A Contemporary Review of Preharvest Mineral Nutrient Management and Defense Elicitor Treatments for Robust Fresh Produce

Abstract

Supplying fresh produce that meets consumers’ needs necessitates production of robust fruit and vegetables. However, supply chains can struggle to deliver robust produce, especially for delicate leafy vegetables. Interacting preharvest genetic, environment, and management factors influence product robustness at harvest, with subsequent implications for perishability, including food safety. Fresh produce quality typically cannot be improved after harvest. This review explores preharvest interventions to optimize robustness at harvest. It overviews conventional, new, and emerging strategies. It considers mineral nutrient management along with chemical and physical elicitors. It also explores approaches to measure and monitor fresh fruit and vegetable robustness, particularly hyperspectral technologies. Recommendations are proffered for future research towards enhanced fresh produce robustness, particularly leafy vegetables, through preharvest management. Optimizing robustness is fundamental to efficient, effective, and sustainable fresh produce supply chain management, thereby contributing to food security and consumer satisfaction and wellbeing.

1. Introduction

Meeting increasing demand for producing high quality, safe and nutritious food which satisfies consumers’ requirements and expectations relies on effective and sustainable fresh fruit and vegetable supply chains. Demand is increasingly attuned to assuring high-quality, safe, and nutritious food [1,2,3,4], such as leafy vegetables [5,6]. Yet, despite growing demand, the quality of nutritious fresh fruit and vegetables remains inconsistent, including its safety. For example, outbreaks of food poisoning and recalls of leafy vegetables, including microgreens [7,8]. Concern over health risks to consumers from food poisoning has been linked with the proliferation of microbes on and in mechanically damaged plant tissue [9,10]. Hence, it is important to maintain robust fresh produce that withstands both abiotic and biotic stresses at harvest and ultimately satisfies consumers’ needs and wellbeing.

The quality of fresh fruit and vegetables is determined by a combination of physical and chemical factors plus sensory attributes that contribute to desirability for consumption, including market value, safety and overall consumer satisfaction. Irregularities in quality are associated with a range of contributors including less nutritious crops, cultivar selection, reliance on intensive chemical-based fertilizer and pesticide farming practices, and imbalances in mineral nutrition often associated with declining soil structure and fertility [11]. This situation is further compounded by the inherent perishability of fresh horticulture produce and complex handling processes after harvest. The supply chain starts at production. Hence, addressing the challenge is rooted in producing robust fresh produce at harvest. Robust produce should be sufficiently resilient to withstand pressures imposed by the supply chain at harvest, postharvest treatments, storage, distribution, and other marketing rigors imposed by consumers [2].

Robustness for fresh produce may be characterized as inherent qualities that mitigate product stress and injury during handling and distribution, thereby conferring relative tolerance to treatment and handling conditions that negatively affect product quality [12]. However, robustness is not a well-defined quality, including in terms referring to reliable robustness indices [13,14]. Thus, developing indices to maintain and assure optimum quality remains an opportunity within fresh produce supply chains [14]. Robustness attributes at harvest may include intrinsic properties such as firmness, storability, balanced nutrient composition, high nutritional quality, specific bioactive constituents, and relative resistance to pest, disease, mechanical, and physiological disorders [12,14,15,16]. This review defines fresh produce robustness as the relative ability to withstand biotic and abiotic stresses while maintaining desired organoleptic qualities, including physicochemical and nutritional quality and general durability to endure logistical processes throughout the supply chain. These ideal attributes ensure robust fresh produce that meets consumer satisfaction and well-being.

A holistic approach that incorporates preharvest practices, processes, and strategies plays a pivotal role in producing harvestable high-quality robust fresh produce meeting the desired standard [17]. In this review, preharvest strategy is defined as a management approach or intervention that can influence the relative robustness quality of fresh produce at harvest and under postharvest handling. It encompasses general management practices, particularly optimized nutrient management, and specific interventions with defense elicitors, notably chemical, physical, and electromagnetic approaches, including radiation. Optimizing each preharvest input within an executable production strategy is key to achieving the expected outcome. However, studies reporting the integration of preharvest strategies aimed at delivering robust produce at harvest, able to endure pressures imposed throughout the supply chain are relatively limited. This review critically assesses the range of preharvest strategies that proffer robust fruit and vegetables, particularly relatively delicate leafy vegetables, for consumers’ satisfaction and well-being. It considers chemical approaches and mineral nutrient management, addresses bioactive agents, like chemical elicitors, and covers physical approaches, including radiation. It also explores rapid and accurate means to measure and monitor fresh vegetable robustness, including hyperspectral technologies.

2. Optimizing Preharvest Strategies to Produce Robust Fresh Produce

Optimized production practices and implementing effective preharvest interventions are particularly important, as crops are continuously exposed to a range of multifactorial environmental stresses. These include biotic pressures such as pathogenic microbes and insect pests, as well as abiotic stresses such as drought, heat, ultraviolet light, chilling, water logging, heavy metals, and salinity [18]. There are various approaches to producing robust and high-quality fruit and vegetables, including using chemical approaches. These include mineral nutrient management, bioactive methods such as the application of chemical elicitors (e.g., salicylic acid, jasmonates) and physical techniques such as electromagnetic irradiation approaches. Figure 1 depicts preharvest strategies for producing robust fresh produce that meets consumer expectations of organoleptic satisfaction and personal well-being. It represents nutrient management and elicitors toward protecting plants from environmental stressors through inherent defense mechanisms that include constitutive and induced resistance. Induced resistance involves expression of defense genes and attendant accumulation of defense-related compounds against abiotic and biotic stressors in the environment [19,20,21]. Constitutive resistance typically provides structural protection, alongside preformed defense compounds [22]. Both mechanisms make plant tissue relatively more resistant to production and subsequent postharvest challenges by providing robust fresh produce at harvest.

However, the efficacy of such preharvest strategies is influenced by a variety of multifaceted preharvest factors. These include preharvest genetic potential, interacting with the production environment and management practices, onto which unforeseeable challenges (e.g., inclement weather) and various stresses (e.g., wind damage, heat stress) are superposed. All these factors modulate product robustness at harvest, with direct implications for perishability and quality. Although numerous studies have evaluated individual and some integrated preharvest strategies, relatively few studies have focused on producing robust fresh produce at harvest.

2.1. Plant Nutrient Management

Plant nutrient management is a key strategy for mitigating adverse effects of both biotic (e.g., pests and diseases) and abiotic (e.g., drought, extreme temperature, nutrient deficiency) stresses [23]. Nutrients play a multifaceted role in enhancing plant defence mechanisms by inducing resistance and reinforcing constitutive resistance, both of which are critical for producing robust and high-quality fresh produce at harvest. Induced resistance is a physiological state of enhanced defensive mechanisms upon appropriate elicitation. It involves significant modification in defence gene expression and attendant secondary and primary metabolite levels via synthesis and accumulation of defence-related compounds against stresses [19,20,21]. Application of nutrients such as potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) can modulate defence responses in tomato plants, including defence gene activation, membrane leakage, production of reactive oxygen species (ROS), and ethylene synthesis [24]. Similarly, boron (B), copper (Cu), manganese (Mn), and phosphorus (P) have been shown to influence resistance in cucumber plants against powdery mildew by inducing the systemic production of peroxidase and β-1,3-glucanase, enzymes critical for pathogen suppression [25].

On the other hand, nutrients such as B, Ca, Mn, and silicon (Si) play pivotal roles in reinforcing structural cell wall and membrane partitions essential for maintaining cell and tissue mechanical stability and integrity against environmental stresses [22]. These physical barriers, alongside preformed chemicals (e.g., antimicrobial compounds, phytoalexins, and phenolics metabolism, antioxidant enzymes) constitute inherent or constitutive resistance [22]. Inherent constitutive resistance is relatively long-lasting resistance, providing physiochemically robust fresh produce at harvest towards improved postharvest quality and product resilience.

Both resistance mechanisms, induced and constitutive, as influenced by mineral nutrients, affect not only disease tolerance, but also the inherent quality or condition of fresh produce at harvest. Foliar applications of Ca, zinc (Zn) and B alone and in combination improved yield, quality and antioxidant levels and reduced physiological disorders of tomatoes [26,27]. Most studies on plant defence focus on induced defence mechanisms. Studies on constitutive mechanisms tend to be focused on herbivore resistance [28]. Relatively few studies have comprehensively delved into the interplay between nutrients and both induced and constitutive defence mechanisms, particularly in the context of producing high-quality and robust fresh produce. Existing studies predominantly focused on fruit vegetables and tree fruits (e.g., pome fruit) with relatively limited extension into leafy vegetables, which suggests an opportunity for further research.

2.1.1. Nitrogen

The availability of nitrogen (N) has been identified as a limiting factor in plant defence resistance [20]. Optimizing N fertilizer can induce resistance, influencing both localized defence responses and systemic resistance by promoting defence-related enzymes and proteins [29]. Additionally, N modulates ROS production and signalling in response to abiotic stress, which ultimately affects growth, development, and quality of fresh produce [30]. The N influence on fresh produce quality is mediated by factors that include source, concentration, crops, and host–pathogen interaction [29,31,32]. Appropriate N application results in stress tolerance, enhanced vigorous growth and improved quality of fresh produce [30,33,34]. For instance, a moderate N level is important for high yield and good quality in crops like tomato (230 kg ha⁻¹) [30], baby spinach (200 mg kg⁻¹) [35] and pomegranate (40 mg L⁻¹) [36]. A moderate N application supports optimal growth under stressful environments such as high temperatures by enhancing photosynthesis, N efficiency, and nutrient availability [30].

Table 1. Quality attributes of fresh produce that are positively affected by plant mineral nutrients.

Nutrient	Effect	Produce	References
Nitrogen	Increase total soluble solids, leaf chlorophyll, photosynthesis efficiency, antioxidant enzyme activity, anthocyanin, phenolics, flavonoids, lycopene, antioxidant capacity fresh weight and vitamin C	Apple, blackberry, tomato, spinach	[33,34,35,37]
Calcium	Improve color, enhance shelf life, reduce weight loss, maintain anthocyanin, retain sensory quality, firmness, increase total phenolic content, TSS, vitamin C, reduce deterioration, pathological (e.g., brown rot, anthracnose) and physiological diseases (e.g., spongy tissue, peel creasing scab, bitter pit, blossom end rot)	Plum, blueberry, tangerine, guava, peach, papaya, mango, orange, tomato, green pepper, broccoli microgreens	[6,38,39,40,41,42,43,44,45,46,47,48,49]
Silicon	Increase dry matter content, fruit weight, firmness, TSS, decrease shriveling, respiration rate, improves color, increase total phenolic, total anthocyanin compounds, resistance to disease (e.g., early blight), increase chlorophyll	Nectarine, raspberry, blueberry, apples, tomato, and pepper.	[50,51,52,53,54,55,56]
Potassium	Improves protein, ascorbic acid, lycopene, TSS, reducing sugar levels, titratable acidity, increases total phenols, total antioxidants activity, total flavonoids, vitamin C	Tomato, spinach	[57,58]
Phosphorus	Increase total phenols, total antioxidants activity, total flavonoids, vitamin C, dry biomass of stems and leaves	Spinach, tomato	[57,58]
Magnesium	Increase anthocyanin, vitamin C, carotene, protein content, firmness	Apple, tomato	[59,60]
Iron	Increase dry matter, TSS, total acidity, ascorbic acid content, vitamin A, chlorophyll content	Tomato, leafy vegetables (e.g., mustard, onion)	[5,61]
Molybdenum	Increase fresh weight, polyphenol content ascorbic acid	Tomato, lettuce, escarole, curly endive	[62,63]
Boron	Inhibit powdery mildew, improve shelf life, fruit firmness, increase ascorbic acid, protein and starch	Cucumber, tomato, cauliflower, cowpea, okra	[25,64,65]
Manganese	Inhibit powdery mild, reduce heat-damaged fruit	Cucumber, bell pepper	[25,66]
Copper	Inhibit powdery mildew, increase firmness, fruit juice, TSS, ascorbic acid	Pear, cucumber,	[25,67]
Zinc	Reduce rotting rate, browning, maintain colour, cellulose, pectin, flavonoid, and phenolics, increase ascorbic acid, total antioxidant activity, TSS, titratable acidity, anthocyanin	Longan, apple, strawberry	[67,68,69]

summarizes various quality attributes that are positively affected by plant mineral nutrients.

On the contrary, imbalanced N, whether excess or deficient, disrupts the physiological balance of plant growth, resulting in increased production of reactive oxygen species that cause damage to the cell membrane [36]. For example, low N compromises fruit quality, whereupon fruit may become smaller, lighter in color, prone to sunburn, affected by malformities, and have lower total soluble solids, acidity, and anthocyanin levels [36,70]. In contrast, higher N levels were shown to improve stem yield and vitamin C content in lettuce [40] and vegetative growth in sweet pepper [41]. N has been reported to suppress constitutive resistance, including structural defence and the synthesis of antimicrobial phytoalexins. [29]. This is evident in weakening structural defence resulting in decreasing firmness of various fruits and increasing susceptibility to diseases with its increasing concentration [70,71,72]. Excess N has also been associated with increased blemishes along with lower levels of total, reducing, and non-reducing sugars and decreased ascorbic acid content [72,73]. Excessive N can predispose early senescence, calcium deficiency and susceptibility to diseases, especially with low calcium levels, such as is the case for Pak Choi [74]. Maintaining optimal levels of N and managing N relative to other nutrients, particularly Ca, is evident in lower body rot and stem end rot in avocados [13] and physiological disorders in mangoes such as spongy tissue, jelly seed, internal flesh breakdown, soft nose [14].

Additionally, N sources like nitrate (NO₃⁻) and ammonium (NH₄⁺) differentially affect productivity, quality, and stress responses. Some species favor one form over the other or benefit from a balanced ratio [75,76]. Moreover, environmental conditions can affect plant preferences for nitrogen sources. For tomato seedlings, the optimal ratio of 50:50 NO₃⁻ to NH₄⁺ was favorable against chilling stress conditions as compared to a 75:25 ratio in non-chill stressed plants, possibly due to lower energy demand for ammonium assimilation [77]. Thus, it is prospectively opportune to optimize N levels and ratios of NH₄⁺ to NO₃⁻ to optimise the productivity and quality of fresh vegetable crops such as spinach, tomato and sweet pepper. N expectedly plays an pivotal role in maximizing the yield and quality of fresh produce. However, how N influences the elicitation of resistance against biotic and abiotic stresses merits further elucidation to optimize prospective benefits.

2.1.2. Calcium

Ca also plays a critical role in determining fresh produce quality due to its structural roles in cell wall and cell membrane integrity [78] in addition to being a signalling molecule in plant cell and organ developmental and physiological processes, including responses to abiotic and biotic stresses [79,80]. Through both constitutive and induced resistance, Ca enhances plant resilience and supports high-quality produce at harvest. Ca has been associated with reduced susceptibility to various diseases in fresh produce such as brown rot [42], leaf and fruit scab [46], and anthracnose [43]. The efficacy of Ca in disease management is attributed to maintaining cell wall integrity, serving as a primary barrier against pathogens, as well as being a signalling molecule in countering cell wall damage during pathogen attack [80]. Ca adequacy offers promise towards reduced reliance on fungicides. However, further research is needed to confirm and optimize efficacy in pre- and postharvest systems, especially in leveraging the benefits of both induced and constitutive defence provided by Ca.

Supplementation of Ca has been a critical tool in mitigating physiological disorders, otherwise known as non-parasitic disorders, associated with low Ca levels in fruit and vegetables. Ca deficiency has been linked to maladies such as bitter pit in apples [81], fruit cracking in citrus [45], spongy tissue in mangoes [44], and blossom-end rot (BER) in tomatoes [48]. These disorders reflect Ca’s critical role in cell membrane and cell wall integrity. Inadequate Ca disrupts Ca²⁺ homeostasis, leading to localized membrane degradation and tissue collapse [44,82].

Preharvest Ca application has been reported to increase Ca content in fresh produce to maintain quality [6,83]. Ca consistently enhances fruit firmness, a key factor in consumer acceptability and shelf life. It reduces cell wall degradation, enhances antioxidant levels, and inhibits wound-induced ethylene production, thereby alleviating the impact of mechanical injury after harvest [49]. Also, it decreases stomata size in the epidermis of Chinese cherry, resulting in decreased fruit respiration and transpiration [84]. Concomitantly, it maintained soluble sugars, titratable acidity, vitamin C content, antioxidant enzymes, lycopene, phenolic content and antioxidant activity in tangerine and guava [40,41]. Such effects of Ca on maintaining the quality and robustness of fresh produce have been reported to persist during postharvest storage [40,41,43,83]. The benefits of Ca toward producing robust fresh produce are primarily reported for fruit. It stands to reason that there are potentially unrealized opportunities in understanding and utilizing these physiological and biochemical mechanisms towards delivering relatively more robust vegetables, including leafy and microgreen types.

The efficacy of Ca is influenced by factors such as timing, source, concentration, and of application method. Increasing levels of Ca have been associated with improved fruit Ca concentration, texture, and flavor and decreased weight loss, Mg content, and disease incidence, along with longer shelf life [38]. Enhanced quality and antioxidant content were discerned in cauliflower heads treated with relatively high levels of calcium nitrate (1.5%), calcium chloride (0.9%), and calcium lactate (1.5 g L⁻¹) [85]. The high solubility of some Ca sources, such as calcium chloride, enhances mineral absorption, suggesting that they are absorbed relatively more efficiently [86]. Additionally, the anion may contribute to improving resistance against pathogens [46].

When applied in early stages of development in fruit, Ca effectively maintained postharvest quality and reduced deterioration, including via increased total phenolic content and decreased polygalacturonase activity favouring cell wall integrity [39,47]. In vegetables, continuous application from seedling to harvest improves quality in broccoli [6]. Repeated weekly applications of Ca following fruit initiation were found to improve postharvest quality in tomato [48]. For controlling bitter pit in apple, the efficacy of Ca partitioning into the fruit may be improved by increasing the number of sprays closer to harvest [87]. Compared to soil application, foliar application has been reported to enhance Ca efficacy in maintaining the quality of fresh produce [87,88]. Foliar application notionally obviates low and slow mobility of Ca within plants and provides a rapid and targeted approach to meet Ca demand in critical growth stages [88]. Considering the various influencing factors and understanding the mechanism by which Ca improves the quality of fresh produce permits the prescription of effective and sustainable, robust fresh produce production strategies.

2.1.3. Silicon

Silicon (Si) has been reported to positively mediate physiological, biochemical and antioxidant metabolism in plants to alleviate impacts of adverse growth conditions (Table 1) [89]. Silicon’s supposed modes of structural and membrane integrity action are reflected in greater firmness in fruit and decreased pathogen infection [50,51,52,53,55,90]. It may strengthen the waxy bloom, potentially protecting blueberry fruit during harvest and postharvest handling and prospectively delaying pathogen infection of strawberry fruit [52,90]. Silicon’s primary function is by silica deposition in tissues, thereby strengthening plant tissue mechanical resistance [91]. It forms complexes with plant cell wall components, including hemicellulose, pectin and lignin, establishing covalent bonds to strengthen mechanical and structural properties towards improved plant resistance to biotic and abiotic stresses [92]. Si has been shown to be effective in suppressing diseases of fresh produce, including gummy stem blight of cucumber [93], powdery mildew plus two-spotted spider mite in strawberries [94], bacterial fruit blotch in melons [95], anthracnose in tomato [96] and capsicum [97], and Xanthomonas wilt in banana [98]. These findings support Si’s purported role in disease mitigation through postulated structural enhancements (e.g., thicker cuticle), and promoting suppressive secondary and primary metabolites (e.g., phenolics, peroxidase activity, sorbitol, fructose, maltose, cellobiose, malic acid, phosphoric acid and gluconic acid) [53,95,96].

The efficacy of Si is modulated by various factors, including its concentration and method of application. A dose-dependent effect was observed in various fresh produce lines, including raspberry. In this case, increasing the dose from 400 to 1600 mg L⁻¹ resulted in greater firmness [51]. The potentially negative effect of high dose (250 mg L⁻¹) was evidenced in pepper plants were low amino acids, reduced total chlorophyll and decreased stem diameter were recorded [56]. Foliar versus root application of Si may differentially affect plant growth and quality. Root application of Si under excess nitrate stress improved cucumber growth and photosynthesis, possibly by enhancing N assimilation and chlorophyll synthesis rather than forming a physical barrier [99]. Towards controlling anthracnose in capsicum, Si root treatment was comparatively more effective than foliar spray [97]. Spray application of Sican provide a physical barrier to entry of pathogens through the deposition on surfaces and/or may involve an osmotic effect [97]. In contrast, root application of Si to capsicum? induced systemic acquired resistance [97]. Holistically, Si may have multifaceted roles contributing to constitutive and induced resistance in plants. Further investigation is warranted to clarify the underlying mechanisms and requirements for the long-term efficacy of Si to enhance the quality and postharvest performance of leafy vegetables.

2.1.4. Other Macronutrients and Micronutrients

Besides the elements discussed above, potassium (K), phosphorus (P), and magnesium (Mg) are also important macronutrients reported to play key roles in fruit yield and quality as well as supporting plant response to adverse conditions [23,100]. Applications of P and K both improved the nutritional quality of baby spinach by increasing levels of total phenols, total antioxidant activity, flavonoids and vitamin C content [58]. Application of P increases biomass and lycopene content of tomato at 60 kg P ha⁻¹ [101]. Similarly, increasing K up to 300 mg·L⁻¹ in growing solution for hydroponic tomato enhanced its nutritional value by increasing levels of protein, ascorbic acid, lycopene, TSS, reducing sugars, and titratable acidity [57]. Mg has been reported to improve the yield and quality of tomato, including fresh weight, vitamin C, carotene and firmness, under controlled conditions in the field [60]. Likewise, optimised application of Mg improved apple quality by modulating photosynthetic N use efficiency, carbon-N metabolism, and anthocyanin biosynthesis [59]. However, in pepper fruit, whilst Mg improved yield, it reduced vitamin C [102], possibly by a dilution effect or otherwise unknown physiological or biochemical response, warranting further research [102].

Micronutrients have been reported to enhance reactive oxygen species (ROS) scavenging systems, including bioactive and antioxidant compounds with the potential to mitigate the effects of abiotic stress in plants [103]. For instance, iron significantly enhances nutritional and quality attributes of fresh produce by improving bioactive compounds (e.g., ascorbic acid, vitamins A and C, total polyphenol, flavonoid and anthocyanin), firmness and color [5,61]. Molybdenum (Mo) has been shown to promote crop productivity, along with nutritional content and general quality of fresh produce [62,63,104]. Boron has been associated with enhanced N, Ca and K uptake, as well as in improving fresh weight, marketable yields, shelf life and firmness [65]. It also positively influenced the crop physicochemical parameters of leaf area index, chlorophyll content, nitrate reductase activity, ascorbic acid and protein, but not starch content [64].

Manganese (Mn) plays critical and diverse functions in plant photosynthesis, respiration, scavenging of reactive oxygen species (ROS), pathogen defense and hormone signalling [105]. This is demonstrated in alleviation of oxidative stress-related blemishes in bell pepper by reducing H₂O₂, ascorbate oxidase and increasing apoplastic ascorbic acid. Yet, direct links between Mn and the mechanism by which it offers protection to the plant require further investigation [66]. A single spray of micronutrients such as copper (Cu), Mn and B at concentrations between 0.0025 and 0.02 M induced local and systemic protection against powdery mildew in cucumber plants [25]. Likewise, Zn has been reported to enhance microbial resistance, inhibit cell wall degradation and assist in maintaining cellular compartmentalization while also increasing phenolic and flavonoid levels, titratable acidity, TSS and anthocyanin content in fruits [69,106]. Such findings suggest important roles for micronutrients in enhancing the quality of fresh produce by modulating important physiological, biochemical and structural processes in plants. Further research is required towards integrating micronutrients into preharvest robustness strategies, including into crop-specific treatments, characterising interacting effects with environmental conditions and undertaking validation for sustainable application in practice.

2.1.5. Interaction of Mineral Nutrients

Nutrient interactions, either synergistic or antagonistic, play a significant role in plant physiological processes, influencing both yield and quality of horticultural crops [107]. In Chinese brassica an antagonistic effect of excessive ammonium limited Ca uptake and caused physiological dysfunction resulting in yield reduction [108]. Increasing N beyond plant needs may induce coupled N and Ca leaching, as increasing N makes the soil more acid, resulting in cations exchange, wherein H⁺ can displace Ca²⁺ thereby depleting soil Ca content [109]. Such nutrient interactions may lead to physiological disorders, like blossom-end rot in tomato. Low N:Ca has been associated with reduced disease incidence in avocado fruit [13] and reduced postharvest rot in Pak choi [74]. For mango fruit, maintaining a balanced N-to-Ca ratio is pivotal to achieving optimal fruit quality and minimizing physiological or internal disorders [14]. Also, application of an ammonium sulphate to calcium nitrate in a ratio of 70:30 proved beneficial in reducing fruit disorders, such as sunburn and fruit cracking, in pomegranate [110]. This ratio was associated with high marketable yield. In general, an optimized combination of N and Ca is considered to enhance fresh produce quality.

Single spray applications, but not mixtures of B, Cu and Mn were effective in inducing resistance in cucumber plants against powdery mildew [25]. Both synergistic and antagonistic interactions of these three nutrients were observed for apple fruit [111]. Combining B and Mn application increased the uptake of both elements compared to individual application, suggesting mutual facilitation due to the ionic interactions of the anion and cation. However, an antagonistic effect was observed between Cu and Mn, which may be due to competition for uptake.

Interactions between Ca and Si display both synergistic and antagonistic effects on fresh produce quality. Their combined application has been shown to increase aromatic compounds and amino acids in grape [112], enhance tolerance to fruit collapse in pineapple [113] and alleviate Ca deficiency in cabbage [114]. Si enhances root growth, supporting Ca uptake and mitigating Ca deficiencies [114,115]. However, plant response to Ca and Si may differ among plant species and cultivation conditions [116]. Moreover, application of calcium silicate to soil can increase soil pH, which may result in excess N and dilute Si in tissue through growth promotion [117]. Inconsistency in interactions of Si and Ca and its interaction with other nutrients merits further research to understand and optimize treatments.

Combinations of foliar Ca plus K were effective in enhancing peach color and firmness, as well as their uptake per se. Synergistic combinations have also been observed among other nutrients such as N and Mg [118] and Ca and Zn [119] in terms of photosynthesis, reduced ion leakage and fungal decay and increased bioactive compound levels, with all being associated with quality and sustained shelf life. Optimal combination of K and N significantly improved the quality, shelf life, and antioxidant levels in tomato [120]. Combined Ca and Zn treatment positively increased phenolic compounds and antioxidant enzyme activity while reducing polyphenol oxidase and fungal decay, suggesting that bioactive compounds prospectively mitigate injury in cold-stored grapes [119].

Balanced contents reflected in ratios of specific minerals are associated with fresh produce quality. In persimmon fruit, Ca, Mg [60] and indicative ratios of N to Ca (N:Ca) and Ca to K and Mg (Ca:(K + Mg)) were linked to positive quality traits, including color, firmness, TSS, and soluble tannin content [121]. Conversely, stem end rot and body rot incidence in ripe mango were positively linked to higher flesh and skin index mineral ratios of N:Ca, K:Ca, Mg:Ca, and K + Mg:Ca. These diseases were negatively correlated with Ca [13]. Thus, correlations among macronutrients like Ca and Mg with corresponding indicative ratios (e.g., N:Ca, Ca:[K + Mg]) constitute quality and robustness indices for fresh produce [121].

Ionics play a role in plant nutrient uptake in that, for example, increased anion uptake may stimulate cation absorption and vice versa [108]. This context is also relevant in the general context of robust fresh produce being able to withstand environmental and management stresses. Nonetheless, studies on plant–nutrient interaction tend to be inconclusive due to multiple interacting factors including crop type, nutrient dynamics, soil types and environmental variability [107]. This intricacy poses a challenge in formulating balanced nutrient management regimes in and across diverse production systems, hence the importance of mineral nutrition in regional research, development and extension activities attuned to specific crops under actual production conditions should not be underestimated. By integrating grower practice into participatory action trials in a soft systems context [122] can prospectively facilitate optimized nutrient management strategies [123]. Such farming systems approach can serve to verify and validate research under real-world agronomic conditions [123,124].

2.2. Role of Elicitors

Systemic acquired resistance (SAR) and induced systemic resistance (ISR) are primary defence responses in plants [125]. They differ primarily in the underlying signalling pathway that leads to similar phenotypic responses [126]. SAR relies on salicylate (salicylic acid, SA) and the accumulation of pathogenesis-related (PR) proteins [19]. By contrast, induced systemic resistance (ISR) relies on ethylene and jasmonate (jasmonic acid, JA) [19]. These plant defence mechanisms can be induced or elicited by various inducers, also called activators [127].

Elicitation is used to enhance the quality and robustness of horticultural and other crops. Elicitors trigger physiological and morphological defence responses in plants against biotic and abiotic stresses [128]. Responses involve the production of secondary metabolites that include flavonoids, anthocyanins, lignins, tannins, phenolics, and antioxidants that underpin resistance and enhance fresh produce quality, including robustness [129,130]. Secondary metabolites do not play a direct role in the primary metabolism of plants. However, they are important in their interaction with the environment, including in enhancing plant survival, adaptation and competitiveness [131]. Elicitors may modulate changes in genes involved in primary and secondary metabolism, including ion homeostasis and plant hormone pathways aligned with defense system responses [132].

Elicitors are generally classified as biotic or abiotic and exogenous or endogenous [131]. Abiotic elicitors that have a significant impact on plant resistance include auxins, cytokinins, gibberellins, abscisic acid (ABA), and ethylene (ET) as along with brassinosteroids, jasmonic acid, salicylic acid, and small peptides [133,134,135]. Physical elicitors include irradiation with ultraviolet (UV) light in the bandwidths UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm) along with other wavelengths of the electromagnetic spectrum. In practice, light-emitting diodes (LEDs) [136,137] have been used to induce resistance and improve fresh produce quality. Elicitors have been demonstrably effective in alleviating various plant stresses, with inherent potential for enhancing robustness and otherwise improving fresh produce quality at harvest. Positive effects for disease resistance and their roles in promoting physicochemical, bioactive, and nutritional quality of fruits and vegetables are summarised in

Table 2. Effects of various elicitors on the physicochemical, bioactive, and nutritional quality of fruits and vegetables relating to pathogen resistance and enhanced fresh produce qualities, including longer shelf life, higher fresh weight, and increased promotive chemical constituents.

Elicitor	Disease and Physicochemical Quality	Bioactive and Nutritional Quality	Produce	References
Salicylic acid/methyl salicylate (MeSa)	Disease resistance against black mold disease, yellow leaf curl virus, Fusarium wilt, Delayed ripening and senescence, prolonged shelf life, reduced fresh weight loss, improved firmness, colour, and acidity, maintained chlorophyll levels, titratable acidity	Increased ascorbic acid, antioxidant capacity, glutathione, total phenolic, total flavonoid, anthocyanins, total chlorophyll content	Orange, grape, banana cherry, peach, wax apple, grape, peach, pepper, tomato, pointed gourd, Chinese chives, Brassica rapa	[138,139,140,141,142,143,144,145,146]
Jasmonic acid or methyl jasmonate (MeJa)	Disease resistance against Alternaria alternata, Rhizopus stolonifera, stem end rot anthracnose rot Improved colour, total soluble and sugar content alleviating chilling injury reducing pericarp browning	Increased phenolics, flavonoids, total chlorophyll, phenols and flavonoids, vitamin C, volatile components	Sweet cherry, peach, mango, pear, prune, longan, lychee, tomato, bell pepper broccoli florets, kale leaf, lettuce	[147,148,149,150,151,152,153,154,155,156,157,158,159]
Irradiation UV-B, UV-C, UV-A, LEDs, gamma, far-red, red and blue light	Disease resistance against powdery mildew, Penicillium digitatum, Xanthomonas campestris Retained firmness, delayed ripening, increased growth, reduced chilling injury, electrolyte leakage, respiration, improved biomass, thicker and more compact leaves	Increased carotenoids, anthocyanins, flavonoids, glucosinolate, phenolic compounds, vitamin C content, antioxidant capacity	Strawberry, blueberry, eggplant, tomato, lettuce, kale, broccoli microgreens, brassica sprouts	[160,161,162,163,164,165,166,167,168,169,170,171]

.

2.2.1. Elicitors

Robust fresh produce may be achieved through the application of elicitors (Table 2). Among them, SA has been widely studied against a spectrum of plant pathogens. Elicitors work through the activation of defence-related genes active in SAR, which can provide sound and long-lasting immunity in plants [172]. On the other hand, MeJa induces gene expression and activity for antioxidants and defence enzymes by activating phenylpropanoid and jasmonate pathways of resistance [147,148,173]. Moreover, defence can be elicited by physical means such as irradiation via direct oxidative stress or indirect photoreceptor perception [174,175].

Salicylic acid treatments can mitigate reactive oxygen species (ROS) accumulation by enhancing antioxidant activity, which in turn can positively impact fresh produce quality [176]. Jasmonates too have regulatory implications for quality [177]. Jasmonic acid is involved in modulating membrane lipid metabolism, maintaining cellular energy balance, regulating ROS homeostasis, and enhancing antioxidant capacity [152,154]. Irradiation treatment approaches can similarly positively affect fresh produce quality such as in leafy vegetables.; UV-A and UV-C exposure elicited positive effects in improving growth and quality of Chinese kale and spinach, respectively [136,178]. Moreover, UV-C has been shown to enhance resistance in lettuce against bacterial leaf spot and reduce microbial contamination in baby leaf spinach [136,179].

Elicitors can also enhance nutritionally bioactive compounds that not only contribute to robustness and overall quality of fresh produce but also elicit more nutritious food to meet consumer needs and general well-being (Table 2). SA enhances nutritional quality by sustaining the ascorbate-glutathione cycle, promoting synthesis of ascorbic acid and glutathione (GSH), inhibiting degradation of flavonoids, total phenols, and anthocyanins, and increasing antioxidant enzyme activities for free radical scavenging capacity [176,180]. Similarly, JA mediation of antioxidant enzyme activities can enhance accumulation of phenolics, flavonoids, and carotenoids contributing to improved nutritional and functional quality in different fresh produce. Irradiation activates genes involved in the phenylpropanoid pathway that are associated with the production of bioactive compounds and enhanced nutritional quality [181]. This includes the production of compounds with health benefits, such as lutein and phenolic compounds in kale [170] and antioxidants in Brassica sprouts [170].

Thigmomorphogenesis can be employed as a preharvest strategy to elicit innate stress responses and improve the quality and robustness of fresh produce. This approach involves mechanical stress stimulation that induces physiological, developmental, anatomical, and morphological responses reflecting plant responses to biotic disease and abiotic mechanical stress [182,183,184]. Physical perturbation can be through wind, touching, or flexing as well as artificial external mechanical stimulation [182]. For instance, rubbing the fourth internode in tomato plants elicited a growth response characterized by lignification and cell wall rigidification [185]. Likewise, touch stress induced hardening, evidenced by increased lignin content, reduced elongation and increased diameter growth in papaya seedlings [186]. In bean plants, exposure to wind decreased stem elongation and increased radial enlargement [187]. Thus, thigmomorphogenesis can result in more sturdy plants equipped to withstand various stresses. However, studies on fruit and vegetables are limited, especially with leafy vegetables. Further research is evidently warranted into thigmomorphogenesis relating to the physicochemical quality of fresh produce.

2.2.2. Crosstalk Interaction of Elicitors

Plants are often subjected to multiple environmental stresses. Hence, they need to respond in situ to varying and often adverse conditions that negatively impact growth, yield, and overall plant health [188]. The interaction of elicitors, including hormones (plant growth regulators) and other messaging agents, plays a pivotal role in mediating robustness under multiple stresses. Crosstalk among hormone signalling pathways, such as SA, JA and ET-mediated pathway, coordinates defence. The interactions can be synergistic, antagonistic, or additive in influencing gene expression, protein production, and plant homeostasis [189]. Interplay between SA, JA, and ET establishes the defence strategy. In response to biotrophic pathogens or herbivorous insects, SA- and JA/ABA-dependent defence mechanisms are triggered. The JA/ET pathways modulate susceptibility to necrotrophic pathogens [190].

Studies have also demonstrated synergistic effects of different elicitors on quality, endogenous bioactives, and general nutritional value of fresh produce [191,192,193,194]. For instance, a combination of JA (1 μM) with other elicitors, including hydrogen peroxide (27 mM) and chitosan (0.75% ^w/_v) improved bioactive compounds and antioxidant activity in sweet bell pepper [192]. Similarly, combined applications of SA with other elicitor treatments including calcium carbide, chitosan, and blue light exposure enhanced antioxidant bioactive compounds, shelf life, and resistance to decay in blackberry, strawberry and phalsa fruits [195,196,197]. Such combined applications also result in delayed water loss and preserved sensory and nutritional quality in fresh produce [195,196,197]. The interacting effects of elicitors attest to the importance of understanding their intricate crosstalk and applied impact on fresh produce quality. However, ‘costs’ are associated with elicitation they being variously termed ‘metabolic fitness’, ‘growth-defense trade-off’ or ‘allocation’ costs’ [198,199]. Metabolic redirection can prospectively compromise yield and quality and potentially dampen priming, thereby limiting efficacy against postharvest stresses. By optimizing defense priming through technologies such as use of nanoparticles and genetic engineering of signaling pathways may be possible to enhance defence mechanisms to favour robust, high-quality fresh produce while minimizing any fitness costs of energy consumption.

2.2.3. Factors Affecting Elicitor Efficacy

The efficacy of elicitors in enhancing the quality and robustness of fresh produce is influenced by factors such as concentration, duration, and timing of application and prevailing environmental conditions. For example, a dose-dependent effect of salicylic acid (SA) was observed in lettuce under salt stress [200]. With strawberry, optimal levels of MeJa and SA preserved firmness, while higher doses of both of these elicitors, also enhanced ascorbic acid and bioactive compounds during storage. MeJa proved to be the more effective of the two bioactives when considering inhibiting fungal growth [201]. Preharvest treatment with 500 μM MeJA and 150 μM SA improved growth, antioxidant activity and flavor in Chinese chives [202].

Considering irradiation, short-term (6 h) UV-B treatment did not affect growth of microgreens while it enhanced their nutritional benefits [203]. Low dose UV-C (1.5 kJ m⁻² enhanced antioxidant capacity and reduced microbial counts on spinach leaves. However, this treatment was ineffective in reducing mold counts in the field and could potentially adversely affect plant development over time [136]. Longterm UV-B treatment improved ripening and anthocyanin content in blueberry in a fruit maturation stage-related manner. In tomato, the highest of UV-C dose maintained the fruit firmness in a dose–dependent effect [163]. With factors mediating elicitor effects, it is important to optimize promising treatments. In particular, concentration, duration, and timing of treatment must be considered. Nevertheless, it remains a challenge to identify effective treatments as efficacy is modulated by interacting environment and genetic factors [175]. Hence, to realize the benefits from elicitors to enhance fresh produce robustness, it is important to consider and characterize preharvest interacting factors in well managed production systems.

3. Measuring and Monitoring Fresh Produce Robustness

Measuring and monitoring are important for assuring quality and validating the efficacy of measures applied to supply robust fresh produce. Advanced technologies, including spectroscopy, imaging and image analysis, are increasingly used in fresh produce quality management as non-destructive rapid means of assessment [204]. Real-time monitoring by supply chain stakeholders from production to consumption can help ensure that fresh produce meets market and consumer needs.

Optical spectroscopy has been used widely for nondestructive rapid assessment of food quality, with many examples of using visible–near-infrared (Vis/NIR) and near-infrared (NIR) spectroscopies being applied [204]. The visible absorption spectrum primarily conveys information on pigment colors. The non-visible NIR spectrum relates more to structural composition, including of organic molecules with C–H, N–H and O–H bonds [205]. The data are conventionally analyzed using multivariate chemometric statistical methods, including partial least squares (PLS), principal component regression (PCR) and principal component analysis (PCA) [206,207,208]. However, deep learning-based machine learning approaches have been increasingly utilized to model spectral data obtained from analytical experiments, enhancing the veracity of measurement [209]. Before the application of spectroscopic methodologies in the field, the use of objective measurements for physical and chemical qualities necessitated numerous replications to ensure the accuracy and applicability of the technology under field conditions. Calibration of chemometric or machine learning models involves the acquisition of spectral data from reference samples of known attributes. Thereupon, predictive models are produced that quantitatively correlate spectral responses with specific attributes [210].

NIR technology is widely used to predict fresh produce quality. However, poor prediction accuracy for texture or firmness has been reported in stone fruit, particularly apricots, nectarines, peaches, and plums [211,212]. This limitation relates to physical characteristics not directly linked to the absorption spectra of chemical molecules [212]. Other factors that also contribute to inconsistent results include changes in physicochemical properties and their changes. These include, for example, cell water content changes and factors such as pest or pathogen infestations, high light exposure, sunburn, and postharvest handling and treatments, including ripening protocols [211]. Moreover, genotypic variability can differentially influence results. For instance, soluble solids in ‘Golden May’ apricots were less accurately discerned compared to other stone fruits [211]. Moreover, the analyses and models also impact variability in the prediction of quality. While different machine learning tools, such as support vector regression (SVR), and k-nearest neighbors (kNN) have demonstrated high predictability of the quality measured by the models, they are typically specific to the calibration dataset [213].

Improvement in spectral approaches, including integrating NIR or VisNIR with hyperspectral imaging (HSI), has improved the utility of NIR for monitoring and measuring quality. This addresses various limitations of NIR, such as no spatial distribution of the quality attributes, and expands applicability in horticulture [214]. While HSI can provide more details of both spatial and spectral information, it exceeds the capacity of NIR for analyzing heterogeneous samples [215,216]. The visible to near-infrared range from 400 to 1000 nm in hyperspectral imaging enabled bruise severity detection in pomegranate fruit [217], detection of firmness and soluble solids in pear fruit [218], and prediction of freshness with storage duration [219,220,221,222]. Different features of visible/near-infrared (NIR), NIR hyperspectral imaging and hyperspectral imaging, including their application in determining the quality of fresh produce, are shown in

Table 3. Application of Vis/NIR spectroscopy, NIR hyperspectral, and hyperspectral imaging as non-destructive measurement technologies towards ensuring quality and robustness in fruits and vegetables.

Feature	Visible/Near-Infrared (vis/NIR)	Near-Infrared Hyperspectral Imaging	Hyperspectral Imaging
Spectral acquisition	Spectral data invisible region (380–780 nm) and near-infrared region (780–2500 nm), spot-scan measurement	Spectral data with imaging, both spectral and spatial information across the NIR region, 1100 to 2500 nm	Spatial and spectral data across a broader wavelength range 1000 nm to 2500 nm, in line and area scan techniques
Data information	One-dimensional spectral data for each point/sample, chemical quality such as sugar, moisture, and acidity	Hyperspectral data cube, two-dimensional geometric space and one-dimensional spectral information, distribution of physicochemical properties	Hyperspectral data cube, two-dimensional geometric space and one-dimensional spectral information (hundreds of bands of continuous wavelengths) for extensive data on physicochemical qualities
Fresh produce	Orange, mandarin, grape,	Strawberry, kiwi, citrus, pomelo	Apple, spinach, and Chinese cabbage, leafy vegetables
Quality	SSC, color, content, color, firmness, pH, flavanols, TPC, vitamin C, and antioxidant activity	Prediction of storage time, textural profile analysis, SSC, vitamin C and organic acid contents	Early bruise detection, diseases N, P, K deficiency, freshness quality
Cost	Less expensive, less complex setup, less computationally demanding.	Moderate cost, but becomes more expensive with higher wavelengths up to 2500 nm	Expensive setup, including advanced computing to process large datasets
References	[205,207,212,213,216,223,224,225,226,227,228]	[205,214,217,219,223,229,230,231]	[207,216,217,220,221,222,232]

.

Several factors limit the use of near-infrared hyperspectral imaging. They include cost, variability in quality prediction, varying genotypic and phenotypic characteristics of samples, and environmental conditions. High system cost is due to specialized equipment, especially for extended wavelength ranges up to 2500 nm, sophisticated spectrometers and high-definition cameras, and to the requirement for an advanced computer with high speed and large storage capacity for complex data analysis [214,223,233]. Detection of wavelengths beyond 1100–2500 nm requires more costly indium gallium arsenide (InGaAs) or mercury cadmium telluride (HgCdTe) based array detectors, whereas less expensive silicon-based detectors are used for wavelengths up to 1100 nm [223]. By contrast, light detectors and cameras are relatively inexpensive in the visible region, as they are based on silicon. After about 800–1000 nm, silicon is not efficient, and more expensive semiconductors, such as GaAs (gallium arsenide), are used (D. Pelliccia, pers. comm.).

Additionally, the accuracy of NIR and HSI models is also affected by factors including environmental and genotypic variability. Single-cultivar models have smaller prediction errors than multi-cultivar models due to their higher specificity providing improved accuracy but lesser applicability across multi-cultivar datasets [234]. A multi-cultivar model was found to be superior to individual-cultivar models for soluble solids content (SSC) prediction by using effective variables. However, to optimize the model necessitates including extensive and diverse samples [235]. Moreover, data and robustness are influenced by environmental variables like temperature and humidity that are not consistently addressed in calibration models [175].

To overcome this limitation, a holistic approach can be developed, especially in prioritizing cost-effective approaches, increasing the size and diversity of datasets used for calibration. This consideration includes standardizing calibration models that consider multi-variety applications and environmental factors such as temperature and humidity to enhance model robustness and applicability across diverse conditions [175,194]. Advanced machine learning models that adapt to cultivar-specific traits and environmental factors can improve prediction accuracy for diverse produce types, ensuring reliable grading and sorting systems [194,196]. Enlarging datasets, including pooling together different sources of data, can help towards making the spectroscopy system more widely applicable (D. Pelliccia, pers. comm.).

The development of handheld or portable spectroscopy addresses the limitation of in-field NIR application, obviating large benchtop NIR units and lowering costs, as well as offering faster, more direct quality monitoring [236]. However, limitations of portable devices include limited wavelengths and signal-to-noise ratio. Extending spectral ranges and improving device-specific calibration protocols can improve accuracy for parameters like TSS and acidity [195]. Using an optimized model, portable NIR spectroscopy predicted the quality of injured peaches [237], maturity in avocado [238], SSC, pH, and TA in plum [239], SSC, titratable acidity, pulp firmness, and starch-iodine index in apples [236], dry matter content (DMC) and SSC in kiwifruit [240], firmness, SSC, pH in cherry tomato [241], and SSC and DMC in mango [242].

Notably, handheld NIR has been paired with smartphones, offering a more user-friendly and real-time application and interpretation, as demonstrated in predicting TSS and pH in mango [243], soluble solids content, titratable acidity, pulp firmness, and starch-iodine index in apple [236]. NIR output interfaced with smartphone technology permits the software application (App) to transmit, plot, and analyze spectral data [244]. The App interface can be linked to cloud computing data processing software for faster analysis of data for quality parameters. Most improvements are related to being able to increase the size and diversity of the data sets used for calibration. An issue in many studies reporting the use of spectroscopy in produce is small datasets (D. Pelliccia, pers comm.); hence, models that work on limited datasets do not generalize either to future data or to different equipment. Enlarging datasets and pooling together different data sources could make this spectroscopy system more widely applicable for quality parameters such as lycopene content in tomato [245] or harvest maturity and TSS of sweet cherries [246]. Advanced systems combining portable NIR spectroscopy with cloud-based computing and smartphone technology are actively researched, developed, and applied. They enable broader application of rapid, real-time and nondestructive monitoring of fresh produce quality from production through the supply chains.

In the contexts of ‘Section 2.1. Plant nutrient management’ and ‘Section 3. Measuring and monitoring fresh produce robustness’, cloud-based applications that can measure and report plant tissue (e.g., leaf) nutrient contents are in the offing, for example, a Picketa Systems LENS™ decision support platform (https://www.picketa.com/) (accessed on 9 January 2025).

4. Challenges and Recommendations

The quality of fresh produce is influenced by complex and interactive factors during production, including genetics, environmental conditions and management decisions as well as by unforeseen challenges (e.g., delays) along the supply chain. These myriad factors pose challenges in optimizing preharvest strategies to meet the growing demands for high-quality, resilient fresh produce. Nutrient management is a keystone preharvest strategy, with N playing a primary role in enhancing productivity and yield of fresh produce. Overuse of N, however, often undermines the sustainability of farming systems. By way of example, this necessitates precise, crop-specific strategies to optimize N source, timing, and application levels, particularly in leafy vegetables and microgreens. Similarly, other essential nutrients like Ca contribute to improving produce quality. However, their dynamic interactions with other nutrients are also affected by different preharvest factors, such as the timing of application, concentration of each nutrient and environmental conditions. Controlled environment studies offer insights into nutrient management. However, long-term and field-based research is important for verifying and validating the practicality and reliability of such strategies, including under actual farming conditions.

Despite the demonstrable benefits of elicitors in enhancing plant immunity along with increased production of bioactive compounds and improved nutritional and physicochemical quality of produce, inconsistent findings represent challenges. For example, fitness costs can compromise yield and quality and reduce efficacy against postharvest stresses. While elicitors may not fully replace synthetic pesticides, their use in a multi-barrier strategy may enable reduced pesticide application levels, providing safer, more sustainable agricultural practices. While the strategic use of nutrients and elicitors may enhance the resilience of crops against biotic and abiotic stresses, studies on the interaction between elicitors and nutrients are limited. For instance, crosstalk between MeJa and Ca, which regulates the production of specific metabolites, was studied in cultured grape cells, but its direct impact on fresh produce quality was not evaluated [247]. Moreover, the application of N fertilizers with elicitors such as PGPR (plant growth-promoting rhizobacteria) and SA sprays has been shown to improve quality and yield [248]. Several studies also reported the synergistic relationship of Si and salicylic acid, leading to improved physiological processes and enhanced stress tolerance of plants [249]. Despite these promising findings, the potential for integrating nutrient and elicitor treatments needs further evaluation, especially in producing robust fresh produce.

The integration of NIR and HSI methods in fresh produce quality assessment has shown significant potential for measuring quality in more depth, addressing the limitations of NIR when used in isolation. The incorporation of HSI entails higher costs, which is a limitation in the application of this technology. Nevertheless, the development of portable handheld NIR/HSI devices is a promising approach for in-field applications and for reducing the cost of sophisticated spectral systems in the laboratory. Yet currently it is often restricted by limited wavelength ranges, resulting in lower-quality predictions compared to laboratory-based systems [195]. However, integration with cloud-based computing through advanced machine learning and smartphone applications can enhance accuracy and improve accessibility by allowing real-time data analysis and remote storage while providing a user-friendly mobile interface. This technological integration increases the broader application of NIR/HSI, enabling precise, scalable, and non-destructive assessment of robust fresh produce.

5. Conclusions

Quality at harvest is crucial to ensure a sustainable supply chain that can meet consumers’ needs, expectations and well-being. Only robust fresh produce at harvest would be sufficiently resilient to withstand the range of often unavoidable biotic and abiotic stress conditions imposed on fresh fruit and vegetables from preharvest to postharvest handling. To maximize fresh produce robustness, effective optimization of preharvest strategies is essential, considering that quality is governed by interacting preharvest factors across varying genotypes, environmental conditions, and crop management practices. Plant nutrient management, including N, Ca and Si, plays a pivotal role in plant growth and development and also in stress tolerance towards robust produce. Appropriate and balanced nutrient application involves optimizing sources, application methods, timing, and interactions among nutrients to prevent excess or deficiency that can compromise quality. On the other hand, elicitors, including SA, MeJa and managed stress through electromagnetic irradiation have shown promise towards enhancing plant resilience and robustness quality via inducing plant innate immunity against biotic and abiotic stresses. Such approaches can enhance disease resistance, improve physicochemical properties, and increase bioactive compounds and nutritional quality.

However, further investigations qualifying and quantifying different production factors and variables on the practical efficacy of elicitors are required to realize their prospective benefits, including in-field studies. Integrating nutrient management and elicitors offers a more holistic approach to address the limitations of individual strategies to optimize fresh produce robustness under complex preharvest conditions. Moreover, postharvest management, particularly monitoring quality using near-infrared and hyperspectral analysis, including imaging, in the supply chain represents an enabling synergy for producing assuredly high-quality, robust fresh produce.