Plant Defense Activators

Inducing Systemic Acquired Resistance (SAR)
One of the primary mechanisms through which PDAs operate is by inducing systemic acquired resistance (SAR). SAR is a long-lasting and broad-spectrum defense response in plants. When a plant is exposed to a PDA, it triggers a cascade of biochemical events that lead to the production of defense-related compounds.

Activation of Defense-Related Genes
PDAs can activate specific genes in the plant that are responsible for the synthesis of proteins and metabolites involved in defense responses. These genes may code for enzymes, antimicrobial compounds, and signaling molecules that play crucial roles in plant defense.

Production of Secondary Metabolites
PDAs often stimulate the production of secondary metabolites in plants. These metabolites can have antimicrobial, antifungal, or insecticidal properties, acting as chemical defenses against invading pathogens or pests.

Enhanced Cell Wall Strength
Some PDAs contribute to the reinforcement of the plant cell wall. A stronger cell wall can act as a physical barrier, making it more difficult for pathogens to penetrate plant tissues.

Activation of Phytohormones
PDAs may influence the levels of plant hormones such as salicylic acid (SA), jasmonic acid (JA), and ethylene. These hormones play key roles in signaling and regulating defense responses. The interplay of these hormones helps coordinate an effective defense strategy.

Recruitment of Beneficial Microorganisms
Some PDAs promote the recruitment and activity of beneficial microorganisms, such as mycorrhizal fungi and plant growth-promoting bacteria (PGPB). These microorganisms can establish symbiotic relationships with plants, enhancing nutrient uptake and providing protection against pathogens.

Priming the Immune System
PDAs can "prime" the plant's immune system, essentially preparing it for a more rapid and robust response upon subsequent exposure to pathogens or stressors. This priming effect allows the plant to mount a quicker and more efficient defense when needed.

Reduction of Oxidative Stress
PDAs may help reduce oxidative stress within plant cells. By promoting the production of antioxidants, they enhance the plant's ability to neutralize reactive oxygen species (ROS) generated during stress conditions.

Storage Conditions
Store PDAs in a cool, dry place according to the manufacturer's recommendations. Exposure to extreme temperatures, humidity, or direct sunlight can degrade the quality of the product.

Container Integrity
Ensure that the containers holding the PDAs are tightly sealed to prevent moisture or contaminants from entering. Damaged or compromised containers can compromise the quality of the product.

Avoid Contamination
Use clean and dedicated equipment when handling PDAs. Prevent contamination by avoiding contact with other chemicals, fertilizers, or pesticides. Follow proper equipment cleaning procedures between different applications.

Check Expiry Dates
Always check the expiration date on the product label. Using PDAs past their expiration date can result in reduced effectiveness. If the product has expired, dispose of it properly according to local regulations.

Follow Mixing Guidelines
If the PDA requires mixing before application, strictly adhere to the recommended guidelines for proper dilution. Follow the mixing instructions on the label to achieve the desired concentration.

Adherence to Application Rates
Follow the recommended application rates provided on the product label. Using more than the recommended amount may not provide additional benefits and could lead to waste or adverse effects.

Compatible Tank Mixtures
If you plan to mix PDAs with other agricultural inputs, such as fertilizers or pesticides, check compatibility. Some products may have guidelines to ensure compatibility and avoid adverse reactions.

Equipment Calibration
Calibrate application equipment regularly to ensure accurate and uniform distribution of PDAs. Proper calibration helps prevent under-application or over-application in different areas of the field.

Record Keeping
Keep detailed records of PDA applications, including dates, rates, and specific conditions. These records are valuable for tracking the effectiveness of the product and making informed decisions for future applications.

Monitor Crop Response
Regularly monitor the crop for signs of diseases, pests, or stress. If issues persist despite PDA applications, reassess the product or consider adjustments in application methods.

Themselves
With so many creatures trying to attack them, you can imagine that plants have a hard time surviving. Since plants cannot flee from their attackers, they had to evolve ways of defending themselves. Plants have developed several defenses against herbivores. Some plant defensesFeatures of a plant that affect the behavior, growth, or survival of herbivores. are easy to see, like the thorns of a rose, the hairs on the leaf of a stinging nettle, or the thick skin of beetroots. Other defenses, such as chemical defenses, are less visible. Each plant produces thousands of different chemicals, all involved in essential processes. Some chemicals, like sugars, provide energy to the plant. Other groups of chemicals help to defend plants against attackers. These chemical defenses can make the plant taste bad, which prevents herbivores from eating plant tissues. In some cases, the chemicals can even be toxic. Chemical defenses can affect humans too. There are many plants that would make you feel very sick if you ate them, for example the berries of black nightshade. Some plants, such as poison ivy or hogweed, can give you a rash and even cause burns when you touch them. Most chemical defenses are not that bad, though. In fact, chances are high that you have been exposed to plant chemical defenses yourself.
We have grown to like the taste of some chemicals that plants produce. Have you ever put mustard on your hotdog or sausage, or enjoyed a nice Indian curry with mustard seeds? The sharp-bitter taste of mustard is caused by defense chemicals called glucosinolatesDefense substances responsible for the sharp bitter taste of mustard and wasabi. Although most humans enjoy their taste, they are toxic to most insects, nematodes and bacteria.. In the wild, glucosinolates help plants to defend themselves against insects, fungi, and bacteria. The caffeine in coffee, which helps people to wake up in the morning, is not made by coffee trees to please humans. In reality, coffee trees produce caffeine to protect their seeds-the coffee beans-from insect attacks. Caffeine not only gives coffee beans their bitter taste, but it can also paralyze or kill insects trying to feed on them.
These examples illustrate that chemical defenses are an effective way for plants to protect themselves against herbivores in their environments. Nevertheless, most plants are not completely defended by these chemicals. If you take a good look at the plants around you, you will notice that most plants show some damage, such as holes in their leaves. This is because the production of chemical defenses comes at a cost. Plants do not only have to worry about defending themselves, but they must also put energy into growth, producing flowers, and making seeds. So, the energy plants can spend on producing defenses is limited. Plants must make use of this limited amount of energy in an efficient way.

Themselves Efficiently
Fossils of herbivore-damaged leaves show that plants and herbivores have been living together on Earth for more than 400 million years. During this time, plants have developed several ways to produce defenses in a cost-efficient manner. One way is to produce defenses only when necessary, for example, when insects start eating them [2]. By only producing defenses when under attack, plants save energy when no dangers are present. The disadvantage of this strategy is that defense production will only begin after the herbivore starts eating. Because defense production takes time, the plant can suffer significant damage before the herbivore leaves or dies.
Another strategy is to always have some defenses at hand but in limited amounts. In this case, the plant moves most defenses to the plant parts that are most important for survival and are vulnerable to attack by herbivores [3]. This would be like defending a castle by putting the soldiers on the outer wall, where the first attack would occur and where the castle is most vulnerable. Clearly, the treasure in the castle would be well guarded too, as this is the most valuable. Aboveground, such valuable plant parts include young leaves, flowers, and seeds, which play essential roles in energy production or in producing the next generation.
Belowground, various parts of the root system also have different values. The root systems of plants like tomato or cabbage consist of three parts: the taprootMain root from which lateral roots arise. Collects water and nutrients from the rest of the root system and distributes them aboveground. In carrots and beetroots, it stores starch and nutrients., lateral roots, and fine roots. Lateral and fine roots help the plant take up valuable nutrients and water from the soil. The taproot is the main root that collects all the water and nutrients absorbed by the lateral and fine roots and distributes them to the aboveground parts. Simultaneously, sugars and other substances produced in the leaves move through the taproot in the other direction. The important role of the taproot in transport of nutrients and water makes it an essential part of the root system. When herbivores damage the taproot, the essential transport routes are broken, and the plant will die. In plants like beets, the taproot stores energy in the form of sugar. This is like the treasure in the castle. The taproot is therefore considered the most valuable root part and is defended the most, followed by the lateral and fine roots.

Affect Soil Herbivores
Herbivores decide which root part to eat based both on its nutritional value and on how well it is defended [5]. Most herbivores would prefer to feed on the taproot since it is the most nutritious part of the root system. However, as mentioned earlier, the taproot is also the best-defended part. Not all herbivores can overcome these chemical defenses. Some herbivores, like the larvae of the cabbage root fly, can deactivate chemical defenses and feed on the taproot [4]. Other herbivores, like the larvae of the European June beetle, cannot deal with the high defense levels in the taproot and instead eat the lateral and fine roots (Figure 2). The distribution of chemical defenses across the root system and the ability of herbivores to overcome these defenses can therefore have a strong influence on where herbivores can be found in the soil.