In We have a lot at stake in modern agriculture.To produce quality food, reduce losses, and do so in a way that respects the environment and people's health, while promoting natural adaptation to droughtThe problem is that traditional chemical tools are increasingly limited, generate resistance in pathogens, and, moreover, do not fit with the new demands of sustainability.
In this context, Natural elicitors have become one of the great assets to manage pests, diseases, and stress without relying so heavily on synthetic pesticides. Instead of directly killing the pathogen, these compounds "train" the plant, activating its defense system and preparing it to respond better to fungi, bacteria, viruses, insects, or abiotic factors such as drought, cold, or salinity.
What are natural elicitors and why are they so interesting?
When we talk about elicitors, we are referring to molecules capable of triggering the internal defenses of plantsThey can be derived from plant extracts, fungi, bacteria, cell walls, secondary metabolites, phytohormones, or even inorganic compounds and physical stimuli. They are not conventional fertilizers or fungicides, although some exist. natural fungicides employed in seedbeds and ecological management.
In cases they act as intermediaries in plant-pathogen recognitionThey bind to specific receptors on the plasma membrane and, from there, trigger a signaling cascade that affects the expression of hundreds of genes related to defense. The result is a state of “immune alert” that often extends beyond the initial point of application.
According to their origin, elicitors are usually classified into endogenous and exogenousEndogenous compounds are fragments or molecules generated within the plant itself, such as cell wall fragments released after damage or stress. Exogenous compounds originate from pathogens (fragments of fungi, bacteria, viruses), beneficial microorganisms, botanical extracts, or chemical substances applied from the outside.
Another commonly used criterion is its nature: biotic and abiotic elicitorsBiotic factors include complex carbohydrates in cell walls, oligosaccharides, proteins, enzymes, and fatty acids such as arachidonic acid. Abiotic factors encompass metallic salts, UV radiation, low temperatures, inorganic compounds such as sodium silicate, and gases such as ozone and CO₂.2 and even physical treatments such as heat or pulsed light.
The important thing is that, after the action of an elicitor, the plant enters a state of Acquired systemic resistance (SAR) or induced systemic resistance (ISR)In this state, the defensive mechanisms are activated or "pre-charged," so that when the actual pathogen arrives, the response is faster, more intense, and more effective, even in organs that were not directly treated.
How induced immunity works: SAR, ISR, and key hormonal pathways
Plant defenses are organized into two main levels: preformed (constitutive) defenses and induced defensesThe preformed ones are those physical and chemical barriers that already come "standard": waxy cuticle, thickness of the epidermis, trichomes, cuticle composition, characteristics of stomata and lenticels, or the presence of substances such as terpenes, alkaloids, phenols or saponins.
The induced defenses are only activated when the plant detects an attack or a stress stimulus. At that moment, the so-called hypersensitive reaction (HR), a localized cell death at the point of infection, driven by rapid changes in ion flow, phosphorylations/dephosphorylations and a strong production of reactive oxygen species (ROS) such as H2O2 and superoxide radical, along with an increase in nitric oxide (NO).
This reaction limits the advance of the pathogen and is accompanied by the synthesis of Phytoalexins and other defensive metabolitesThese include phenols, lignin, tannins, flavonoids, glucosinolates, glucanases, chitinases, lectins, terpenes, alkaloids, and saponins, among others. In insect-resistant plants, compounds that interfere with pest growth and fertility also accumulate.
Elicitors take advantage of precisely this system: They simulate the presence of an attack without the pathogen actually causing damage.In this way, the plant activates its defense mechanisms in advance and reduces its future vulnerability. Therefore, it is recommended that the inducing treatment be applied before the pathogen arrives and followed tips to avoid pest attacknot when the disease is already fully established.
Phytohormones play a fundamental role in this entire process. The two most studied pathways are those of salicylic acid (SA) and jasmonic acid (JA)These are joined by ethylene and, in situations of abiotic stress, abscisic acid (ABA). AS is closely linked to SAR, especially against biotrophic pathogens; AJ and ethylene are more associated with defense against necrotrophic pathogens and herbivores.
The balance between both paths is critical: Excessive AS signaling can make the plant more vulnerable to insectsWhile overactivation of the AJ can reduce resistance to certain pathogens and penalize growth, as resources are diverted towards defense rather than biomass production.
That is why new generation commercial products, especially those of natural origin, are formulated to modulate the AS, AJ and ethylene pathways in a balanced wayseeking global protection without hindering the vigor or productivity of the crop.
Complexity in the use of elicitors: dose, mixture and environment
Using elicitors is not as simple as applying a contact fungicide and forgetting about it. For them to work properly, certain precautions are essential. adjust the dose and application time correctlyDoses that are too low may not activate defenses sufficiently, and doses that are too high may cause a disproportionate response that compromises growth or causes phytotoxicity.
We must also consider their compatibility with other products in the management programSome elicitors can lose effectiveness if mixed with certain pesticides or fertilizers, or conversely, they can interfere with the action of other treatments. Checking labels, conducting preliminary tests, and seeking technical advice are key to avoid pests on plants and maximize effectiveness.
The Environmental conditions at the time of treatment have a significant influenceTemperature, relative humidity, solar radiation, and crop water status affect absorption, translocation, and physiological response. The same product can yield excellent results in one context and mediocre results in another if these variables are not taken into account.
Follow-up is equally important. Ideally, the use of elicitors should be accompanied by good monitoring. visual monitoring and, where possible, laboratory analysis to check for changes in defensive metabolites, antioxidant enzymes, or quality parameters. This makes it easier to adjust dosage, frequency, and combination with other management practices.
It's important to remember that elicitors are not a magic wand: In situations of intense stress or inadequate management, natural defenses declineExcessive synthetic agrochemicals, sudden changes in temperature and humidity, extreme radiation, or severe drought can overwhelm the capacity of the plant immune system and reduce the effectiveness of any resistance induction strategy.
Natural elicitors in pre- and post-harvest: quality improvement and preservation
Beyond direct disease control during the crop cycle, elicitors have proven to be very interesting tools for increase the content of phytochemical compounds and improve post-harvest preservationNumerous scientific studies have examined its effect both when applied in the field and directly on already harvested fruit.
In cherry, for example, the pre-harvest use of oxalic acid (OA) in varieties such as 'Sweet Heart' and 'Sweet Late'Applied at different concentrations (0,5, 1 and 2 mM) at key moments of fruit development (stone hardening, beginning of color change and beginning of ripening), the AO increased the size, volume and weight of the cherries, as well as improving color and firmness, with 2 mM being the most effective dose.
This type of treatment also resulted in a increased content of bioactive compounds and antioxidant potential At harvest time, the fruit has higher levels of anthocyanins, flavonoids, and chlorogenic acid derivatives. Many of these compounds are directly related to the fruit's visual appeal and health benefits for the consumer.
In plums of varieties such as 'Black Splendor' and 'Royal Rosa', oxalic acid and other natural elicitors such as methyl jasmonate (JaMe), salicylic acid (AS), acetylsalicylic acid (AAS) and methyl salicylate (SaMe) They have also shown very positive results. They were applied at various stages of development and at different concentrations, subsequently selecting the most effective one for quality and phytochemical analyses.
These studies observed a increased production and improved quality parameters (weight, firmness, color, soluble solids, and total acidity) both at harvest and after long periods of cold storage. In addition, higher levels of total phenols, anthocyanins, carotenoids, and ascorbic acid were maintained, along with greater activities of antioxidant enzymes such as peroxidase (POX), catalase (CAT), and ascorbate peroxidase (APX).
In artichokes, the pre-harvest application of AO and JaMe in the 'Blanca de Tudela' variety had similar effects: higher percentage of first-class headsIncreased total antioxidant activity and higher content of hydroxycinnamic acids and luteolins were observed both at harvest and during cold storage. A specific compound, luteolin 7-O-glucuronide 3-O-glucoside, was even identified for the first time in artichokes.
Methyl jasmonate, in particular, showed interesting behavior: The lowest concentrations (0,5 mM) helped to slow ripening and weight loss In post-harvest handling of plums, doses of 2 mM reduced ethylene production and respiration, while doses of 2 mM accelerated the ripening process. This demonstrates that the dose influences not only the intensity of the defensive response but also the ripening physiology.
Pre-harvest treatments with AS, AAS and SaMe in plum trees also improved quality: greater firmness, greater weight and higher concentration of organic acids and sugarsas well as phenols and anthocyanins (such as cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside) and carotenoids. During storage, these treated fruits retained their color, acidity, and bioactive compounds better.
Post-harvest elicitors to reduce losses and chemical waste
One of the major concerns today is that Nearly half of the world's fruit and vegetable production is lost post-harvest.Fungi are the main cause of these losses. Synthetic fungicides have traditionally been used to control diseases during storage, but overuse of these products leads to resistance, residues in food, and environmental problems.
Biological elicitors have gained prominence as harmless strategy to activate the fruit's defense system after harvestWhen applied in immersion treatments, coatings, nebulization, or modified atmospheres, they can trigger the synthesis of antimicrobial and antioxidant secondary metabolites, reducing the incidence of diseases and extending shelf life; many of these alternatives are included in compilations on traditional remedies complementary.
Among the induced metabolites, the following stand out: phenolic compounds, flavonoids, lignin and phytoalexinsThese enzymes strengthen the cell wall structure, limit pathogen penetration, and improve overall antioxidant capacity. Simultaneously, the activity of key enzymes such as phenylalanine ammonia lyase, superoxide dismutase, peroxidase, and polyphenol oxidase is increased, slowing lipid peroxidation of membranes and the oxidative stress associated with infection.
Fruits detect pathogens through recognition receptors in the plasma membraneThese processes trigger the production of ROS, the activation of G proteins, ubiquitin, kinases, calcium signaling, and a complex network of hormones and transcription factors. All of this converges on the regulation of defense genes, many of which have been identified thanks to omics technologies.
Transcriptomic and metabolomic studies in avocado treated with chitosan as an elicitor They showed the activation of multiple metabolic pathways: stress response, signal transduction, phenylpropanoid biosynthesis, and an increase in secondary metabolites involved in resistance to Colletotrichum gloeosporioides. Similar studies in mandarin treated with cyclic lipopeptides from Bacillus subtilis showed a greater accumulation of bioactive compounds.
Various elicitors have been tested in other fruits: Oligochitosan, salicylic acid, and the yeast Pichia membranaefaciens They have been shown to induce the phenylpropanoid pathway, responsible for the biosynthesis of structural polymers and protective pigments. Antagonistic yeasts such as Pichia guillermondi or Kloeckera apiculata, applied to plums, have successfully controlled Monilinia fructicola, while simultaneously activating the production of lignin, flavonoids, and phenols.
The biological control agents of the genus Bacillus also plays a prominent roleStrains such as Bacillus atrophaeus TE7 have achieved biocontrol efficacies exceeding 85% in mango against Cladosporium cladosporioides, while Bacillus subtilis ABS-S14, through its cyclic lipopeptides, effectively controls green mold in mandarin and triggers the expression of genes related to SAR, ROS, and Ca2+ and ABA.
In addition to organic compounds, the following have been evaluated: natural polysaccharides such as chitosan, fructooligosaccharides, carrageenans, fucans or agave fructansAll of these have shown good results in controlling diseases such as anthracnose in avocado. Other metabolites such as epicatechin, quercetin, essential oils, and antimicrobial peptides (mytichitin-CB, epsilon-poly-L-lysine) have shown efficacy in cherry tomatoes, apples, and strawberries.
The inorganic elicitors and exogenous gases Nor are they far behind: silicon, sodium carbonate, CO2Ozone or nitrous oxide have been shown to improve the stress and disease response in mandarins, grapes, jujubes, melons, and other fruits. In the case of CO22For example, it has been shown to activate genes associated with abiotic stress and reduce the expression of enzymes that degrade the cell wall, lengthening the firmness and shelf life of the fruit.
At a physiological level, many of these treatments induce profound changes in energy and oxidative metabolismProteomic studies in mitochondria of treated fruits reveal alterations in metal-binding proteins, ATPases, oxidoreductases and enzymes of glycolytic and tricarboxylic acid cycles, forming interaction networks that reinforce resistance while maintaining energy balance.
Elicitors in turfgrass and intensive crops: phosphites and key hormones
The use of elicitors is not limited to fruit trees or vegetables. It has also been observed that they are effective in sports and ornamental turf. The proper functioning of natural defense systems is crucial. to withstand attacks from fungi, bacteria, viruses, nematodes and, at the same time, cope with abiotic factors such as frost, drought, salinity or extreme heat.
In these grassland systems, defenses act on two levels: one active response based on physical and chemical barriers (cuticle, cell wall, terpenes, alkaloids, phenols, etc.) and a passive response linked to Local and Systemic Resistance. Elicitors, produced by the plant itself in response to stress or applied externally, trigger these responses.
One of the best-known elicitors in lawns is the phosphite (HPO)3-2)Famous for stimulating the formation of phytoalexins related to terpenes, alkaloids, and phenols, it has a particularly notable effect against oomycete fungi such as Phytophthora and Pythium. Its use has become established as part of smart management strategies to reduce dependence on conventional fungicides.
In the last decade, the following have also been identified other molecules with elicitor function in grassessuch as salicylic acid, jasmonic acid, ethylene, and abscisic acid. These hormones regulate the expression of genes for pathogenesis-related (PR) proteins, which are involved in protection against fungi, bacteria, viruses, and even nematodes.
The first level of stress response in turfgrass is local, related to the synthesis of phytoalexins from the enzyme phenylalanine ammonia lyase (PAL)The increase in PAL is linked to greater overall resistance. The second, systemic level involves the activation of PR genes distributed throughout the plant, largely mediated by salicylic acid, as described in numerous physiological studies.
Under conditions of intense stress—prolonged drought, overuse of agrochemicals, or strong temperature fluctuations—the turf's defense system suffers. In such cases, Elicitor and biostimulant products become an essential aid to restore balance, reduce damage, and maintain the playability and visual appearance of greens, tees, or football fields.
BestCure and other commercial formulations based on natural extracts
Much of the recent innovation in plant health revolves around formulations that combine direct biocidal activity with elicitor capacityOne example is BestCure, developed from citrus extracts that act in a dual way: they directly control some fungal and bacterial diseases and, at the same time, activate the plant's natural defenses.
These types of products are designed for not to compromise biomass production or yieldThis is precisely because they modulate, in a balanced way, the hormonal pathways involved in defense and growth. In the specific case of BestCure, its ability to activate both Systemic Acquired Resistance (SAR), mediated by salicylic acid, and Systemic Induced Resistance (SIR), linked to jasmonic acid and ethylene, has been described.
The combination of SAR and ISR allows a comprehensive protection against biotrophic and necrotrophic pathogensas well as an improved response to herbivorous insects. Furthermore, by systemically activating defense mechanisms, the plants are "prepared" for future infections, with a reduced impact from each new attack.
What's interesting about this product line is that They fit very well into integrated management programs and sustainable agricultureThey allow for a reduction in the doses of conventional pesticides, improve stress tolerance, and increase the quality and post-harvest life of products, while maintaining high levels of bioactive compounds beneficial to human health.
The development of these formulations is supported by a large volume of research, reflected in Articles and scientific reviews on the role of elicitors in crop protectionfrom both a physiological and molecular perspective. Studies in high-impact journals have delved into its effects on gene expression, fruit metabolomics, and plant-microorganism interactions, as well as its potential for more sustainable crop protection.
All this evidence indicates that natural elicitors—whether botanical extracts, polysaccharides, plant hormones, beneficial microorganisms, gases, or inorganic compounds—offer a A solid way to strengthen the immune system of plants and improve quality, yield and preservationIts correct use, with technical advice, dose adjustment, respect for environmental conditions and compatibility with other management practices, allows for a reduction in the use of synthetic chemicals and progress towards a more resilient, profitable and environmentally friendly agriculture.
