Definition of Glomeromycota
Glomeromycota is a group of fungi that are mostly in symbiosis with plants, forming arbuscular mycorrhizae. Mycorrhizae are fungi that live and live in symbiosis on the roots of higher plants. Mycorrhizae form specialized hyphae that grow to form a mycelium that surrounds the tip of the root. Several types of agricultural crops depend on mycorrhizae to grow optimally.
Glomeromycota Characteristics
Fungi that are included in the Glomeromycota division have general and specific characteristics or characteristics that distinguish them from other functional divisions. The general characteristics and specific characteristics of Glomeromycota are as follows.
General Characteristics of Glomeromycota
■ Group fungus symbiosis with plants forming arbuscular mycorrhiza (arbuscular is a food exchange between the fungus with the host plant).
■ Obligate BIOTROP (parasitic on living plants).
■ Asexual (spores outside the host).
■ Not septate (non-septa).
■ Wall hyphae contain chitin, chitosan and polyglucuronic acid.
■ Generate multinucleate spores are large, thick-walled (chlamydospores).
Characteristics / Specific Glomeromycota
■ vesicles (sacs): early stages of the formation of mycorrhizae.
■ Auxiliary (exterior): mycelia attached to the roots of higher plants.
■ arbuscular: after auxiliary ripe, it will form the arbuscular.
■ Spore: forming chlamydospores (thick-walled) and Zygospora (having locomotor).
Glomeromycota Body Structure
Glomeromycota was originally included in the kingdom Zygomycota, but Walker and Schubler in 2002 separated it into a separate kingdom because there were differences with Zygomycota. Currently, only about 150 species of Glomeromycota have been studied.
There are two types of mycorrhizae, namely as follows.
■ ectomycorrhiza , fungal hyphae do not penetrate into the roots (the cortex) but only up to the epidermis only, examples of fungi associated with the roots of pine.
■ Endomikoriza , fungal hyphae penetrate to the cortex, for example, there is the orchid plants and vegetables such as cabbage and beets.
The hallmark of Glomeromycota is that they always live in symbiosis with plants (cannot live freely), form arbuscular dichotomous branches in plant roots), their hyphae are not insulated, and produce large, thick-walled multinucleate spores. The shape of the arbuscula in Glomeromycota is shown in the following figure.
Arbuscular is a structure that is used as a place of exchange of food between fungi and host plants. Another type forms balloon-like structures on the host roots called vesicles . Arbuscular and vesicles also function as storage sites for fungal metabolism.
How to Reproduction Glomeromycota
Glomeromycota reproduce asexually to form spores. They reproduce asexually by blastic development from the tips of the hyphae to produce large spores (glomerospores; sometimes up to 800 m) inside or outside the root. Glomerospores are enclosed by a multi-layered cell wall that includes many nuclei. If conditions are favorable, the spores germinate to form appressoria on the roots of the host plant and form new mycorrhizae. Sexual reproduction in Glomeromycota is not found. The stages of the spore formation process in Glomeromycota fungi are shown in the following figure.
Examples of Glomeromycota and their Benefits
The following are some examples of fungal species belonging to the division Glomeromycota.
● Glomus mosseae
● Glomus epigaeum
● Glomus claroideum
● Archaeospora leptoticha
● Gigaspora coralloidea
● Gigaspora heterogama
● Sclerocystis
● Acaulospora
● Entrophospora
Arbuscular mycorrhizal fungi (AMF)
Arbuscular mycorrhizal fungi are a form of association between fungi and roots of higher plants, reflecting a mutually beneficial functional interaction between a plant and one or more strains of mycobionts in space and time. Mycorrhizal fungi belong to the endomycorrhizal group.
This type of fungus is characterized by intracellular hyphae, i.e. hyphae that penetrate into the cortex from one cell to another. Between the cells there are convoluted hyphae or branching hyphal structures called arbuscules.
Swellings that form on oval-shaped hyphae are called vesicles. The arbuscula is the site of the exchange of metabolites between fungi and plants. The presence of arbuscules is very important to identify that infection has occurred in plant roots), while vesicles are food storage organs and function as propagules (reproductive organs).
Furthermore, it is said that all endophytes and those belonging to the genera Gigaspora, Scutellospora, Glomus, Sclerocystis and Acaulospora are capable of forming arbuscules.
Vesicles, according to Abbott and Robson (1982), are globose in shape and originate from the inflated internal hyphae of mycorrhizal fungi. Vesicles are found both inside and outside the cortical parenchyma layer. Not all mycorrhizal fungi form vesicles in their host roots, such as Gigaspora and Scutellospora.
There are many opinions about the function of these vesicles, namely as reproductive organs or organs that function as food storage places which are then transported into cells.
The main feature of mycorrhizal arbuscules is the presence of arbuscules within the root cortex. Initially the fungus grows between the cortical cells, then penetrates the host cell wall and develops inside the cell.
Factors Affecting the Presence of AMF Spores
The presence of AMF spores is influenced by several environmental factors such as:
1. Light
Excessive shade, especially for light-loving plants, can reduce root infection and spore production, and the response of plants to mycorrhizal fungi will be reduced. This is due to the inhibition of growth and internal development of hyphae in the roots which results in limited external hyphae development in the rhizosphere.
2. Temperature
Temperature affects the infection, namely the development of spores, penetration of hyphae in root cells and development of the root cortex, besides that temperature also affects resistance and symbiosis. The higher the temperature, the greater the formation of colonization and the increase in spore production.
Schenk and Schroder (1974) states that the best temperature for the development of arbuscular ie at a temperature of 30 ° C but for best mycelial colony is at a temperature of 28 ° C - 34 ° C, while the development of the vesicles at a temperature of 35 o C.
3. Soil water content
Soil water content can have a direct or indirect effect on the infection and growth of mycorrhizal fungi. The direct effect of mycorrhizal plants can improve and increase water absorption capacity.
While the indirect effect due to the presence of external mycelia causes mycorrhizal fungi to be effective in aggregating soil grains, the ability of the soil to absorb water increases. Prolonged saturation of groundwater has the potential to reduce the growth and infection of mycorrhizal fungi due to anaerobic conditions.
Daniels and Trappe (1980) used Glomus epigaeum to be germinated on silty clay at various water contents. Glomus epigaeum was found to germinate best at a water content between field capacity and saturated water content.
4. Soil pH
Mycorrhizal fungi are generally more resistant to changes in soil pH. However, the adaptation of each species of mycorrhizal fungi to soil pH is different, because soil pH affects germination, development and the role of mycorrhizae on plant growth.
The optimum pH for the development of mycorrhizal fungi varies depending on the adaptation of the mycorrhizal fungi to the environment. pH can directly affect the activity of enzymes that play a role in the germination of mycorrhizal fungi spores.
For example, Glomus mosseae usually in alkaline soil can germinate well in water or in soil extract agar at pH 6-9. Gigaspora coralloidea and Gigaspora heterogamous spores of the more acid- fast species germinated well at pH 4-6. Glomus epigaeum germination is better at pH 6-8.
5. Organic ingredients
Organic matter is one of the most important components in soil besides water and air. The number of AMF spores is closely related to the content of organic matter in the soil. The maximum number of spores was found in soils containing 1-2% organic matter while in soils containing less than 0.5% organic matter the spore content was very low.
6. Heavy metals and other elements
The presence of heavy metals in the soil solution can affect the development of mycorrhizae. Some arbuscular mycorrhizal species are known to be able to adapt to zinc (Zn) contaminated soil, but most of the mycorrhizal species are sensitive to high Zn content. In several other studies, it was also known that certain mycorrhizal fungal strains were tolerant to high Mn, Al, and Na content.
Mycorrhizal Benefits
Almost all vascular plants have mycorrhizae. Mycorrhiza means “fungal root” which is a mutualistic association of plant roots with fungi. Zygomycota, Askomycota, and Basidiomycota as well as Glomeromycota all have mycorrhizae. Do you remember what kind of fungus forms mycorrhizae on pine trees?
The expansion of the fungal mycelium that forms mycorrhizae increases the absorption surface of the plant roots. The two partners will exchange minerals sucked by fungi from the soil, and organic substances synthesized by plants.
The pine will get the water and nutrients and the fungus will get the organic matter. Thus, mycorrhizae are very important for natural and agricultural ecosystems.
