3. Mycorrhizae
0 The most prevalent beneficial organisms associated with
plants, however, are soil-inhabiting fungi that form mutualistic
root–fungal associations referred to as mycorrhizas
0 All mycorrhizas have intimate contact between hyphae and
plant cells in an interface where nutrient exchange occurs.
0 Majority of plants form mycorrhizas, it is likely to lie
somewhere between 80% and 90%. In many of these
associations between 10% and 30% of the food produced by the
plant moves through to the fungi.
4. Mycorrhizae
0 Mycorrhizas are found in a wide range of habitats,
including deserts, lowland tropical rainforests, high
latitudes and altitudes
0 Uptake of nutrient and Mineral nutrient acquisition from
soil is considered to be the primary function of
mycorrhizas, in addition to it’s roles in ecology, and man
economic uses..
5. The pioneering work of Frank , resulted in the
recognition of
two broad subdivisions of mycorrhizas,
Ectomycorrhizas and Endomycorrhizas
6. Mycorrhizae Types
Two major types of mycorrhiza occur in Nature
Endomycorrhiza “vesicullar-arbuscular”
(common in more than 80 % of terrestrial plant
species)
Ectomycorrhiza (specific to conifers and some
broadleaved woody species) %15 of plants
There exists other types: Ericoid, Orchid,
monotropoid mycorrhiza of less ecological
importance.
7. Ectomycorrhiza
The formation of a mantle or sheath of
hyphae that covers considerable
portions of lateral roots, the
development of hyphae between root
cells form a complex highly branched
structure called the Hartig net,
Ectomycorrhiza: root tip of
Pinus nigra colonised by
ectomycorrhizal fungus
8. Ectomycorrhiza
Ectomycorrhizas are usually
found on tree species
although a few shrub and
herbaceous species may also
develop this association. A
detailed list of the conifer
and angiosperm families.
*Fungi groups with
large fruiting bodies, e.g.
mushrooms,
truffles and puffballs.
9. Ectomycorrhizas can
also confer pathogen
resistance to their
plant partner, and
they are more
effective at this,
compared to AM
roots
10. It has been estimated that between 5,000 and 6,000
species of fungi form ecto- or ectendo-mycorrhizas.
Around 4,500 of these are epigeous (have above-ground
fruiting bodies), but up a quarter are hypogeous (with
underground fruiting bodies) such as truffles
White Truffles (Tuber magnatum). Fly agaric (Amanita
muscaria).
11. Endomycorrhiza
They are either Vesicular or
Arbuscular;
Consists of hyphae that
meander between the cortex
cells, and often enter them.
Vesicular-arbuscular mycorrhiza: Highly
colonized root of maize dyed with trypan
blue. Mycorrhizal formations are clearly
visible: 1) vesicles; 2) arbuscules
12. Main cellular features of the arbuscular endomycorrhiza
Hyphae from a germinating spore infect a root hair and can grow
within the root between root cortical cells and also penetrate individual
cells, forming arbuscules. These are finely branched clusters of hyphae,
which are thought to be the major site of nutrient exchange between
fungus and plant.
14. •Arbuscules: transfer organs
of the mycorrhizae.
•Hyphae: connect root to
soil. Act as pipeline
•Spores: resting,
lipid filled structures.
Is the seed
of the fungus world.
•Identification
is based on these.
15. Many common desert plants, including cacti, are heavily
mycorrhizal.. indicating that mycorrhizas have a particularly
important role in water relations in dry ecosystems and in soils
with poor water retention
16. 0 Mycorrhizas increase nutrient uptake from the soil.
0 Mycorrhizal fungi can be used in the biocontrol of
pathogenic fungi and nematodes.
0 Some mycorrhizal fungi can bind heavy metals thus
protecting plants from toxic levels of these substances.
0 Mycorrhizas have a positive effect on the establishment of
plant communities.
17. If no other factors
are limiting, growth
will be proportional
to the amount of P
absorbed by plants.
Mycorrhizae may
supply up to 80%*
of the plant P.
18. Agricultural
advantages
• Allow plants to draw more
nutrients and water from the soil,
including phosphorus
• Result in vigorous and healthy
plants
• Accelerate rooting
• Increase plant survival
• Increase drought tolerance and
others stresses
• Enhance flowering and fruiting
19. Ecological Importance
0 Improvement of soil structure • Stimulation of
beneficial microbial activity
0 Water infiltration improvement • Reduction of erosion
and nutrient leaching
20. 0 AM ; also contribute to microaggregate formation in soils
due to the production of a glycoprotein called “glomalin”;
glycoprotein that acts as a glue for soil structure.
0 Aggregate formation reduces decomposition of SOM,
maintaining C in the soil. SOM also holds water and retains
nutrients.
Most of the research on the interactions between plants, the environment, and other organismshas involved those parts of plants that are visible and easy to access. However, the undergroundsystem, mainly roots, interacts with the soil environment and with a multitude of organisms invery complex ways. The interaction of roots with mycorrhizal fungi is almost ubiquitous in bothnatural and man-made ecosystems. Because of this, there are a number of
While the classical Greek word for mushroom is part of the word mycorrhiza, there are many mycorrhizal fungi which have fruiting bodies other than mushrooms. An example is Hydnumrepandum . It’s superficially mushroom-like (stem and cap), but below the cap there are spines rather than gills. There’s more about the fruiting bodies of mycorrhizal fungi later on
Arbuscularmycorrhiza is the dominant type in the tropics, and in grasslands and deserts of temperate latitudes. Ectomycorrhizas predominate in temperate and boreal forests
Ectomycorrhizas are characterized by theformation of a mantle and a Hartig net of intercellularhyphae on roots of predominantly treespecies. Endomycorrhizas are more variable thanectomycorrhizas in that herbaceous and treespecies are involved and there is a diversity of fungalgroups involved in forming these associations.Endomycorrhizas have, therefore, been furtherclassified as either arbuscularmycorrhizas, ericoidmycorrhizas, arbutoidmycorrhizas, monotropoidmycorrhizas, ectendomycorrhizas or orchid mycorrhizas.Each of these categories is characterizedby the invasion of root cells by fungal hyphae butprofound differences occur in the nature of intracellularhypha development.
Compared to arbuscularmycorrhizas (AM), the range of plants colonised by ectomycorrhizas (ECM) is relatively small
Someectomycorrhizas develop linear aggregations ofhyphae (rhizomorphs or strands), in the extraradicalmycelium that are specialized for rapid transport ofnutrients and water. A few ectomycorrhizal fungidevelop sclerotia consisting of compact storagehyphae surrounded by a rind. Hypogeous or epigeousreproductive bodies may also be formed periodicallyfrom extraradical mycelium.
Fungal species involved ; Approximately 5,500 known species of fungi are able to form ectomycorrhizas,,The majority of fungal species involved in the ectomycorrhiza symbiosis belong to families in the Basidiomycotina (basidiomycetes), with a few species belonging to the Ascomycotina(ascomycetes).
•excretion of antifungal and antibiotic substances - 80% of Trichloma spp. produce antibiotics and Boletus and Clitocybe produce antimycotic substances;•stimulation of other microorganism, which themselves limit pathogens;•production of antibiotics by the plant, under the control of the mycorrhizal fungi;•structural protection of the root by the thick fungal coat, the mechanical barrier of the sheath gives very effective protection, since pathogens attack plant tissue and cannot infect fungal tissue.
Besides intraradical structures, AM fungi form also an extensive network of extraradical mycelium in soil that extends into bulk soil beyond the rhizosphere and enables the host plant to absorb nutrients, particularly relatively immobile phosphorus, from a considerably larger volume of the soil. By the differentiation of vegetative hyphae, AM reproductive structures - spores of different size, texture and colour (depending on the species) are formed asexually on extraradical mycelium in soil.
All AM fungi are obligatelybiotrophic, as they are completely dependent on plants for their survival. This is not usually a problem for AM fungi, as they show little or no host specificity
Short-life arbuscules with their main trunk and fine branches resembling small trees serve as a site of the intensive nutrient exchange between plant and fungus. In contrast, vesicles, i.e. globose or oval swellings formed terminally or intercalarly on intraradical hyphae, have a storage function.
Generally fungi have in its cell wall structure chitin that is responsible for the adsorption of the heavy metals like Cd, Ni, Th and Ur
Recent researchindicates that the fungi even help break down rock, increasing availability of the essentialnutrients within, such as potassium, calcium, zinc and magnesium.
The fungal sheath can also aid plants growing in soils with high concentrations of heavy metals. Zinc, cadmium and arsenic have both been found in high concentrations in fungal sheaths and it is thought that certain mycorrhizal isolates accumulate and immobilise heavy metals in hyphae of their fungal sheaths. In this way, metals are unable to reach plant tissues and the plant remains undamaged.
