Water shortage and salinity are major challenges for maintaining global food security. Using nutrients in a nano-scale formulation consisting of nano zinc oxide (ZnO NPs) is a novel fertilizer strategy for plants. In this study, two field trials were performed in 2018 and 2019 to examine the effects of three concentrations of zinc oxideZnO NPs (0, 50 and 100 ppm) in eggplant grown under irrigated conditions. adequate (100 crop transpiration; ETc) and drought stress (60% ETc). The physiological, biochemical and anatomical responses of the plants were evaluated. Drought-induced stress significantly reduced the membrane stability index (MSI), relative water content (RWC) and photosynthetic efficiency, thereby hindering eggplant growth and yield. In contrast, exogenous ZnO NPs for water-stressed eggplant resulted in increased RWC and MSI associated with improved stem and leaf anatomical structure and enhanced photosynthetic efficiency. Under drought conditions, the addition of ZnO NP 50 and 100 ppm improved growth characteristics and increased fruit yield by 12.2% and 22.6%, respectively, compared with fully irrigated and unfertilized plants nano zinc oxide ZnO NPs. The highest water yield (WP) was obtained when eggplant plants were irrigated with 60% ETc and treated the leaves with 50 or 100 ppm ZnO NP, resulting in a 50.8–66.1% increase in WP compared to non-irrigated plants. enough. Collectively, these findings demonstrated that foliar spraying of ZnO NPs offers utility for alleviating drought-induced effects on saline-grown eggplant.
Sustainable agricultural development depends on the type and availability of irrigation water worldwide, as agriculture consumes about 69% of total freshwater [ 1 ]. Represented, food and water production are closely related, with nearly 40% of agricultural production worldwide coming from irrigated cropland [ 2 ]. In the Mediterranean region, water resources are scarce, which calls for a reassessment of current water uses. Population growth has led to an increase in food demand, and the irrigated area has increased eightfold over the past century [ 3 , 4 , 5]. These constraints and risks to food security will be enormous, especially with projected climate change, causing increasing competition for water between different sectors [ 6 , 7 ]. To undermine future global changes and ensure food security, efforts are being made through investigations to promote water productivity (WP). Therefore, effective innovations in irrigation techniques and management are needed to achieve more rational and efficient water use [ 8 , 9 , 10 , 11 , 12 ]. In this regard, deficit irrigation (DI) is used as a practice to save water by adding less water than is required for irrigation [ 3 ,13 ].
Eggplant ( Solanum melongena L.) is a distinct crop worldwide, with a cultivated area of 1.86 million hectares, producing approximately 54 million Mg. Globally, Egypt ranks third among the largest eggplant producing countries, accounting for approximately 2.6% of world production [ 14 ]. Eggplant requires uniform soil moisture to obtain commercially important yields [ 15 , 16 ]. Although eggplant is considered to be tolerant of moderate water stress [ 17], it is difficult to apply water deprivation measures, especially in arid and semi-arid areas with saline soils that do not productivity reduction. Failure to irrigate the four eggplant cultivars resulted in a drastic reduction in the fresh weight of different plant parts (root, stem and leaf) and leaf water content as well as a decrease in chlorophyll content [ 18 ]. Eggplant fruit yield decreased by 60% when the water deficit increased from 20% to 40% of field area [ 19 ]. Lack of ability to absorb and transport nutrients due to water stress, leading to loss of crop yield. Furthermore, under alkaline soil conditions, the absorption and transfer of nutrients from roots to leaves decreased, especially trace elements [ 20 ].
Zinc (Zn) is a trace nutrient that plays an important role in the growth of all plants. Zn participates in the activity of various enzymes (RNA and DNA polymerase, dehydrogenase, transphosphorylase and proteinase), as well as contributes to the maintenance of membrane structure and cell division, biosynthesis of chlorophyll, and improves plant photosynthetic machine [ 20 , 21 , 22 ]. Foliar application of trace elements is more favorable for crop response at field scale, as it is more environmentally friendly than soil application which may show toxicity when the same trace elements are added. [ 21 , 23]. Micronutrients have been shown to alleviate water stress in plants by enhancing WP, maintaining cellular integrity, and detoxifying drought-induced free radicals [ 24 , 25] ].
In recent years, the incorporation of nanomaterials products in many fields including nanofertilizers is gaining interest. Nanoparticles (NPs) have novel properties since their small size (at least below 100 nm in one dimension) leads to high surface area and surface charge, thus, NPs are more reactive than with partners on a large scale [ 25 , 26 ] . Nanofertilizers are used to gradually release nutrients while minimizing soil pollution [ 27 ]. These nano-sized fertilizers are an approach that helps to deliver nutrients to plant leaves, thereby increasing the efficiency of plant nutrient absorption [ 28 ]. ZnO NPs have been reported to alleviate oxidative damage in various crops [ 29 , 30, 31 ]. ZnO NPs reduce malondialdehyde (MDA) levels and enhance CAT and SOD activities in Leucaena leucocephala under stress [ 30 ]. Similar results were also reported in chickpeas and sugar beets [ 31 ]. One of the benefits of nano-sized fertilizers is to minimize the rate of addition of nutrients, thus saving input costs and reducing the environmental impact of chemical fertilizers in a sustainable way [ 32 ] . Due to their small size, nanofertilizers have higher and faster translocation between plant parts, increasing nutrient efficiency [ 33 ].
Ordinary Zn fertilizers in the form of ZnSO 4 · 7H 2 O have very low Zn utilization efficiency (1–5%). However, zinc oxide nanoparticles (ZnO NPs) were systematically evaluated in plants to enhance their ability to modulate crop yield and nutrient utilization efficiency [ 32 ]. Previously, it has been shown that the use of nano-fertilizers has the ability to promote drought tolerance in some crops; soybeans [ 20 ], corn [ 34 ], and wheat [ 32 ]. According to [ 22], spraying ZnO NP alone or in combination with Cu NP and Mn NP increased basil plant growth, chlorophyll content, as well as enhanced antioxidant activity. ZnO NP modified drought-tolerant sorghum, increased green yield by up to 183%, and improved the plant’s total N and K acquisition [ 25 ].
The combination of deficient irrigation and the application of nano-fertilizers could potentially save significant water and improve WP in eggplant. At the field scale, the responses of eggplant to a combination of deficiency irrigation and foliar application of nanozinc oxide grown on saline acid sulphate soils have not been fully investigated. Therefore, this study aimed to explore the potential effect of foliar application of ZnO NP to improve drought conditions in eggplant. Furthermore, study their effects on eggplant growth, yield, WP, tissue water status, photosynthetic efficiency, nutrient content and anatomical response.
2. Materials and methods
2.1. Test site
Two tests were conducted consecutively during the summer of 2018 and 2019 (April 5 to August 29) in the El Fayoum region (latitude 29°02′ and 29°35N and longitude 30°23 ′ and 31° 05 ′ E), Egypt. The average climate data of this area for the two growing seasons are given in Table 1. A typical clay, silica sand, superheat, humus [ 35 ], and its physicochemical characteristics have been reported. evaluated [ 36 , 37 ] and displayed in table 2 and table 3.
2.2. Application Design and Experimental Processing
The experimental arrangement was a plotting system in a randomized complete block design (RCBD) with three replicates. Double irrigation (full irrigation, FI (100% crop evapotranspiration; ETc) and deficient irrigation, DI (60% ETc)) was applied to the main plots and subplots with three concentrations. ZnO NP (0, 50 and 100 ppm) was foliarly applied twice; 30 days after inoculation and 2 weeks after. Therefore, six treatment methods were used as follows: I 100 (100% ETc), I 60 (60% ETc), I 100 + ZnO NP 50 (50 ppm nanoscale ZnO), I 100 + ZnO NP 100 (I 100 + 100 ppm nanoscale ZnO), I 60 + ZnO NP 50, and I 60 + ZnO NP 100 .
The experimental area is divided into plots. The area of each plot is 15 m long x 0.70 m row width (10.5 m 2 ). Plants are spaced about 30 cm apart, every two plants in rows, each row is 50 plants. 30-day-old eggplant (cv. Hybrid Soma ® ) transplants, secured from the nurseries of the Ministry of Agriculture, were transplanted at a rate of one plant per plant. The drip irrigation system was specified at one line and one hose per plant, providing 3.6 L of saline water (1.88 dS m −1 ;Table 4) per hour. Seedlings were transplanted on April 5 and the trial ended on August 29 (in both seasons). The 3 m wide trench-free areas were designated as the separating boundary between the two irrigation formulations. Seven days after transplanting, irrigation measures are started. Agronomic practices for commercial eggplant production, including control of pests, weeds and diseases were implemented as recommended.
2.3. Applied irrigation water (IWA)
Eggplant seedlings were irrigated with different amounts of water for a period of 2 days until the end of the trial. The crop water requirements (ETc) were determined using the type A pan equation [ 38 ]:
ET c = E pan × K pan × K c
where ETc is the water demand for plants (mm day −1 ), E pan is the amount of evaporation from the type A pan (mm day −1 ), K pan is the coefficient of Pan [ 38 ], and K c is the coefficient Crops.
The amount of irrigation water (IWA) is determined according to the following formula:
IWA = (A × ETc × Ii × Kr) ÷ [Ea × 1000 × (1 – LR)]
where IWA = amount of irrigation water in m 3 , Ea = % of efficiency, LR = washout requirement, A = plot area in m 2 , ETc = crop irrigation water demand in mm per days, Ii = irrigation interval (days) and Kr = coverage factor.
At the end of the trial, 10 plants were randomly taken from each experimental plot and growth characteristics were evaluated. The fourth leaf fully expanded from the top of the stem (and its internodes) appearing after drought stress was taken per plant to evaluate morphological, physiological, macroscopic and micronutrient parameters. nursing and surgery.
2.4.1. Morphological and yield parameters and its components
Plant height, root diameter and fresh and dry shoot weight were recorded (cm) at the end of the trial. Plant leaf area (cm 2 ) was measured using the relationship between leaf area and leaf weight as demonstrated by [ 36 ] with some modifications. Leaf surfaces were thoroughly washed in running water followed by double distilled water, then 10–20 leaf plates (10–20 cm 2 ) were dried in an oven at 85 °C for 24 h to allow dry weight (DDW). The total leaf area −1 of a tree is calculated according to the following formula:
Total leaf area of the tree −1 = (LDW DDW) × DA (1)
where LDW is the total dry weight of the leaves (g), DDW is the dry weight of the plate (g) and DA is the area of the plate.
A total of 50 days after transplanting, five plants were assigned from each experimental plot to weekly record the mean of fruit length (cm), number of fruit −1 plants, fruit weight (g) and total yield. capacity (t ha −1 ) .
2.4.2. Physiological Measurements
Relative water content percentage (RWC, %) was determined based on fresh weight (FM in g), turgid (TM in g), and dry weight (DM in g) of leaf plate. . After measuring the FM of the fresh leaf plates, they were placed in a container (slightly longer than the sample) and distilled for 24 h until constant weight (leaf cling film was wetted with absorbent paper towels) . TM was measured for each sample. DM was obtained after drying these leaves at 70 °C in an oven for 72 h to constant mass. The percentage of relative water content (RWC,%) was determined according to the equation [ 39 ]:
RWC (%) = [(FM – DM) (TM – DM)] × 100
Based on the electrical conductivity of two samples of leaves without midrib, calcined at two different temperatures, 40 and 100 °C for 30 and 10 min (C1 and C2), respectively, the percentage of the index was stable membrane (MSI, %) was determined. according to the equation [ 40 ]:
MSI (%) = [1 – (C1 C2)] × 100
A hand-held sulfur meter (Handy PEA, Hansatech Ltd., Kings Lynn, UK) was used to evaluate the fluorescence ‘ a’ of chlorophyll. The equation F v / F m = ( F m – F 0 ) ÷ F m [ 41 ] is practiced to calculate the PSII maximum quantum yield. Based on equal absorption, the equation included in [ 42] is also practiced to calculate the index of photosynthetic efficiency (PIABS). The SPAD meter (SPAD-502-2900) was used to measure the relative chlorophyll index of eggplant. Possessing an emissivity of 0.98 and a spectral response range of 8–14 μm, an infrared thermometer (Fluk 574, Everett, WA, USA) was used to take the temperature measurements of the canopy.
Water productivity (WP) is calculated as mentioned in [ 43 ]:
WP = [fruit yield (kg ha −1 )] ÷ [amount of water applied (m 3 ha −1 )]
2.5. Micro and macro assessment
Evaluation of plant tissue content of nutrients, N, P, K, Fe, Mn and Zn were evaluated in finely ground, dried eggplant leaves ( n = 10). A Kjeldahl micrometer (Guideline Medic Co., Ningbo, China) was operated to determine the N content according to the methods in [ 44 ]. Based on the method in [ 45 ], the P content was evaluated with molybdenum blue, H 2 MoO 7 S, 8% ( w / v ) NaHSO 3 -H 2 SO 4 , and dilute H 2 MoO 7 as reagents. standard. Atomic absorption spectrometer (Perkin-Elmer, Model 3300) was used to evaluate the contents of Zn, Mn and Fe in the leaves as described in [ 46 ].
2.6. Anatomical features
The leaf and stem specimens are held tightly from the middle internode to its leaf blade. Selected specimens were selected from flowering stage plants for killing and fixed for 48 h in 100 mL FAA solution containing 50 mL C 2 H 5 OH (95%), 5 mL glacial acetic acid, 10 mL formalin, add 35 mL of distilled water. Then the samples were exposed to washing with C 2 H 5 OH (50%). Then, dehydration and clearance were performed with a stream of ordinary butyl alcohol, and dipped in paraffin wax (54–56 °C mp). A rotating microtome was operated to cut the bonded 20 μm thick cross-sectional samples (Haupt’s binder). Then the samples were stained with crystal violet-erythrosin combination [ 47]. Slide imaging was performed and then read with a micrometer eye lens to obtain various anatomical features expressed in µm.
2.7. Data analysis
The Gen Stat GLM procedure (version 11) (VSN International Ltd., Oxford, UK) was used to analyze the experimental data. The homogeneity test of variance was performed as stated in a method described by Gomez and Gomez [ 47 ]. Data from the two seasons were analyzed in combination, and across means, differences were compared using Duncan’s Multiple Range Test at the 5% probability level ( p ≤ 0.05).
3.1. Changes in eggplant growth through foliar application of nano zinc oxide and inadequate irrigation
Eggplant growth in terms of plant height, number of leaves per plant, stem diameter, fresh and dry weight of shoots, and total leaf area of the plants were significantly affected by ZnO NP foliar application under irrigated conditions. deficiency (DI) (Table 5). In this respect, DI reduced plant height by 16.3%, leaf count by 23.7%, stem diameter by 7.7%, fresh shoot weight by 25.8%, dry shoot weight by 24.2% and area leaf area decreased by 27.4% compared with fully irrigated plants. These growth characteristics were significantly increased by foliar application of zinc oxide nanoparticle and these improvements were more evident when ZnO NP (100) zinc oxide nanoparticle was used. The use of exogenous ZnO NP zinc oxide nanoparticles alleviated the negative effects of DI stress on eggplant growth, in the sense that ZnO NP (50 or 100 ppm) spraying of plants under DI conditions gave values similar to or higher than those obtained under fully irrigated plants that did not provide ZnO NP (FI + ZnO NP (0) ).
3.2. Changes in photosynthetic efficiency and tissue water status by nano zinc oxide foliar fertilization and deficient irrigation
The efficiency index (PI) of photosynthetic efficiency and relative chlorophyll index (SPAD) were reduced by 22.2% and 5.9%, respectively, under DI conditions (60% ETc) compared with plants grown in FI condition (Table 6). Comparing untreated ZnO NP plants, the PSII maximum quantum yield of photochemical value ( F v / F m), PI and SPAD was increased with ZnO NP (50 or 100 ppm). The application of nano zinc oxide (50 or 100 ppm) to drought-stressed plants increased the values of F v / F m , PI and SPAD and recorded similar values for plants without FI treatment. Water status of eggplant in terms of RWC and MSI was negatively affected by water stress with 40%. However, both RWC and MSI increased by 11.3% and 4.8% (mean) respectively in the ZnO NPN-treated plants compared with the untreated plants (Table 6). Spraying of ZnO NPs (50 or 100 ppm) alleviated the adverse effects of drought stress through increasing RWC and MSI as was the case observed under FI conditions without the use of ZnO NPs (Table 6).
3.3. Changes of eggplant yield and water yield in response to foliar application of nano zinc oxide ZnO NPs and deficient irrigation.
The results on average fruit length, individual fruit weight, total fruit −1 plants, total fruit yield, and WP responses to DI, ZnO NP exogenously applied, and their interactions are presented in Table 7. . Reducing irrigation to 60% ETc significantly reduced fruit length by 9.2%, fruit weight by 18.3%, and fruit number of plants −1 by 8.0% compared to FI. Plants treated with ZnO NP with 50 or 100 ppm ZnO NP showed the greatest fruit length and weight, and total number of fruit −1 compared with untreated plants. Spraying of 100 ppm nano zinc oxide for drought tolerant eggplant showed similar values for fruit length and mean fruit weight for FI tolerant eggplant without nano zinc oxide (FI + ZnO NP (0)). However, water strained eggplant supplemented with 50 or 100 ppm nano zinc oxide produced 25.6% and 33.1% higher fruit numbers, respectively, than FI + ZnO NP (0) .
Exposure to water deprivation significantly reduced fruit yield by 17% compared to FI, fruit yield was also affected by exogenous application of 50 or 100 ppm ZnO NP, increasing by 42.4% and 63, respectively. 4% compared with DI × ZnO NP (0). The highest fruit yield corresponded to the integrated application of 100 ppm nano zinc oxide and FI treatment. However, a combination of 50 or 100 ppm exogenous ZnO NP and lack of water at 60% ETc resulted in 12.2% and 22.6% higher fruit yields, respectively, than those obtained with FI + ZnO treatment. NP (0) . As shown in Figure 2, the regression analysis between fruit yield and ZnO NP concentration was a curvilinear relationship, showing that fruit yield increased with increasing ZnO NP concentration.
The results of Table 7 reported that WP was significantly affected by irrigation regimens, nano zinc oxide supplementation, and their interactions. The level of water shortage is less than 40%, WP increased by 9.9% compared to FI. Meanwhile, application of exogenous nano zinc oxide ZnO NP with 50 and 100 ppm increased WP by 49.1% and 69.8% compared to DI × ZnO NP (0) . The highest WP was obtained when plants were irrigated with 60% ETc and foliar sprayed with 50 or 100 ppm ZnO NP, which increased 50.8–66.1% WP when compared with FI + ZnO NP (0) .
3.4. Changes in nutrient content in response to foliar application of nano zinc oxide and inadequate irrigation
The macronutrients (i.e. N and K) and micronutrients (such as Zn, Mn and Fe) of eggplant leaf tissues were significantly reduced under 40% water deprivation, while P content was not affected. affected by the irrigation regime (Table 8). Compared with untreated ZnO NPs, nano-spraying of zinc oxide (both 50 or 100 ppm) to eggplant increased the content of macronutrients such as N, P, K and micronutrients such as Zn, Mn and Fe (Table 8). In water-stressed eggplant leaf tissues, the micro and macroscopic concentrations were markedly increased by the addition of ZnO NPs. Among the ZnO NP applications, DI × ZnO NP (100) exhibits 21.6% higher N, 91.4% P, 9.4% K, 65.0% Zn, 27% Mn. and Fe 6.6% when compared with FI × ZnO NP (0) (Table 8).
3.5. Anatomical responses of leaves and stems to foliar application of nano zinc oxide and inadequate irrigation
The data presented in Table 9, Table 10, Figure 3 and Figure 4 show that lamellar thickness, midrib length and thickness, and vascular bundle length and width all decrease with DI × ZnO NP ( 0) . However, the use of 100 ppm exogenous zinc oxide nanoparticles minimized the deleterious effects of DI stress on eggplant, in view of the higher or similar values of leaf anatomical characteristics observed when compared with eggplant. compare with FI × ZnO NP (0) . The largest anatomical features such as length and width of the stem, length and width of the abutment, size of the tube (length and width), sheath thickness, and abutment thickness were recorded. again equal to FI × ZnO NP (100) , while the lowest values correspond to DI × ZnO NP (0) (Table 10 and figure 4). However, foliar application of ZnO NP (100 ppm) improved the anatomical features of DI stems when compared with FI × ZnO NP (0) .
Drought is one of the main constraints of irrigated agriculture, severely affecting crop production, thereby threatening food security [ 7 , 48 ]. These threats to the sustainability of food production are exacerbated by increasing droughts in arid regions, including Egypt, particularly when synchronizing with saline-alkaline soils. [ 49 , 50 , 51]. The combination of salinity-drought stress can limit plant growth by affecting a number of biochemical and physiological processes and causing nutrient deficiencies. As a result, these stressors can cause significant yield losses. The technique of making adjuvants in the formulation of nanoparticles such as zinc oxide nanoparticles is being considered as a fertilizer, as well as being able to create drought tolerance [ 32 , 34 ].
The present study demonstrated that reducing irrigation to 60% ETc resulted in eggplant exposure to persistent severe water shortages. This water stress causes loss of membrane integrity and tissue dehydration, as well as disrupts the photosynthetic capacity of PSII and reduces the relative chlorophyll content (Table 6), thereby reducing significant growth-related traits, i.e. shoot length, number of leaves −1 , stem diameter, fresh and dry shoot weight, and total plant leaf area (Table 5). The primary response to soil water deficiency is stomatal closure via root-to-bud (primarily ABA) signals, which directly affect CO2 diffusion into leaf tissues, reducing photosynthesis. synthesis and reduced growth of eggplant [ 52 , 53 , 54 ]. Stressors such as drought and salinity severely inhibit plant growth and yield through inducing upregulation of cyclin-dependent kinase enzyme activity, resulting in fewer meristocytes proliferation and cell division and expansion [ 55 , 56 , 57 , 58 , 59 ], thereby reducing leaf number and leaf area (Table 5), which coincided with a corresponding decrease in chlorophyll index. and photosynthetic efficiency of PSII (Table 6). Our results demonstrated that using exogenous ZnO NPs improved growth-related parameters of drought-stressed eggplant. This growth promotion in ZnO NP-treated plants is most likely related to the effects of nano zinc oxide ZnO NPs on hormonal signals that regulate root structure to improve plant adaptation to deficient soils. water [ 32 ]. Indeed, ZnO NP enhances the activity of genes/expression-related hormones such as ABA and cytokinin, and at the same time regulates root development that helps to withstand drought stress [ 60 ]. Furthermore, foliar spraying of ZnO NPs can enhance the recovery of photosynthetic efficiency, thus can provide more metabolites/photosynthetic substances for eggplant growth.
Reduced soil water availability and soil salt accumulation cause abscisic acid (ABA) accumulation in plant tissues, causing osmotic stress [ 16 , 61 , 62 ] and loss of cell transport capacity due to lower amount of water for cell expansion, thus reducing RWC. Furthermore, a decrease in MSI was observed in DI stressed eggplant, possibly due to oxidative stress stimulated by excess production of reactive oxygen species (ROS) in plant organelles [ 50 , 63 , 64 ], which induces lipid peroxidation leading to reduced membrane integrity and loss of cell turbulence, suggesting that DI-stressed eggplant leaves undergo membrane degradation [65 , 66 , 67 ]. However, drought-induced damage to cell membranes and reduction of tissue water content were alleviated by exogenous zinc oxide nanoparticle (Table 5), which agrees with the observations of [ 68] in corn. The water state of eggplant tissue was promoted in water-stressed plants due to zinc oxide nanofoliage, demonstrating that ZnO NPs can play a role in maintaining cell membrane integrity and increasing RWC under metabolically available aqueous form, which may reflect metabolic processes in plants [ 69 ].
Besides reducing leaf chlorophyll index (SPAD), severe water stress reduces photosynthetic efficiency such as PSII maximum quantum yield ( F v / F m ) and electron flow rate through PSII. (PI; Table 6). Chlorophyll concentration is related to photosynthetic efficiency [ 70 , 71 , 72 ], so the observed decrease in photosynthetic efficiency is related to chlorophyll depletion [ 12 , 73 ], as occurred in this study (Table 6). Water deprivation induced degradation of protein D1 converting to a lower value of F v / F m representing photoinhibition [ 74 ], suggesting that damage occurs in the light-harvesting complex of F v / F m . PSII in drought-stressed eggplant. According to our results, exogenous ZnO NP improved the drought tolerance of eggplant, suggesting that ZnO NP increased the SPAD value concurrently with the increase of the chlorophyll fluorescence apparatus (Table 5). These positive findings by foliar application of ZnO NPs may be due to stabilization of membrane integrity and increased RWC (Table 6) as well as increased micro and macroscopic uptake (Table 8) [ 75 ] and interferes with the activity of the enzyme chlorophyllase [ 76 ] to maintain chlorophyll [ 77 ], thereby increasing the efficiency of photosynthesis. Together with this line, the authors of [ 34 ] reported that the administration of 100 mg L -1 ZnO NP promoted ultrastructural stabilization of the chloroplasts and mitochondria of water-stressed maize, which increased the efficiency of the chloroplasts and mitochondria. photosynthesis fruit. This may be related to the accumulation of osmotic substances such as proline and sugar content for osmotic regulation function.
In this study, drought stress reduced fruit yield and its composition (Table 7), agreeing with the results obtained for eggplant [ 15 ], tomato [ 51 ] and cucumber [15 ] 78 ]. Accordingly, they discovered a decrease in mean fruit weight, total fruit count and total fruit yield when the plants were under water stress. Under drought conditions, exogenous ZnO NPs improved eggplant water status, PSII efficiency, and eggplant growth and biomass, reflecting a significant increase in fruit yield and characteristics. fruit scores (number, weight and length) (Table 7). Favorable results were obtained showing that 100 ppm ZnO NP (at recommended concentrations) was more effective, in the sense that the highest yield was observed when fertilizing fully irrigated or deficient plants. Taken together, these results confirm previous reports [ 79 ] that found that plants require micronutrients in addition to macronutrients for higher growth potential and yield. . Together with these lines, the authors of [ 25 ] demonstrated that the yield of sorghum seeds grown under water stress can be increased by up to 183% by ZnO NP. Under water-constrained conditions, the main objective was to save significant water and increase WP [ 3], which was increased by 9.9% by DI in the present study, however, this improvement in WP amounted to 66 % by spraying DI stressed eggplant with ZnO NP (Table 7). In [ 27 ] similar findings were also reported, showing that seed-based WP and biomass were increased by the addition of ZnO NPs to sunflowers grown under 50% irrigation restriction. ZnO NP supplementation induced changes in plant root morphology, increased lateral root formation [ 60 ], and root biomass [ 25 ] presumably increased water uptake.
Our results showed that plants grown under water-restricted conditions had lower concentrations of N, K, Zn and Mn, with the exception of P (Table 8). The lack of soil moisture reduces the diffusion of nutrients around the roots as well as nutrient uptake by reducing active transport, transpiration flux and membrane permeability [ 80 ]. In sorghum, application of nano zinc oxide ZnO NPs to the soil or foliar pathways increased nutrient concentrations (N, P, K, Zn and Mn), as occurred in this study (Table 7) [ 81 ]. However, the concentrations of macronutrients and micronutrients in leaves were adjusted by foliar application of ZnO NP (especially for 100 ppm, Table 8). Therefore, our results indicate that drought stress has deleterious effects on the nutritional content of eggplant, however, exogenous ZnO NP is associated with alleviation of these negative effects. this. Previous studies have described that nano zinc oxide can increase the macro and micronutrients in pinto beans [ 82 ] and sorghum [ 25]. In addition to the improvements in film stability and plant water status, the improved nutritional status of eggplant by exogenous zinc oxide nano makes it possible for eggplant to reduce the effects of DI stress on growth. its growth and productivity.
Plant processes involve the genetic, physiological, biochemical and anatomical mechanisms responsible for crop yield, functions of which are related to the internal anatomical structures of plants [ 83] ]. These enhanced properties (e.g. growth rate, yield, SPAD value, photosynthetic capacity, water relationship, WP and nutrient content) in response to externally applied ZnO NPs have may be associated with improved stem and leaf anatomical features (Tables 9 and 10; Figures 3 and 4). Foliar application of ZnO NP increased leaf and stem anatomical parameters of eggplant grown under deficient irrigation conditions, possibly due to improved RWC, membrane stability and nutrient status [ 75] , 84 ].
According to the findings obtained in the present study, foliar fertilization with nano zinc oxide (ZnO NPs) could be a promising method to improve drought tolerance in eggplant grown on saline soils. These positive effects mainly came from improved macro and micronutrient uptake, increased relative water content (RWC), decreased membrane damage (MSI), as well as increased Anatomical characteristics of leaves and stems of eggplant. The eggplant supplemented with nano zinc oxide improved the SPAD value and the chlorophyll fluorescence device ( Fv / Fm and PI). All these factors collectively contribute to the better growth and yield of eggplants grown under irrigated conditions. It is important to note that the use of ZnO NP for foliar spray for eggplant increased water yield. Therefore, our findings have shown the utility of using ZnO NPs (100 ppm) to ameliorate the effects of water stress on eggplant production in dryland agriculture.
Reference source: Foliar Application of Zinc Oxide Nanoparticles Promotes Drought Stress Tolerance in Eggplant (Solanum melongena L.)