Glomus macrocarpum Tul. & Tul. is a vesicular-arbuscular endomycorrhizal fungi found in the family Glomeraceae. This species was first loosely defined by Tulasne and Tulasne in Nuovo Giornale Botanico Italiano in 1845, who then further described the species and included line drawings in Fungí Hypogaei in 1851 (Berch and Fortin 1983). These samples were collected from Chinon, within the French province of Touraine, one sample of which was used as a lectotype of the species by Berch and Fortin (1983). This lectotypification narrowed the synonyms to Glomus macrocarpus Tul. &Tul., Endogone macrocarpa (Tul. & Tul.) Tul. & Tul., Endogone guttulata Fischer, and Endogone nuda Petch. Gerdemann and Trappe (1974) suggested two varieties within the species: var. macrocarpus and var. geosporus, however var. geosporus has since been reclassified as Funnelformis geosporum (Schüßler and Walker 2010).
G. macrocarpum is located in kingdom Fungi, phylum Glomeromycota, order Glomerales, and family Glomeraceae. Molecular phylogeny of Glomeromycota has been conducted using the small subunit rRNA gene and the internal transcribed spacer region, placing Glomeromycota as a monophyletic phylum that diverged from the Dikarya approximately 600 million years ago (Schüßler et al 2011). G. macrocarpum is most closely related to an unknown Glomus sp. and the most closely related genus is Funneliformis (Krüger et al 2012), which are characterized by funnel-shaped spore formation (Schüßler and Walker 2010).
Spores of Glomus macrocarpum are either globose or sub-globose with “two distinct wall layers” (Berch and Fortin 1983). They are found as individuals or “loose aggregates” and have “smooth plate-like structures” on their exterior (Tewari et al. 1982). These layers are believed to aid in retaining moisture as well as potentially preventing parasitism.
Godfrey (1957) defined four different types of sporocarps exist in this species with variable morphological characteristics, defined by spore color: golden, yellow, brown, and orange. Golden spored sporocarps have “erect branched hyphae bearing spores” on their surface with thickened hyphal walls, with spores 130-160 µm diameter with a cell wall 4-6 µm thick. The surface of yellow spored types have a “flattened covering of undifferentiated hyphae” that also have thickened hyphal walls. These spores are 130-160 µm in diameter with spore walls 7-10 µm thick. Sporocarps of brown and orange spored types have “well differentiated hairs” on their surface, brown and yellow in color respectively, forming a “more or less developed peridium” that lack thickened hyphal walls. Brown spores are 180-200 µm in diameter with walls 10 µm thick, whereas orange spores are 133-175 µm with walls 4-5 µm thick. The sporocarps can be up to 12 mm in diameter and are regularly covered in soil and have a “white and cottony” peridium that may be absent (Gerdemann and Trappe 1974).
G. macrocarpum has a broad distribution, and has been found in France (Tulasne and Tulasne 1851), Poland (Blaszkowski 1994), Britain (Godfrey 1957), the former U.S.S.R. (Berch and Fortin 1983), Australia (Tandy 1975), and throughout the US; including Florida (Nicolson and Schenck 1979), Maine, and California (Berch and Fortin 1983). This species can be found in many different habitats, from coastal to montane regions in “forests…meadows, fields, orchards and greenhouses” (Gerdemann and Trappe 1974).
Glomus macrocarpum is an arbuscular mycorrhizal fungi, making it an obligate symbiont that can only survive in plant roots. As in other arbuscular mycorrhizal fungi, G. macrocarpum forms a mutualistic relationship with its host plant by improving uptake of nutrients from the soil and receiving carbohydrates produced by the host (Schüßler et al. 2001). Ho and Trappe (1975) found that this species has the ability to reduce nitrate to nitrite, thought to be a means of efficiently delivering nitrogen to its host.
Two hyperparasitic fungi have been observed consuming G. macrocarpum chlamydospores, one of which was a Phlyctochytrium which cover the surface of chlamydospores with spores and sporangia. The second parasite was an unidentified Pythium-like fungus that consumed the interior of the chlamydospores, producing its own spores within (Ross and Ruttencutter 1976). Chlamydospores of this species are dispersed by mycophagy, and have been found in the feces of Oregon vole (Trappe and Maser 1976). G macrocarpum is pathogenic to tobacco (Modjo and Hendrix 1986), but tend to form mutualistic relationships with many other plants such as Acer, Sequoia, and Prunus (Gerdemann and Trappe 1974).
Glomus macrocarpum causes tobacco stunt disease. Colonization of tobacco roots causes stunted shoot and root growth and can reduce yields by up to 50% (Hendrix and Csinos 1985). Crop rotation with fescue is an effective cultural means of preventing tobacco stunt (Guo et al. 1994). Kesba and Al-Sayed (2005) found that G. macrocarpum has adverse effects on nematodes parasitizing grape, reducing galls formed and restricting populations by up to 40-50%. This species has been observed in the rhizosphere soil of soybean, grape, and citrus in Florida, though no studies have determined if there is any direct benefit to the production of these crops (Nicolson and Schenck 1979).
Glomus macrocarpum is a vesicular-arbuscular endomycorrhizal plant pathogen in the Glomeraceae family of fungi. Also occasionally known as Endogone macrocarpa, G. macrocarpum is pathogenic to multiple plants, including tobacco and chili plants. G. macrocarpum was first discovered in the French woodlands by the Tulsane brothers in the early to mid 1800s.[1] Their first known description of G. macrocarpum was published in the New Italian Botanical Journal in 1845.[1] G. macrocarpum has since been documented in over 26 countries, including Australia, China, and Japan for example. G. macrocarpum is frequently found in grassy meadows, forests, greenhouses, and fruit orchards. It is known for its small, round-edged, and light brown to yellow-brown sporocarp. G. macrocarpum is sometimes known as the “Glomerales truffle".[1]
The sporocarp of G. macrocarpum is small, usually measuring up to about 12 millimeters in diameter. The sporocarp shape ranges from globose, subglobose, elongate, to irregular. The sporocarp is also often observed to have soil (primary substrate) embedded in its surface. When the peridium is present, it appears white with a cottony texture.[2] The sporocarp color ranges from yellow-brown to light brown.
Chlamydospores that act as resting spores or survival structures are present. These allow the fungus to remain dormant during inadequate germination conditions. Once appropriate germination conditions are reached, chlamydospores form germ tubes to germinate into hyphal structures that place pressure on plant surfaces in order to infiltrate various tissues and begin forming a mycorrhizal association. Chlamydospores are globose to ellipsoid, and aseptate.[2] Spores range in size from about 100 to 350 μm in diameter. Spore walls are yellow to brown in color.[3] Spores arise from subtending hyphae that range from 12 to 25 μm in width. Hyphae are also cylindrical and lacking in pigmentation. Both young and mature spores are often evident on the sporocarp surface. The sporocarp of G. macrocarpum is a relatively fragile structure with other environmental components, such as soil, sometimes embedded in its surface.[2]
Ultrastructural studies indicate that two wall layers, containing fibrils, are present in spores. There is a slight separation zone present between the two wall layers. Spore contents are also indicated to be lipid globules from subtending hyphae as an energy source for the spores.[4]
Glomus macrocarpum is a vesicular-arbuscular mycorrhizal fungus that forms associations with many different plant types. The fungus grows in a hypogeous manner, just underneath the topsoil in various geographical locations and environments.[1] The fruiting season of G. macrocarpum occurs during the summer and fall months.[2] Until relatively recently, Glomus species were thought to be exclusively asexual organisms. However, studies have been conducted to analyze the presence of sex-pheromone sensing proteins in some Glomus species. The presence of these sensing proteins is indicative that species in this genus may not be entirely asexual. However, the validity of a sexual process in Glomus species has not been confirmed.[5]
Laboratory studies of G. macrocarpum indicate that the species has both positive and negative effects on a variety of plant species, many of which are of economic importance worldwide.[6][7]
Glomus macrocarpum spores have been studied and subjected to autoclaving or ethanol treatment in order to measure the ability of spores to survive under these conditions. Spores that were treated were sourced either from fresh pot cultures or from cultures stored for five years. Spores were treated with MTT stain, which causes living spores to appear red and non-living spores to appear black or dark blue. After treatment, the percentage of living spores was measured at 10, 20, 30, 40, and 72 hours. Results indicated that spores sourced from fresh pot cultures had a higher survival rate after treatment than those sourced from five year old cultures.[8] Results also indicated that after 72 hours most spores that were stained red (living) from 40 to 72 hours had turned black or dark blue and were no longer viable.[8] Since G. macrocarpum can be pathogenic and often remains in areas for a long period of time after sporocarp removal, researchers are attempting to understand the effect that time, combined with other treatments, has on spore viability.
Glomus macrocarpum was discovered to be a strong factor in improving essential oil quality and concentration in dill and carum plants.[6] Both of these plants are used commonly as spices, and essential oil quality and concentration is an important part of what allows plants to be used as spices. Glomus macrocarpum was found to be more effective than other Glomus species at enhancing essential oil concentrations. Analyzed plants were inoculated with G. macrocarpum inoculated soil and the essential oils in the plants were analyzed after 15 weeks, allowing for the Glomus species to form mycorrhizal associations effectively.[6] Studies found that there was a significant increase in biomass due to the mycorrhizal association with G. macrocarpum. Host plants inoculated with G. macrocarpum were observed to have higher shoot growth than that of the control group after 15 weeks.[6]
Glomus macrocarpum is one fungal species among many whose ability to enhance plant uptake of nutrients is being studied. Worldwide, crops are grown using chemical fertilizers enriched with the required nutrients for plant growth. However, this practice has proven to be unsustainable due to worsening water quality in places where these chemical fertilizers are heavily relied on. G. macrocarpum and others are being considered as a way to lessen the amount of chemical fertilizers necessary for producing crops of economic importance.
Spore production of G. macrocarpum is influenced by a variety of host plants. Studies have shown that G. macrocarpum spore production significantly increases with bahiagrass as a plant host when compared to corn or sudangrass as plant hosts. Studies indicate that G. macrocarpum spore production will change significantly after at least 14 weeks after planting inoculated host plants.[9]
Glomus species are found in nearly all terrestrial habitats including arable land, deserts, grasslands, tropical forests, mesic forests, and deciduous forests. G. macrocarpum has been identified in over 26 countries in different climates throughout the world, including: Australia, Austria, Belgium, Brazil, Canada, China, Denmark, France, Germany, Hungary, Ireland, Italy, Romania, Sweden, and the United States of America.[6][10][11]
Glomus macrocarpum is a vesicular-arbuscular endomycorrhizal plant pathogen in the Glomeraceae family of fungi. Also occasionally known as Endogone macrocarpa, G. macrocarpum is pathogenic to multiple plants, including tobacco and chili plants. G. macrocarpum was first discovered in the French woodlands by the Tulsane brothers in the early to mid 1800s. Their first known description of G. macrocarpum was published in the New Italian Botanical Journal in 1845. G. macrocarpum has since been documented in over 26 countries, including Australia, China, and Japan for example. G. macrocarpum is frequently found in grassy meadows, forests, greenhouses, and fruit orchards. It is known for its small, round-edged, and light brown to yellow-brown sporocarp. G. macrocarpum is sometimes known as the “Glomerales truffle".
