Definition

• These are the fungi which form ectomycorrhizal association with plants and Ectomycorrhizal associations (abbreviated as ECM, or EM) are mutualistic associations between higher fungi and Gymnosperms or Angiosperms. ECM associations consist of a soil mycelium system, linking mycorrhizal roots and storage or reproductive structures. Ectomycorrhizal roots (formerly known as ectotrophic or sheathing mycorrhizas) are characterized by the presence of a mantle and Hartig net.

Structural Diversity

Structural Diversity

• Many ECM fungi have mushroom-like fruit bodies with gills, tubes, teeth, etc. arising from soil, but there are also many saprophytes in most of these categories.

• The majority of subterranean fungi (called truffles or truffle-like) are considered to be ECM associates, but some probably are not.

Structural Diversity

• Fungi fruiting on wood are usually not mycorrhizal, with the exception of some crust fungi.

• Root system

• Soil hyphae

• Root contact & hyphal proliferation

• Mycorrhizal roots

• Harting net

• Reproduction

• Most ECM roots have a modified lateral rootbranching pattern. This pattern, which is called heterorhizy, consists of short mycorrhizal lateral roots (called short roots) supported by a network of long roots.

• Mycorrhizal fungi produce a hyphal network in soil consisting of individual strands of hyphae and/or relatively undifferentiated bundles of hyphae called mycelial strands, or rhizomorphs with specialized conducting hyphae.

• Sclerotia, which are larger, resistant storage structures, may also be produced.

• Soil hyphae function by acquiring nutrients re-allocating resources for fungus reproduction or mycorrhizal exchange and by functioning as propagules for survival and spread of the fungus.

Root Contact and Hyphal Proliferation

• Hyphae contact, recognise and adhere to root epidermal cells near the apex of young, actively growing, high-order, lateral root. These laterals are called short roots because they normally have restricted growth

Mycorrhizal roots

• After ECM associations are established, mycorrhizal short roots often continue to grow by elongation and branching.

• Conifer roots with ECM have dichotomous branching patterns, while angiosperms have sympodial branching.

Mycorrhizal roots

The Hartig Net

• Hyphae penetrate between host cells and branch to form a labyrinthine structure called the Hartig net.

• Host responses may include polyphenol production in cells and the deposition of secondary metabolites in walls .

The Hartig Net

• Angiosperms with ECM, such as Eucalyptus, Betula, Populus, Fagus, Shorea, etc., usually have a one cell layer Hartig net confined to the epidermis. This is the epidermal category of ECM

• In gymnosperms such as Pinus, where Hartig net hyphae extend deep into the cortex. This is the cortical category of ECM.

Reproduction

• The hyphal network that interconnects ECM fungi in soils is also responsible for reproduction. Fruit bodies grow from primordia at times of the year when environmental conditions are favorable. Some fungi will fruit under mycorrhizal plants growing in pots, as shown below.

Fruit bodies of an ECM fungus (Laccaria sp.) under a Eucalyptus globulus seedling inoculated with fungal mycelia

Anatomical terms of ECM fungi

• Mantle

• Hartig net

• Heterorhizy

• Short roots

• Long roots

• Dichotomous branching

• Pinnate branching

• Soil hyphae

Anatomical terms of ECM fungi

• Mycelial strands

• Rhizomorphs

• Fruit bodies

• Sclerotia

Host plants

• Dominant in coniferous forests

• Cold boreal or alpine regions,

• Broad-leaved forests in temperate or Mediterranean regions,

• Some in tropical or subtropical savanna or rain forests habitats

• Ectomycorrhizal associations can improve the phosphate status of plants in soils that are phosphate deficient.

• Enhance nitrogen nutrition of plants where nitrogen is deficient.

• Ectomycorrhizal fungi helps plants avoid disease and survive periods of drought.

• The size, color, texture and branching patterns of ECM roots vary with different host-fungus combinations, which are called morphotypes.

Ectomycorrhizal morphotype

ECM fungi of Pakistan

• Cantharellus cibarius is associated with Pinuswallichiana.

• Tricholoma aurantium is associated with Abies pindrow.

• Suillus brevipes is associated with Querus incana.

• Suillus sibiricus is associated with pinus wallichiana.

• Russula livescens, Peziza and 3 species of Tomentella are associated with Cedrusdeodara.

• Lactarius sanguifluus is associated with Quercus incana, and Populus