10.2 Biopesticides and biofertilizers
3 min read•august 7, 2024
Biopesticides and biofertilizers are game-changers in sustainable agriculture. They use natural microbes and plant-derived substances to control pests and boost crop growth, reducing the need for harsh chemicals and synthetic fertilizers.
These eco-friendly alternatives work with nature, not against it. From Bt toxins that target specific pests to nitrogen-fixing bacteria that feed plants, they offer smart solutions for farmers looking to protect crops and improve yields sustainably.
Biopesticides
Microbial Pest Control Agents
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- Microbial pesticides are naturally occurring or genetically modified microorganisms (bacteria, fungi, viruses, or protozoa) that suppress pests and plant diseases
- (Bt) is a common bacterial biopesticide that produces crystal proteins toxic to certain insect larvae (lepidopteran, coleopteran, and dipteran pests)
- Bt crystal proteins bind to specific receptors in the insect gut, causing pores to form and leading to cell lysis and death
- Bt toxins are highly specific to target pests and have minimal impact on non-target organisms (beneficial insects, mammals, birds)
- infect and kill insects by penetrating their cuticle, growing inside their body, and producing toxins
- Examples include and , which target a wide range of insect pests (aphids, thrips, whiteflies, and beetles)
- These fungi can be applied as spores or formulated into biopesticide products for spray applications
Genetically Engineered Biopesticides
- (PIPs) are pesticidal substances produced by plants through genetic engineering
- Common PIPs include (corn, cotton, soybeans) that express Bt toxins in their tissues, providing built-in protection against target pests
- Bt crops have significantly reduced the need for synthetic insecticide applications in many cropping systems
- Other PIPs may include transgenic plants expressing antifungal proteins, viral coat proteins for virus resistance, or enzymes that degrade fungal cell walls
Biofertilizers and Plant Growth Promoters
Microbial Inoculants for Nutrient Acquisition
- Nitrogen-fixing bacteria form symbiotic relationships with leguminous plants (soybeans, alfalfa, clover) and convert atmospheric nitrogen (N2) into plant-available forms (ammonia)
- and are common genera of nitrogen-fixing bacteria used as biofertilizers for legume crops
- Inoculating legume seeds or soil with these bacteria enhances and reduces the need for synthetic nitrogen fertilizers
- form mutualistic associations with plant roots, extending the root system and improving nutrient and water uptake
- (AMF) colonize the roots of most land plants and exchange nutrients (phosphorus, nitrogen, micronutrients) for plant-derived carbon
- (EMF) associate with many tree species (pines, oaks, eucalyptus) and enhance nutrient acquisition in forest ecosystems
Plant Growth-Promoting Rhizobacteria (PGPR)
- colonize plant roots and stimulate growth through various mechanisms, including nutrient solubilization, phytohormone production, and pathogen suppression
- Examples of PGPR include , Bacillus, and Azospirillum species, which can be applied as seed treatments or soil inoculants
- Pseudomonas fluorescens produces siderophores that chelate iron and make it more available to plants, promoting growth in iron-deficient soils
- produces antibiotics and enzymes that suppress soil-borne pathogens (Fusarium, Pythium, Rhizoctonia) and induce systemic resistance in plants
Environmental Applications
Bioremediation Using Microorganisms
- involves the use of microorganisms to degrade or detoxify environmental pollutants (petroleum hydrocarbons, pesticides, heavy metals)
- Bacteria and fungi possess diverse metabolic capabilities that allow them to break down complex organic compounds and transform them into less toxic or non-toxic substances
- is a common bacterial species used in bioremediation of oil spills and hydrocarbon-contaminated soils
- White-rot fungi (, ) produce lignin-degrading enzymes that can also degrade persistent organic pollutants (PCBs, PAHs, dioxins)
- Bioremediation strategies include (adding nutrients to stimulate indigenous microbial populations) and (introducing specific microorganisms with desired degradative capabilities)
- Biostimulation of oil-contaminated beaches with fertilizers containing nitrogen and phosphorus accelerates the breakdown of petroleum hydrocarbons by native bacteria
- Bioaugmentation of pesticide-contaminated soils with Sphingomonas species that can degrade organophosphate insecticides (chlorpyrifos, parathion) enhances the rate of pesticide removal
Key Terms to Review (24)
Arbuscular mycorrhizal fungi: Arbuscular mycorrhizal fungi (AMF) are a group of fungi that form symbiotic relationships with the roots of most terrestrial plants, facilitating nutrient exchange and enhancing plant growth. These fungi penetrate the root cells and create specialized structures called arbuscules, which increase the surface area for nutrient absorption, particularly phosphorus. This mutualistic relationship not only benefits the plants by improving nutrient uptake but also enhances soil structure and health.
Bacillus subtilis: Bacillus subtilis is a Gram-positive, rod-shaped bacterium known for its ability to form endospores and its role in soil health and plant growth promotion. This bacterium is widely recognized for its beneficial applications as a biopesticide and biofertilizer, enhancing agricultural productivity while being environmentally friendly.
Bacillus thuringiensis: Bacillus thuringiensis, often abbreviated as Bt, is a soil-dwelling bacterium known for its insecticidal properties. This bacterium produces crystal proteins that are toxic to various insect pests, making it a key player in the development of biopesticides and transgenic crops designed to resist pest damage. Its use in agriculture promotes sustainable practices by reducing reliance on chemical pesticides, leading to positive impacts in both environmental health and food production.
Beauveria bassiana: Beauveria bassiana is a filamentous fungus that is widely recognized as an effective biopesticide used in agricultural practices. This entomopathogenic fungus infects and kills a variety of insect pests, making it an important tool in sustainable pest management strategies. It operates by producing spores that attach to the cuticle of insects, germinate, and invade their tissues, ultimately leading to the insect's death. By using Beauveria bassiana, farmers can reduce reliance on chemical pesticides, promoting a healthier environment.
Bioaugmentation: Bioaugmentation is a bioremediation process that involves the addition of specific microorganisms to contaminated environments to enhance the degradation of pollutants. This technique aims to improve the natural processes of microbial degradation by introducing strains that have desirable traits, such as the ability to metabolize toxic substances or outcompete native microbes. By doing so, bioaugmentation can effectively restore polluted sites and contribute to soil and water health.
Bioremediation: Bioremediation is the process of using living organisms, typically microbes, to degrade or remove pollutants from the environment, thereby restoring contaminated sites to a natural state. This method is particularly effective in addressing issues like oil spills, heavy metal contamination, and agricultural runoff by harnessing the natural metabolic processes of microorganisms.
Biostimulation: Biostimulation refers to the process of enhancing the activity of indigenous microorganisms in the environment to improve their ability to degrade pollutants or promote plant growth. This is typically achieved by adding nutrients or other stimulants that increase microbial metabolism and reproduction, leading to more effective bioremediation or enhanced agricultural productivity. It plays a crucial role in both environmental management and sustainable agriculture.
Bradyrhizobium: Bradyrhizobium is a genus of bacteria known for its ability to form symbiotic relationships with leguminous plants, particularly through the formation of root nodules where nitrogen fixation occurs. These bacteria play a crucial role in agriculture by enhancing soil fertility and providing an eco-friendly alternative to chemical fertilizers.
Bt crops: Bt crops are genetically modified plants that have been engineered to express a toxin derived from the bacterium Bacillus thuringiensis, which serves as a biopesticide against specific pests. This modification allows the crops to naturally resist insect damage, reducing the need for chemical insecticides and enhancing crop yield and sustainability in agricultural practices.
Ectomycorrhizal fungi: Ectomycorrhizal fungi are a type of fungi that form symbiotic relationships with the roots of many trees and shrubs, creating a network that enhances nutrient uptake for the plant while receiving carbohydrates in return. This relationship is critical for plant health, especially in nutrient-poor soils, as these fungi improve water absorption and increase access to essential minerals like phosphorus and nitrogen. They play a key role in forest ecosystems and are often involved in promoting plant growth and resilience.
Entomopathogenic fungi: Entomopathogenic fungi are specialized fungi that infect and kill insects, serving as a natural form of pest control. These fungi can be used in agriculture as biopesticides, offering an environmentally friendly alternative to synthetic pesticides. By targeting specific insect pests, they help reduce crop damage while promoting sustainable farming practices.
Field Efficacy: Field efficacy refers to the effectiveness of a biopesticide or biofertilizer in real-world agricultural settings, demonstrating its ability to provide desired results under varied environmental conditions. This concept is crucial for assessing the practical applications and benefits of biopesticides and biofertilizers, as laboratory results may not always translate directly to field performance. Understanding field efficacy helps farmers make informed decisions about product usage and management practices.
Metarhizium anisopliae: Metarhizium anisopliae is a soil-dwelling fungus that acts as a natural biopesticide, targeting various insect pests, particularly in agriculture. This fungus infects insects upon contact, leading to their death, and is a sustainable alternative to chemical pesticides, contributing to integrated pest management strategies.
Microbial biopesticides: Microbial biopesticides are natural pesticides derived from microorganisms, such as bacteria, fungi, and viruses, used to control pests in agriculture. They provide an eco-friendly alternative to chemical pesticides by utilizing the natural properties of these organisms to target specific pests while minimizing harm to beneficial insects, plants, and the environment. Their use promotes sustainable agriculture practices by reducing chemical residues and supporting biodiversity in farming systems.
Mycorrhizal fungi: Mycorrhizal fungi are beneficial fungi that form symbiotic relationships with the roots of plants, enhancing nutrient absorption, particularly phosphorus. This partnership is crucial for plant health, allowing for improved water uptake and resistance to soil pathogens, while the fungi receive carbohydrates from the plants as a food source, creating a mutually beneficial arrangement.
Nitrogen fixation: Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into a form that plants can use, typically ammonia (NH₃) or related compounds. This process is vital for agriculture and the ecosystem because most plants cannot utilize atmospheric nitrogen directly. Nitrogen-fixing bacteria, often found in root nodules of legumes or in soil, play a crucial role in this conversion, making it essential for sustainable farming practices and enhancing soil fertility.
PGPR: PGPR stands for Plant Growth-Promoting Rhizobacteria, which are beneficial bacteria that colonize plant roots and enhance plant growth by various mechanisms. These bacteria improve nutrient availability, stimulate root development, and can even help plants resist pathogens, making them valuable for sustainable agriculture and biofertilizer applications.
Phanerochaete chrysosporium: Phanerochaete chrysosporium is a white-rot fungus known for its ability to decompose lignin and other complex organic materials. This organism plays a significant role in the environment by breaking down tough plant materials, which can be harnessed for biopesticides and biofertilizers, thus contributing to sustainable agricultural practices and waste management solutions.
Plant growth-promoting rhizobacteria: Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that inhabit the rhizosphere, the region of soil near plant roots, and enhance plant growth by various mechanisms. These bacteria can promote nutrient uptake, improve soil structure, and help plants withstand environmental stresses, making them a crucial component of sustainable agriculture and effective biofertilization strategies.
Plant-incorporated protectants: Plant-incorporated protectants are a type of biopesticide that are genetically engineered into plants to provide them with built-in defenses against pests and diseases. This technology allows crops to express specific proteins that can deter, repel, or kill insects and pathogens, reducing the need for external pesticide applications. These protectants play a crucial role in sustainable agriculture by enhancing crop resilience and productivity while minimizing chemical inputs.
Pseudomonas: Pseudomonas is a genus of bacteria known for its metabolic versatility and ability to thrive in various environments, including soil, water, and even plant and animal hosts. Some species within this genus are used as biopesticides and biofertilizers due to their beneficial properties, such as promoting plant growth and suppressing plant pathogens.
Pseudomonas putida: Pseudomonas putida is a versatile, non-pathogenic bacterium known for its ability to degrade a variety of environmental pollutants, making it valuable in bioremediation and agricultural practices. This bacterium can break down toxic compounds, like hydrocarbons and phenols, and is also used in the production of biofertilizers and biopesticides, helping to enhance soil health and plant growth.
Rhizobium: Rhizobium is a genus of bacteria that forms a symbiotic relationship with leguminous plants, aiding in nitrogen fixation. This process transforms atmospheric nitrogen into a form that plants can utilize, significantly enhancing soil fertility and promoting plant growth, thus connecting it to the use of biofertilizers in sustainable agriculture.
Trametes versicolor: Trametes versicolor, commonly known as the turkey tail mushroom, is a polypore fungus that is widely recognized for its colorful, fan-like fruiting bodies. It is significant in the context of biopesticides and biofertilizers due to its potential applications in sustainable agriculture, particularly for promoting plant health and controlling pests through natural means.