Mycorrhiza and its Application PDF

3.4 Fungal symbioses: Mycorrhiza Mycorrhiza refers to a symbiotic association between a fungus and the roots of a vascular plant. In this mutually beneficial relationship, the fungus assists the plant with nutrient and water absorption, while the plant provides the fungus with carbohydrates produced...

3.4 Fungal symbioses: Mycorrhiza Mycorrhiza refers to a symbiotic association between a fungus and the roots of a vascular plant. In this mutually beneficial relationship, the fungus assists the plant with nutrient and water absorption, while the plant provides the fungus with carbohydrates produced through photosynthesis. This relationship is fundamental to the health and productivity of many plants, including most agricultural and forest species. According to Peterson and Farquhar (1994) along with examples: 1. Ectomycorrhizae (ECM) Description: Ectomycorrhizae form a sheath, or mantle, around the root tips of their host plants. The fungal hyphae penetrate the root cortex but do not enter the root cells. Instead, they form an intercellular network known as the Hartig net around the cortical cells. Structure: Mantle: A thick layer of fungal tissue surrounding the root tips. Hartig Net: An intricate network of hyphae surrounding the plant's cortical cells within the root. Hosts: Commonly associated with woody plants, particularly trees such as pines (Pinus spp.), oaks (Quercus spp.), and birches (Betula spp.). Examples: Pisolithus tinctorius: A common ectomycorrhizal fungus that forms associations with various tree species, enhancing their nutrient and water uptake. Boletus edulis (King Bolete): Forms ectomycorrhizal associations with pines and other conifers. Benefits: Enhanced Nutrient Uptake: Increases the uptake of nutrients, especially phosphorus and nitrogen. Water Absorption: Improves water uptake and drought resistance. Disease Resistance: Provides protection against soil-borne pathogens. 1 2. Vesicular-Arbuscular Mycorrhizae (VAM) or Arbuscular Mycorrhizae (AM) Description: Arbuscular mycorrhizal fungi (AMF) penetrate the cortical cells of the host plant's roots, forming specialized structures known as arbuscules and vesicles. Arbuscules facilitate nutrient exchange between the fungus and the plant, while vesicles serve as storage organs. Structure: Arbuscules: Branched, tree-like structures formed within the root cells for nutrient exchange. Vesicles: Spherical structures within the root cells that store lipids and other nutrients. Hosts: Found in a wide range of herbaceous plants, grasses, and agricultural crops. Examples: Glomus intraradices: An arbuscular mycorrhizal fungus commonly associated with many crop plants, improving their growth and nutrient uptake. Rhizophagus irregularis: Another widely studied AM fungus that forms symbiotic relationships with many terrestrial plants. Benefits: Enhanced Phosphorus Uptake: Significantly increases phosphorus uptake, which is crucial for plant growth and development. Improved Soil Structure: Helps in soil aggregation and stability. Disease Suppression: Reduces the incidence of root diseases by outcompeting pathogens. 3. Ectendomycorrhizae (Arbutoid Mycorrhizae) Description: Ectendomycorrhizae, also known as arbutoid mycorrhizae, exhibit characteristics of both ectomycorrhizae and endomycorrhizae. These fungi form a mantle around the root tips, similar to ectomycorrhizae, and their hyphae penetrate the cortical cells, forming intracellular coils. 2 Structure: Mantle: A fungal sheath around the root tips. Intracellular Hyphal Coils: Hyphae penetrate the cortical cells and form coils. Hosts: Commonly found in the Ericaceae family, including plants such as Arbutus and Arctostaphylos. Examples: Arbutus menziesii (Pacific madrone): Forms ectendomycorrhizal associations that enhance nutrient uptake and soil stabilization. Arctostaphylos uva-ursi (Bearberry): A plant that forms arbutoid mycorrhizal associations. 4. Ericoid Mycorrhizae Description: Ericoid mycorrhizal fungi form associations with the roots of plants in the Ericaceae family. The fungi form hyphal coils within the root epidermal cells, aiding in the decomposition of organic matter and nutrient absorption. Structure: Hyphal Coils: Intracellular coils formed within the root epidermal cells. Hosts: Plants in the Ericaceae family, such as blueberries (Vaccinium spp.) and heather (Calluna vulgaris). Examples: Rhizoscyphus ericae: A fungus that forms ericoid mycorrhizal associations with various ericaceous plants, helping them thrive in nutrient-poor and acidic soils. Hymenoscyphus ericae: Another ericoid mycorrhizal fungus found in association with ericaceous plants. 3 5. Orchid Mycorrhizae Description: Orchid mycorrhizal fungi form associations with the roots of orchids. These fungi are essential for orchid seed germination and early development, as orchid seeds lack sufficient nutrient reserves. Structure: Pelotons: Coiled hyphal structures formed within the root cells of orchids. Hosts: Orchidaceae family (orchids). Examples: Rhizoctonia spp.: Common fungi that form orchid mycorrhizal associations with various orchid species, providing essential nutrients for their growth. Ceratobasidium cornigerum: Another fungus that forms mycorrhizal associations with orchids. 6. Arbutoid Mycorrhizae Description: These mycorrhizae are similar to ectomycorrhizae but are specifically associated with certain plant families such as Ericaceae. They form a dense hyphal sheath around the roots and also penetrate the root cells. Structure: Hyphal Sheath: Dense fungal sheath surrounding the root tips. Intracellular Hyphae: Hyphae penetrate the root cells, forming coils or pelotons. Hosts: Plants like Arbutus and Arctostaphylos. Examples: Arbutus menziesii (Pacific madrone): Forms arbutoid mycorrhizal associations that enhance nutrient uptake and soil stabilization. Arctostaphylos uva-ursi (Bearberry): A plant that forms arbutoid mycorrhizal associations. 4 7. Monotropoid Mycorrhizae Description: Monotropoid mycorrhizae are found in plants within the Monotropaceae family. These mycorrhizae form a dense hyphal sheath around the roots, and the fungi invade the root cells. Structure: Hyphal Sheath: Dense fungal sheath surrounding the root tips. Intracellular Hyphae: Hyphae penetrate the root cells, forming coils or pelotons. Hosts: Plants like Monotropa and Sarcodes. Examples: Monotropa uniflora (Indian Pipe): A plant that forms monotropoid mycorrhizal associations, relying entirely on mycorrhizal fungi for nutrient acquisition. Sarcodes sanguinea (Snow Plant): Another plant that forms monotropoid mycorrhizal associations. 5  Fungal symbioses: Mycorrhiza and their importance Enhanced Nutrient Uptake: Phosphorus Uptake: Description: Mycorrhizal fungi significantly enhance the availability and absorption of phosphorus, a crucial nutrient for plant growth and development. Example: Arbuscular Mycorrhiza (AM): In crops like maize (Zea mays), arbuscular mycorrhizal fungi such as Glomus intraradices form symbiotic relationships with the roots. The fungal hyphae extend far into the soil, accessing phosphorus that is otherwise unavailable to the plant roots. This improved phosphorus uptake results in better growth and higher yields. Nitrogen Uptake: Description: Mycorrhizae assist in the uptake of nitrogen, which is essential for plant protein synthesis and overall growth. Example: Ectomycorrhiza (ECM): In forest trees like pines (Pinus spp.) and oaks (Quercus spp.), ectomycorrhizal fungi such as Pisolithus tinctorius enhance the uptake of both inorganic and organic nitrogen forms. This symbiosis allows trees to thrive in nutrient-poor soils by improving their nitrogen acquisition. Improved Water Uptake: Description: The extensive network of fungal hyphae increases the surface area for water absorption, helping plants access water more efficiently, especially in drought conditions. Example: Ectomycorrhiza (ECM): Ectomycorrhizal fungi associated with birch trees (Betula spp.) enhance the drought resistance of the trees by improving their water uptake. The fungal hyphae penetrate deeper into the soil than the plant roots alone, accessing water in dry periods. Soil Structure Improvement: Description: Mycorrhizal fungi contribute to soil aggregation by producing a glycoprotein called glomalin, which binds soil particles together, improving soil structure and stability. Example: Arbuscular Mycorrhiza (AM): In agricultural fields, arbuscular mycorrhizal fungi improve soil structure, enhancing soil aeration, water infiltration, and root penetration. This leads to healthier soil ecosystems and better plant growth. 6 Disease Resistance: Description: Mycorrhizae protect plants against soil-borne pathogens by outcompeting harmful microorganisms for space and nutrients or by inducing systemic resistance in the host plant. Example: Arbuscular Mycorrhiza (AM): In tomato plants (Solanum lycopersicum), arbuscular mycorrhizal fungi like Glomus mosseae reduce the incidence of root rot caused by pathogenic fungi. The mycorrhizal association enhances the plant's immune response, providing greater resistance to infections. Enhanced Plant Growth and Yield: Description: The improved nutrient and water uptake, along with enhanced disease resistance, leads to overall better growth, vigor, and yield of plants. Example: Arbuscular Mycorrhiza (AM): In soybean (Glycine max), inoculation with arbuscular mycorrhizal fungi like Rhizophagus irregularis increases root biomass, nutrient uptake, and ultimately seed yield. This results in higher crop productivity and improved agricultural sustainability. Biodiversity and Ecosystem Functioning: Description: Mycorrhizae play a crucial role in maintaining plant diversity and ecosystem stability by facilitating nutrient cycling and enhancing plant community resilience. Example: Ectomycorrhiza (ECM): In mixed forests, ectomycorrhizal fungi form networks (mycorrhizal networks) that connect different tree species, allowing for nutrient exchange and improving forest health and biodiversity. This interconnectedness supports a diverse and resilient forest ecosystem. Phytoremediation: Description: Mycorrhizal fungi can assist in the phytoremediation of contaminated soils by helping plants tolerate and accumulate heavy metals and other pollutants. Example: Arbuscular Mycorrhiza (AM): Arbuscular mycorrhizal fungi have been used in phytoremediation projects to help plants like willows (Salix spp.) and poplars (Populus spp.) grow in soils contaminated with heavy metals such as cadmium and lead. The fungi enhance the plants' ability to tolerate and accumulate these contaminants, aiding in environmental cleanup. 7 Applications in Agriculture: 1. Sustainable Agriculture: o Description: Mycorrhizae are used in sustainable farming practices to reduce the need for chemical fertilizers and pesticides. o Example: Inoculating maize fields with arbuscular mycorrhizal fungi reduces the need for phosphorus fertilizers, promoting sustainable crop production and reducing environmental impact. 2. Horticulture: o Description: Mycorrhizal inoculants are used to improve the growth and health of ornamental plants, trees, and shrubs. o Example: Mycorrhizal inoculants are applied to nursery-grown ornamental plants like roses (Rosa spp.) to enhance their establishment, growth, and resistance to soil-borne diseases. 3. Forestry: o Description: Mycorrhizae are critical for the establishment and growth of forest trees, aiding in reforestation and afforestation efforts. o Example: Ectomycorrhizal fungi are used in reforestation projects to improve the survival and growth of tree seedlings in degraded lands, supporting forest regeneration and ecosystem recovery. 4. Crop Production: o Description: Mycorrhizal fungi are used to enhance the growth and yield of crops such as maize, wheat, rice, and legumes. o Example: Inoculating wheat fields with arbuscular mycorrhizal fungi improves nutrient uptake and grain yield, enhancing overall crop productivity and food security 8