of some antioxidant enzymes in the leaflets, including SOD, CAT and guaicol peroxidase (GPx) (Table 4). Zinc is a micronutrient that has stabilising properties and protective effects against oxidative and peroxidative damage, loss of integrity and alteration of membrane permeability (Subba et al., 2014). In general, Zn-EDTA spraying significantly reduced the activities of SOD, CAT and H2O2 production. However, ZnSO4 and ZnO NPs showed similar values for CAT and H2O2. These results are likely linked to the activity of Zn as a cofactor for several enzymes, including dehydrogenases, oxidases and peroxidases (Balafrej et al., 2020).
Oxidative metabolism and AC in ‘Western Schley’ pecan tree leaflets sprayed with sulphates, chelates and zinc nanoparticles.
Treatments (200 mg · L−1) | SOD | H2O2 | CAT | GPx | AC |
---|---|---|---|---|---|
NZN (control) | 1.4 a | 0.4 a | 3.5 a | 3.2 b | 83.1 a |
ZnSO4 | 1.3 ab | 0.3 b | 2.3 b | 5.6 a | 80.6 a |
Zn-EDTA | 1.2 c | 0.4 b | 2.3 b | 5.2 a | 76.9 b |
ZnO NPs | 1.3 b | 0.3 b | 2.4 b | 5.3 a | 82.6 a |
Means in the same column followed by the same letters were not significantly different (Tukey’s test,
AC, antioxidant capacity (% of DPPH inhibition); CAT, catalase (nmol GSH · min−1 · g−1); DPPH, 2,2-diphenyl-1-picrylhydrazyl; GPx, guaiacol peroxidase (μmol GSH · min−1 · g−1); H2O2, hydrogen peroxide (μmol · g−1); ZnO NPs, zinc oxide nanoparticles; NZN, nitrazinc, containing Zn(NO3)2 and urea-ammonium nitrate fertiliser; SOD, superoxide dismutase (units · min−1 · g−1); Zn-EDTA, zinc ethylene diamine-tetra-acetic acid; ZnSO4, zinc sulphate.
Applications of200 mg · L−1 Zn increased the activity of GPx (5.19-5.64 nmol GSH · min−1 · g−1), which is associated with a reduction in peroxide production. An increase in GPx activity has been reported with edaphic applications of Zn(NO3)2·6H2O (150, 300 and 600 μM) in
Under abiotic stress, plant cells can increase their AC to minimise the negative effects of oxidative stress on physiological and biochemical processes (Davarpanah et al., 2016). In our study, the values of AC in the leaflets fluctuated between 76.9% and 83.1% of DPPH inhibition, the application of Zn-EDTA standing out among the treatments (Table 4). None of our trees showed symptoms of Zn deficiency, as was also corroborated by the sufficiency range measurements of their foliar Zn. However, in pecan tree, there is little information on Zn spraying and changes in the AC. Subba et al. (2014) indicate that Zn plays important roles in non-enzymatic antioxidant systems and is a micronutrient that helps stabilise the effects of oxidative and peroxidative stress, loss of cell integrity and permeability.
One of the most reliable indicators of stress in plants is associated with the synthesis and accumulation of photosynthetic pigments, where Zn actively participates in their biosynthesis (Subba et al., 2014). The concentrations of the photosynthetic pigments, chlorophyll and carotenoids, are presented in Table 5. With Zn-EDTA, decreased concentration of chlorophyll and total carotenoids was determined, while with ZnSO4 and ZnO NPs, the concentration of chlorophyll and total carotenoids was reduced. Foliar Zn uptake depends on the Zn source. ZnSO4 and Zn(NO3)2 are most common in pecan. Most of the studies on foliar application of ZnO NPs are for vegetables and cereals; there is little information for perennial plants, such as vines and fruit trees, especially not for pecan trees. Previous studies were conducted on the spraying of ZnO NPs as follows: 150 mg · L−1 in the common bean (
Concentration of photosynthetic pigments and phenolic compounds in ‘Western Schley’ pecan tree leaflets sprayed with sulphates, chelates and zinc nanoparticles.
Treatments (200 mg · L−1) | TChl (μg · g−1) | TC (μg · g−1) | TFl (mg GAE · g−1) | TP (mg QE · g−1) |
---|---|---|---|---|
NZN (control) | 45.1 a | 14.7 a | 55.7 a | 18.4 a |
ZnSO4 | 45.5 a | 10.5 b | 53.7 a | 17.1 a |
Zn-EDTA | 41.7 b | 10.7 b | 61.6 a | 20.0 a |
ZnO NPs | 40.7 b | 12.7 ab | 63.6 a | 22.0 a |
Means in the same column followed by the same letters were not significantly different (Tukey’s test,
Among the bioactive compounds that we evaluated in pecan leaflets, TP and TFl did not show significant variation due to Zn application (Table 5). This lack of response may be associated with the metabolic role of Zn, including synthesis of proteins, regulation of carbohydrate metabolism and the activation of some antioxidant enzymes that act against oxidative and peroxidative cell damage (Elsheery et al., 2020). In potato leaves (
For the growing seasons analysed, foliar sprays of ZnSO4, Zn-EDTA and ZnO NPs helped maintain the foliar concentrations of NSCs, nutrients (total-N, Ca and Mg) and kernel percentages of the harvested nuts. Trees sprayed with ZnSO4 better maintained leaflet Zn concentration. It would be worthwhile to determine the optimal Zn dose rates for the various pecan cultivars in common use and also to increase our understanding of the physiological and biochemical changes associated with foliar Zn applications. On the other hand, Zn-EDTA spraying significantly reduced the activities of SOD, CAT and H2O2 production. However, ZnSO4 and ZnO NPs showed similar values for CAT and H2O2. In general, these results are valuable, considering the negative effects of AB in pecan.