Understanding Biotic Plant Stress: Causes and Symptoms

What is Biotic Plant Stress?

Biotic plant stress is a serious concern for farmers, gardeners, and botanists worldwide. In this blog, we will explore the causes and symptoms of biotic plant stress, including insects, fungi, bacteria, and nematodes. We will also discuss how plants respond to stress and the different signaling pathways that control their interaction with stressors.

Plant Stress is the imbalance between the demand for water, nutrients, and light on a plant. This imbalance can cause plants to undergo a variety of responses that may result in death. Plant stress is a phenomenon that occurs when plants are faced with environmental stresses. These environmental stresses can be categorized into biotic, abiotic, or chemical. Abiotic stresses are caused by non-living factors such as drought and temperature extremes. Biotic stresses are caused by living organisms such as insects and fungi. Chemical stresses involve using pesticides or fertilizers that can lead to plant death if used improperly or in excess.

All plants can succumb to different biotic stressors, including insects that feed on leaves or fruit; fungi like rusts or mildews that cause leaf spots; diseases such as powdery mildew causing yellowing leaves; roundworms such as nematodes (roundworms) that feed on seeds; and plants wilt, turn yellow and die off when they come into contact with bacteria or viruses.

Plants require a multitude of factors to survive, reproduce and grow. One of the most important requirements is an environment that can provide stable conditions. When plants are stationary, they have adapted mechanisms to help them survive in adverse conditions such as drought by sensing when their soil is dry and producing many roots to search for new water sources.

Most crop plants grow in suboptimal environments, meaning they don’t reach their full genetic potential and end up with inhibited metabolic function.

There are many reasons for this. One of them is that the plants are not receiving the right amount of water, nutrients, or sunlight. Another reason is that they are not getting enough plant-based chemicals to help them grow.

What Causes Plant Stress?

Plants can suffer from biotic or abiotic stressors. Other organisms, such as insects, fungi, and bacteria, cause the former. The latter are environmental factors that affect plants, such as water shortage and extreme temperatures.

Biotic stressors:

-Insects: pests such as aphids can suck out the plant’s sap and cause it to secrete a sticky substance called honeydew which attracts sooty mold that blocks sunlight from reaching the leaves.

-Fungi: they may infect a plant’s root system, causing it to rot and depriving it of water and nutrients.

-Bacteria can cause leaf spots on leaves or fruit rot on fruits.

Plants are affected not only by the type of stress they receive but also by the presence or absence of initial or previous stress. Plants would acclimate to previous stress if it were present for long enough, affecting their response to subsequent stress.

The presence of initial or previous stress alters a plant’s normal response to a second stress due to Acclimation. Acclimation is the process by which plants become accustomed to new environmental conditions and develop tolerance.

Fungal parasites are a major source of biotic stress in agriculture and can cause significant crop loss. As the climate changes, the incidence and severity of fungal infections are expected to increase.

The most common type of fungi that infects crops are necrotrophic fungi. These fungi secrete toxins that kill the host cells and release nutrients for them to feed on. However, not all biotrophic fungi are harmful. Some of them can be beneficial by providing nutrients to plants or releasing hormones that help plants defend themselves against disease-causing pathogens. But some of them can be more harmful to plants. The type of fungi that can cause the most damage are white-rot fungi because they change the structure of the wood in a way that prevents it from being able to conduct water or nutrients through its tissues. The wood dries out and then cracks, rotting it away until nothing remains. Fungi thrive in areas without much air circulation, so finding them is easy if you look for them on your plant leaves. Look for brown, orange, or red exudates on the leaves and stems. If you see tan-colored, powdery fungal growth on the surface of your plant, this is a sign of rust.

Nematodes are tiny worms that can cause much damage to plant growth. They feed on plant parts and primarily cause soil-borne diseases leading to nutrient deficiency, stunted growth, and wilt. Nematodes are microscopic worms that live in the soil. They feed on plant roots and other organic matter in the soil, which causes them to develop into a parasite. The nematode will attach itself to the plant’s root and suck out its nutrients, which can lead to stunted growth or wilting.

Plant-Pathogen Recognition

The first level of pathogen recognition encompasses pattern recognition receptors. Plant cells have receptors that are sensitive to the presence of certain molecules and toxins. These receptors can detect the presence of pathogens or other biotic stresses like drought, salinity, or cold temperature.

Plant cells have receptors that are sensitive to the presence of certain molecules and toxins. These receptors can detect the presence of pathogens or other abiotic stresses like drought, salinity, or cold temperature.

The second level of pathogen recognition encircles plant resistance (R) proteins, which identify specific receptors from a pathogen. These receptors are found on the plasma membrane of plant cells and distinguish between self and non-self. The R protein is a type of immune protein. Binding between the pathogen and the receptor, an external protein on the surface of a cell, will activate an immune response.

A gene present can encode the R protein in plants’ genome or be acquired from an external source, such as a bacterium. This means that plants have evolved mechanisms to acquire resistance genes from their environment. Induced resistance is a form of plant defense when an external agent provokes the plant to produce a mutated version of the R protein. This mutated protein confers protection against the agent. For example, certain bacteria-like molecules have improved plants’ ability to resist damage caused by pathogens or environmental stresses such as drought, flooding, and frost. These molecules can be reactive oxygen species (ROS) like hydrogen peroxide, superoxide, and nitric oxide, which elicit very strong oxidative signals,  forming lipid peroxidation products (L-1).

Oxygen-containing free radicals (ROO) can react with lipids in cell membranes, causing lipid peroxidation. Lipid hydroperoxides can form several oxidation products. These products include lipid and aldehyde radicals, nitrosyl radicals, 2-hydroxyalkenals, and 2-hydroxyalkanes. The most reactive lipid hydroperoxides are peroxy fatty acids and OOOHs, which can react with water molecules to form hydroxyl and hydrogen peroxide (HO2).

Hormone Signaling Pathways in Plants

Plant hormones are chemicals that control the growth, development, and reproduction of plant organs. Plants produce auxin in various parts of the plant, including the roots. Auxin is a plant hormone that regulates many aspects of plant growth and development, including stem elongation. Hormones are transported throughout the plant by a signaling system composed of two interconnected pathways: the phytohormone signaling pathway and the systemic signaling pathway.

The phytohormone signaling pathway is a process that regulates the growth, development, and response of plants to external stimuli. The signaling pathway is composed of different levels of regulation. One level of regulation includes the interaction between hormones and receptors on the plasma membrane, and another level includes soluble factors in the cytosol, such as auxin and ethylene. Furthermore, this pathway is mediated by hydrolysis or root-to-shoot movement of IAA (indole-3-acetic acid).

The signaling pathway is a biochemical process that happens in plants and animals. It is essential for the growth and development of the plant, as well as for the plant’s response to various stresses.

The signaling pathway is a series of chemical reactions that starts with a signal molecule binding to a receptor on the surface of the cell membrane. This binding triggers a cascade of events that lead to gene expression and cell behavior changes.

The signaling pathway can be summarized into five steps:

1) The signal molecule binds to its receptor on the surface of the cell membrane 2) this binding triggers a cascade of events that lead to changes in gene expression and cell behavior; 3) these changes trigger other chemical reactions, including those which produce hormones or other signals; 4) these signals trigger further changes in gene expression; 5) these changes may eventually lead to programmed cell death or differentiation into another type of cell.

Symptoms of Plant Stress

Plant stress is a common problem when plants do not get the right water, nutrients, or light. If you don’t diagnose the problem early enough, it can lead to the death of your plant.

The most common signs of plant stress include:

– Dry brown leaves

– Wilting leaves

– Yellowing leaves

– Curled or bent leaves

The signaling pathways that control the interaction between stress and plants are poorly understood. However, a plant’s response to stress depends on the hormone-signaling pathway activated by the stressor.

It has been found that some signaling pathways (such as salicylic acid) induce defense responses in plants while others (such as jasmonic acid) activate growth responses. This means that different signals can have opposite effects on plant development, depending on which pathway they activate.

Plants are living organisms that can be affected by several different biotic stressors. These stressors can range from physical to chemical and from infectious to non-infectious. The best way to treat these plants is by preventing them in the first place, but if they do happen, it is important to know how to treat them properly. The most common biotic stressors are insects, mites, nematodes, and fungi, and these can be prevented by using pesticides or other methods.

The first step is to identify the biotic stressor. The second step is to prevent the biotic stressor from attacking the plant in the first place by using pesticides or other methods. 

Plants have one of the world’s most complex and sophisticated systems to deal with predators. This system includes a chemical signaling network that controls plant responses to different stressors. Plants do not have just one type of defense response but rather two: growth responses and defense responses. Some plant defenses are simple cell death, programmed cell death (PCD), or callose. Such a defense can be induced by extreme cold, heat, and fire, as well as by herbivores. In response to these different stresses, cells undergo PCD, and the plant regenerates. Other complex defenses include resistance to pathogens and insects, resin production that protects against herbivores and pathogen damage, and toxic phytochemicals in plants’ leaves that deter animals from eating them. Physical defenses include thorns, spines, barbs, and horns that deter incursion and production of volatile chemicals that repel or kill some small animals. Chemical defenses include the production of irritating compounds that ward off animals with less developed senses, such as insects, bacteria, or fungi. Terrestrial plants use various glands in their leaves to produce chemical defense compounds such as caffeine which is used as a natural pesticide.

Further Reading

  1. Ramegowda, V., & Senthil-Kumar, M. (2015). The interactive effects of simultaneous biotic and abiotic stresses on plants: Mechanisms and prospects for improvement. Frontiers in plant science, 6, 718.
  2. Pieterse, C. M., Zamioudis, C., Berendsen, R. L., Weller, D. M., Van Wees, S. C., & Bakker, P. A. (2014). Induced systemic resistance by beneficial microbes. Annual review of phytopathology, 52, 347-375.
  3. Wu, J., & Baldwin, I. T. (2010). New insights into plant responses to the attack from insect herbivores. Annual review of genetics, 44, 1-24.
  4. Glazebrook, J. (2005). Contrasting mechanisms of defense against biotrophic and necrotrophic pathogens. Annual review of phytopathology, 43, 205-227.
  5. Stam, R., & van Loon, L. C. (2012). Plant interactions with multiple insect herbivores: from community to genes. Annual review of plant biology, 63, 689-713.
  6. Kunkel, B. N., & Brooks, D. M. (2002). Cross talk between signaling pathways in pathogen defense. Current opinion in plant biology, 5(4), 325-331.
  7. Williamson, B., Tudzynski, B., Tudzynski, P., & van Kan, J. A. (2007). Botrytis cinerea: the cause of grey mould disease. Molecular plant pathology, 8(5), 561-580.
  8. Patel, J. S., & Singh, H. B. (2013). Plant nematode interaction: a review. Journal of Applied and Natural Science, 5(1), 157-162.

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