This presentation offers a bird's eye view of mycorrhizal association with plants along with its role in the growth and development of plants.

1. MYCORRHIZAL
ASSOCIATION
By
Dr. N. Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini College,
Purulia,
D.B. Road, Purulia
(W.B) India

2.  Mycorrhizal association,
 Types of Mycorrhizal association,
 Taxonomy, Occurrence & distribution,
 Phosphorus nutrition,
 Growth & yield,
 Colonization of VAM,
 Isolation & Inoculation Production of VAM,
 VAM-Influence on Plant’s Growth & Productivity,
 References

3.  The terms symbiotic and mutualistic have been used interchangeably to
describe mycorrhizal associations and parasitic fungi have also been called
symbiotic, but many scientists now only call beneficial associations
symbiotic (Lewis 1985, Paracer & Ahmadjian 2000). Symbiosis is defined
broadly as “two or more organisms living together” and in most cases both
partners benefit (Lewis 1985).
 There are many types of symbiosis evolving different combinations of
plants, fungi, microbes and animals. Only plant-fungus associations are
considered in detail here, but several others are illustrated below.
 Fungal symbiosis have been defined as “all associations where fungi come
into contact with living host from which they obtain, in a variety of ways,
either metabolites or nutrients” (Cook 1977).
 However, this definition excludes mycorrhizal associations of myco-
heterotrophic plants, where plants are nutritionally dependant on fungi
(Brundrett 2004). Only the broadest definition of symbiosis - “living
together of two or more organisms”, applies universally to mycorrhizal
associations (Lewis 1985, Smith & Read 1997, Brundrett 2004).

4.  The name mycorrhizas, which literally means fungus-root, was invented by
Frank (1885) for non-pathogenic symbiotic associations between roots and
fungi. A revised definition that includes non-mutualistic mycorrhizas and
excludes other plant-fungus associations is provided below (Brundrett
2004).
 Mycorrhizas are symbiotic associations essential for one or both partners,
between a fungus (specialized for life in soils and plants) and a root (or
other substrate-contacting organ) of a living plant, that is primarily
responsible for nutrient transfer. Mycorrhizas occur in a specialized plant
organ where intimate contact results from synchronized plant-fungus
development.

5.  The structure and development of mycorrhizal fungus hyphae is
substantially altered in the presence of roots of host plants. These root-
borne hyphae are distinct from hyphae which are specialised for growth
in soil.
 All mycorrhizas have intimate contact between hyphae and plant cells
in an interface where nutrient exchange occurs.
 The primary role of mycorrhizas is the transfer of mineral nutrients
from fungus to plant. In most cases there also is substantial transfer of
metabolites from the plant to fungus.
 Mycorrhizas require synchronized plant-fungus development, since
hyphae only colonize young roots (except orchid mycorrhizas and
exploitative VAM).
 Plants control the intensity of mycorrhizas by root growth, digestion of
old interface hyphae in plant cells (AM, orchid), or altered root system
form (ECM).
 Roots evolved as habitats for mycorrhizal fungi. Mycorrhizas normally
occur in roots, but can be hosted in stems in some cases (e.g. some
orchids).

6.  According to Brundrett (2004), the mycorrhizal association can be
categorized as follows:
 A. Arbuscular mycorrhizas:
 It is also known as Arbuscular Mycorrhiza(AM) or Vesicular Arbuscular
Mycorrhizae ( VAM) Consists of Linear VAM, Coiling VAM, Beaded
VAM, Inner Cortex VAM, Exploitative VAM . Here, the fungi belongs to
Glomeromycota and the hosts plants are of diverse types comprising of
woody plants to achlorophyllous plants (Exploitative VAM) .
 Ecto-mycorrhiza: It comprises of Cortical, Epidermal, transfer cells,
Monotropoid, Arbutoid,
 Ecto-endomycorrhizae- Found to occur in the members of Ericaceae like
Arbutus sp and Arcotostaphylos sp, called Arbutoid, shares the features of
both ecto and endo-mycorrhizae ; henceforth known as ecto-endo
mycorhizae; no hertig net formed, stele comprises the mycelia growth.

8.  Orchidaceous mycorrhiza-Orchid being small with scanty reserve food for
the germination of seeds; henceforth the fungi retain within the seeds
supply extra carbon source during the growth of the germination Orchid
seeds. Some of the mycorrhizae are Rhizoctonia, Corticum etc belongs to
Orchidaceous mycorrhizae.
 Ericoid mycorrhizae- Belongs to find in the members of Ericaceae like
Erica, Calluna, Vaccinium etc ,
Mycelia septate and remain within the stele of the host plants,
Members of Ericaceous grow in slight acidic soil with little P & N,
The fungi get carbon source from the host plants and supply N & P to the
host plant in return.
Monotropoid Mycorrhizae-Found in Monotropa hypopitys ,
achlorophyllatous plant root,
Fungi develop mycorrhizae on Pinus and Monotropa sp;
From Pinus, the fungi collect nutrients and supply to Monotropa making a
good relationship in between two plants.

9.  Gentianoid mycorrhizae- Found to occur in the members of Gentianaceae
like Blackstonia perfoliata, Gentianella amarella etc,
The mycorrhizae grow in the roots of the plants,
It develops the mass of the mycelia in the cortex and form vesicles .
Ophloglossoid mycorrhizae- Found to occur in the pteridophytes like
Ophioglossum,
It develops two to three layers of mass of mycelia outside the cortical
layers,
Pyrolaceous mycorrhizae- Found to occur in Pyrola rotundifolia, plant of
Ericaceae family,
Found the small roots of the host plant,
The hyphae consists of dolipore septum with clump connection,
The mycelia form hertig net inside the host plant root structure.

10. Sr.
No
Name Family Ectomycorrhizae Endoimycorrhizae
1. Acacia catechu Mimosaceae +
2. Aegle marmelos Rutaceae +
3. Albezzia lebbeck Mimosaceae +
4. Artocarpus intergrfolia Moraceae +
5. Adhatoda vesica Acanthaceae - -
6. Brassica campestris Brassicaceae - -
7. Coffea arabica Rubiaceae +
8. Curcuma longa Zingiberacea
e
+
9. Eucalyptus globosus Myrtaceae +
10. Ficus benghalensis Moraceae +
11. Lycopersicon esculentum Solanaceae +
12. Zingiber officinale Zingiberacea +

11.  Mycorrhizosphere (the close vicinity of ectomycorrhizae) shows increased
microbial community leading to mycorhizosphere effect. The
photosynthates flow into soil through roots and mycorrhizae support a
diverse community of soil microorganisms, many of which influence plant
growth.
 The mycorrhizosphere microorganisms may be facultative anaerobes,
extracellular chitinase producers, phosphate solubilizers, and producers of
siderophores, antibiotics, hormones, plant growth-suppressors and
promoters.
 Mycorrhizae increase the absorptive surface of root resulting in increased
uptake of water and nutrients from the soil. The ectomycorrhizal fungi
translocate phosphorus, nitrogen, calcium and amino acids, and increase
translocation of Zn, Na and other minerals to the hosts.
 Their hyphae extract N and transport from soil to plant due to increased
absorptive surface area. Plant available phosphorus in soil is in small
amount (1-15%) of total P content. The by-products of fungi dissolve
several insoluble nutrients.

12.  The interaction of mycorrhizal fungi and phosphate solubilizing bacteria,
 (b) Production of phosphatases by the mycorrhizal fungi, and
 (c) Production of organic acids by mycorrhizal fungi.
 Translocation of P in fungal hyphae takes place by cytoplasmic streaming.
P is stored in the form of polyphosphates due to polyphosphate kinase
activity. Then P is transferred to host plant after break down of phosphates
by Polyphosphatases, DES ATPase & Polyphosphate kinase and release of
inorganic phosphate. P is accumulated in mantle and Hartig net and,
thereafter, transferred from Hartig net to host tissue.
 Similarly, the VAM fungi also influence growth, exudation and nutrient
uptake in host plants. Polyphosphate granules have been found in
arbuscules, hyphae and vesicles of VAM fungi. Chitin appears to be the
main carbohydrate-related material present in vesicle and hyphal walls.
Glomus fasciculatus translocate P over a distance of at least 7 cm, and
Rhizopogon luteus to 12 cm.

13.  Mycorrhizae plays a very significant role in the physiological activity of
the plants reflected in terms of growth & yield.
 In tomato, leaf area increases and dry weight of leaves increase 4 times by
the mycorrhizal association,
 In Trifloium repens ( clover), the content of phosphorus increases along
with the dry weight of stem & leaves due to mycorrhizal inoculation,
 In Medicago sativa, biomass increases 170 times due to mycorrhizal
inoculation,
 In legume plants, the number of Rhizobium increases (PGPR) and the
plants can absorb more nitrogen from the vicinity,
 In Orchid, the mycorrhizal inoculation enhances seed germination.
 In Soybean, the growth increases 122% and in Peach, it increases 80%,
 In Foenicum vulgare, the essential oil yield increases 78% after the
inoculation with mycorrhizae,
 In addition to that, It offer multiple benefits like pathogen resistance,
phyto-hormone production , releases immobile nutrients etc as a part of the
mycorrhizal association.

14.  VAM- the kind of endomycorrhiza generally enters into the root of the
members of Endogonaceae like Glomus, Gigaspora by forming vesicles.
Being obligate symbionts, it very difficult to develop pure culture without
host. The following steps are followed for isolation and inoculation.
 ISOLATION
 VAM consisting the roots of the host plants are collected,
 Repeated washed and the roots cut up to 1 cm,
 Washed with 10% KOH , autoclaved and treated with 5% HCl for
neutralization,
 VAM stained with lacto phenol & cotton blue and observed under
compound microscope,
 VAM mainly identified with presence of azygospore and chlamydospores,
 Species are identified with proper references

15.  INOCULATION
 VAM is taken along with the root,
 The root is undergone sterilization and with proper solution, tit develops
lateral growth of the root,
 From the lateral branch, the spores are separated and allow to undergo
germination; if the spores do not germinate within 10 days, it is thought
that the spores have undergone degeneration,
 If it is not possible to cause infection with the desired roots, the spores are
kept at 4 ℃ temperature either in cold water or 0.4% Gellan gum & 0.1%
MgSO4, 7H2O solution,
 Within 2-15 days, the fresh roots are inoculated in presence of U-V
exposure.

16.  Strengthen the root system and increases water absorption
 Develop resistance against the soil borne pathogens,
 Qualitative and quantitative yield of the plants,
 The aggregation of soil particles enables to form soil And reduce soil
erosion,
 The VAM inoculated plants increases defence mechanisms against the
pathogens,
 To increase the absorption of water and nutrients,
 To develop resistance heavy metals and salt tolerance,
 To increase the absorption of P, N, Zn and other minerals,
 VAM becomes function in the vicinity of rhizospheres. Hence it is used as
bio-fertlizer in the crop fields,
 Due to use of VAM, the nitrogen fixing bacteria, Rhizobium becomes
increase that enable the soil fertility by natural process and reduce to
chance of the pathogens around the rhizospheres,
 VAM can be used as nutritional supplements for the standing crops.

17.  References:
 1. Fundamental Botany- Sen & Giri
 2. A text of Fungi- Vasistha,
 3. A Textbook of Microbiology- R.P. Singh,
 4.Textbook of Microbiology- Dubey & Maheswari
 5. Soil Microbiology- N.S. Subba Rao
 6. Agricultural Microbiology- G. Rangaswami
 7. Google for images
 8. Different WebPages for information.
 Disclaimer: This PPT has been made to enrich free online study
resources without any pleasure of financial interest.