The Name
The words mycorrhizal, mycorrhiza, and mycorrhizae are often used improperly. Many product labels, and even some published research, use the terms interchangeably and incorrectly. Here’s how to use the terms correctly:
- Mycorrhizal is the adjective used to describe the fungus or fungi, as in mycorrhizal fungi. The term has nothing to do with roots or the relationship of fungus to root.
- Mycorrhiza is the singular noun used to describe the partnership of root and mycorrhizal fungus. The term always refers to the root and the fungus together.
- Mycorrhizae is the plural form of mycorrhiza. The term refers to relationships, associations, partnerships—between and consisting of both fungi and roots.
What are Mycorrhizal Fungi
WHO NEEDS MYCORRHIZAE?MYCORRHIZAL FUNGI HAVE existed and supported plants since terrestrial plants evolved more than 450 million years ago. In fact, mycorrhizal associations are believed to be a major factor that enabled plants to survive on land. The earliest fossil records of plant roots contain arbuscular mycorrhizae that look almost identical to arbuscular mycorrhizae growing in modern soils.
Today we know the true importance of mycorrhizal relationships, and we understand how they operate: the fungus colonizes the root system of a host plant, increasing the roots’ water and nutrient absorption capabilities, while the plant provides the fungus with carbon it obtains from photosynthesis. Both organisms thrive as a result of this symbiotic relationship.
BENEFITS OF MYCORRHIZAL FUNGIWithout mycorrhizal relationships, most plants would probably not exist. Most members of the plant kingdom have formed associations with mycorrhizal fungi, including bryophytes (such as mosses), angiosperms (most land plants), pteridophytes (such as ferns and club mosses), and many gymnosperms (such as conifers). These plant–fungal associations have remained pretty much the same despite all manner of other evolutionary changes that have occurred. Although mycorrhizae are important to most plants, not all plants depend on these relationships to the same degree.Some plants will not survive without mycorrhizal fungi, while a few others do not require mycorrhizae at all.
MYCORRHIZAL TYPESPlants involved in a mycorrhizal relationship are better able to withstand drought and other environmental stresses, root pathogens, and even foliar diseases. Plant biomass is often improved, along with the timing and number of flowers and amount of fruit produced. Mycorrhizae also offer much to the soil by improving structure as the fungal hyphae explore for nutrients.
Mycorrhizae are sensitive to environmental conditions and can behave one way in a study under greenhouse conditions and another way outdoors in the field. To complicate the situation, mycorrhizal fungi can exchange DNA with other microorganisms and shift the benefits they confer. Nevertheless, much scientific research has confirmed the importance of mycorrhizae and the benefits of mycorrhizal associations to plants.
The Benefits
- Increased nutrient supply
- Drought tolerance
- Protection from pathogens
- Improved soil structure and carbon storage
- Protectionism
MYCORRHIZAL PLANT STUDIESMycorrhizal fungi are commonly divided into two groups according to how the fungal cells associate with plant cells. The hyphae of endomycorrhizal fungi penetrate the cell wall, but they do not enter the cell beyond the plasma membrane; these mycorrhizal types are most often associated with the roots of vegetables, grasses, flowers, shrubs, and fruit and ornamental trees. The hyphae of ectomycorrhizal fungi do not penetrate all the way through the cell wall; they form ectomycorrhizae mainly with conifers and some deciduous trees such as oaks.
Endomycorrhizal fungi fall into three main subgroups, each of which has adapted to particular types of host plants, after which the relationship is named: arbuscular, ericoid, and orchid mycorrhizae. Of these, arbuscular mycorrhizae are by far the most common and widespread type. They are of great importance to growers.
ARBUSCULAR MYCORRHIZAE
About 70 percent of all terrestrial plants form the same arbuscular mycorrhizal associations found in fossils from the Devonian period, about 420 million years ago. All arbuscular mycorrhizal fungi are members of the phylum Glomeromycota and form the dominant type of mycorrhizal.
ERICOID MYCORRHIZAE
Ericoid mycorrhizal fungi form mutualistic symbiotic relationships with members of the plant family Ericaceae, which includes rhododendrons and azaleas (Rhododendron spp.) and blueberries and cranberries (Vaccinium spp.). These plants grow in acidic, peat-rich soils and make up about 5 percent of terrestrial plant species. The largest fungal group that enters into these relationships are the ascomycetes, which have adapted to the fine root system of ericaceous plants. These roots have an epidermis and a one- or two-cell–layered cortex. The ericoid mycorrhizal fungal hypha penetrates the cortical cell wall and forms a dense coil structure, or peleton.
ORCHID MYCORRHIZAE
About 10 percent of the Earth’s plant species are orchids (family Orchidaceae), and most of them depend on specialized endomycorrhizal fungi from the Basidiomycota at some point in their lives. Orchid seeds are tiny and do not contain sufficient nutrients to support the growing embryonic plant; they get what they need from the mycorrhizal association.
ARBUTOID MYCORRHIZAE
The fungi that form arbutoid mycorrhizal relationships are the Basidiomycota. The most important host plants in these mycorrhizal relationships are the Pacific Northwest madrone tree (Arbutus menziesii), from which the arbutoid name is derived, and manzanitas and bearberries (Arctostaphylos spp.). In arbutoid mycorrhizal associations, a mantle surrounds the roots of the host plant, and intercellular Hartig nets are formed. Sometimes, however, arbutoid mycorrhizal fungi will penetrate the root’s cell wall, as in endomycorrhizae.
MONOTROPOID MYCORRHIZAE
Monotropoid mycorrhizal fungi were once thought to be part of the arbutoid group, but they do not penetrate the plant cell walls. They colonize plants of the family Monotropaceae, which includes Indian pipes (Monotropa spp.), a woodland plant that lacks chlorophyll. In fact, all plant hosts in this group lack chlorophyll. The fungi form an ectomycorrhizal association with trees such as beech (Fagus spp.), oak (Quercus spp.), and cedar (Cedrus spp.) and then form a monotropoid association and transfer some of the trees’ carbon to the plants.
Monotropoid mycorrhizal fungi form a dense sheath, or mantle, around the root. These fungi also form Hartig nets, which surround but do not penetrate the root cells. Some individual hyphae form fungal pegs, which do penetrate the cortex. These live inside the host plant for a couple of weeks and then die. The host plant absorbs the fungal hyphae after they die to obtain the carbon it needs.
ECTOMYCORRHIZAE
Ectomycorrhizal fungi are more modern than endomycorrhizal fungi. They evolved to associate with plants about 250 million years ago. Although there are several thousand different types of ectomycorrhizal fungi, only about 5 percent of terrestrial plants form ectomycorrhizal associations with ascomycetes or basidiomycetes. In addition, many of these fungi produce mushrooms next to their plant hosts and are not only recognizable but often of economic and culinary value. Ectomycorrhizal fungi are more acidophilic than other mycorrhizal fungi—that is, they prefer acidic soils with a low pH.
ECTENDOMYCORRHIZAE
Though rare, some mycorrhizae have the characteristics of both endo- and ectomycorrhizae. This seems to be confined to a few species of deuteromycetes, which are imperfect fungi. Ectendomycorrhizae form in pot-grown nursery seedlings and with some tree seedlings, mostly pines, after forest fires. The host can be either coniferous or deciduous. A thin mantle is formed, and the hyphae of the Hartig net penetrate the cortex cells but not the plasma membrane. Eventually, these associations morph into ectomycorrhizae as the seedling matures.
SEBACINOID MYCORRHIZAE
A special group of basidiomycetes in the order Sebacinales, the sebacinoids are very diverse in terms of their mycorrhizal relationships. Some form endomycorrhizae while others are ectomycorrhizal in nature, or they form ericoid and even orchid mycorrhizae. Sebacinoid fungi can colonize the tree roots of Eucalyptus marginata, one of the most common species of native eucalyptus in Australia.
Ref: JEFF LOWENFELS - TEAMING WITH FUNGICannabis (Cannabis sativa) Claroideoglomus claroideum, C. etunicatum, Funneliformis geosporum, F. mosseae, Glomus microaggregatum, Rhizophagus clarus, and R. intraradices are successful inoculants for cannabis growing in rockwool. Using mixes of several inoculants results in healthy plants, but studies indicate that inoculating with R. intraradices alone produces similar results.
Maintaining proper temperatures will maximize mycorrhizal colonization. Arbuscular mycorrhizal fungi thrive in temperatures of 65–75°F (24–30°C), which is also the ideal temperature for most plants. Growers should be aware that vesicles, spores, and fungal hyphae will not survive temperatures above 120°F (49°C). Plants would die under such extremely high temperatures as well. When storing mycorrhizal inoculants, growers should also consider appropriate temperature conditions.
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