3. MYCORRHIZA
Plural : mycorrhizas/ mycorrhizae
Symbiotic association between a fungus and the roots of
a vascular plant
Greek words : myker = fungus & rhiza = root
Literally : fungus roots
4. Abundant
Both partners are depends on each other & thus have co-evolved
The fungus role :-
a. plant’s root hairs
b. acts as an extension of the root systems
5. Involve 3- way interactions between host plants,
mutualistic fungi and soil factors
Host
plant
Fungus
Soil
factors
6. Effect of mycorrhizal fungi on their host
Mycorrhizoshpere effect
Nutrient uptake & translocation
Transfer of metabolites from host to fungal symbionts & other
plants
Growth hormone/ antibiotic production
Plant protection/ biocontrol of pathogen
Limit plant species diversity
7. Classification
By Frank on the basis of trophic level
a. Ectotrophic
b. Endotrophic
Based on morphological & anatomical features
a. Ectomycorrhiza (inside feeding)
b. Endomycorrhiza (outside feeding)
c. Ectendomycorrhiza (outside-inside feeding)
8. By Harley & Smith (1983) of endomycorrhiza
a. Vesicular arbuscular (VAM)
b. Arbutoid
c. Monotropoid
d. Ericoid
e. Orchid
Mark identified 7 : VA, AM, ecto-, endo-, ectendo-,
monotropoid, erichoid & orchid mycorrhizae.
9. Initiation of mycorrhiza
Host plant exudates(seedling stage)
Triggers fungal spore germination
Establishment of mycorrhiza
Plant secrete auxins
Branching of infected roots
Fungi withdraw soluble sugars by starch hydrolysis
10.
11. Ectomycorrhizas(ECM)
Most conspicuous, easily recognized & best characterized
Host range: 10% of plant families, mostly woody plants
including the birch, dipterocarp, eucalyptus, oak, pine, rose
families & orchids.
Fungi involved: fungi belonging to the Basidiomycota,
Ascomycota, Zygomycota, imperfecti & occassionally
Phycomycota
Fungal tissue may account for up to 40% mass of root
Hyphae also extend out into the soil – extramatrical hyphae
13. Association development
Growth of fungal mycelium around plant root
Mycelium thickens & form a sheath / mantle covering the entire root
Plants release chemical signals that limit root hair growth
From root surface fungi extend hyphae into the soil
Hyphae aggregate to form ‘rhizomorphs’
Inside the sheath, hyphae penetrate the cortical root cells forming a meshwork of
hyphae/ ‘hartig net’
Soil nutrients – Rhizomorphs – hyphal sheath – hartig net – root cells
Plant carbohydrates like mannitol & trehalose passed to fungi
20. Benefits to trees
Numerous studies have shown that tree growth is better when
mycorrhizae are present
Fungi increase supply of inorganic nutrients to tree
Plant hormones produced by fungus changes the physiological state
of roots – physiologically active root area for nutrient and water
absorption is increased
Increases tolerance of plant to drought, high temperatures, pH
extremes, heavy metals
Increases resistance to infection by root pathogens – provides a
physical barrier
22. Ectomycorrhizal fungi
Can also grow saprotrophically
Many have been cultured
Most do not have the capability to degrade complex plant
polymers (e.g. cellulose and lignin)
Depend on soluble carbohydrates
Many have organic growth factor requirements – vitamins, amino
acids
Not decomposers but depend on plant
23. Benefits to fungus
Provided with source of carbon (C) and energy (Plants
provided with CO2 demonstrated that C appears in
fungus)
Sucrose from plant converted into trehalose & mannitol
by fungus
Estimates that up to 10% (or more) of photosynthate
produced by trees is passed to mycorrhizae and other
rhizosphere organisms
24. Endo/arbuscule mycorrhiza (AM)
Most common
Fungi : Glomeromycetes
Host : wild crop plants (90 %) & tropical trees
Grows in between the cells of the plant.
Mycorrhiza increase the surface area of the root.
Absorb nutrients from soil especially phosphorus and
micronutrients through hyphae and mobilize into the host cell.
25. Features
Mycorrhiza possess vesicles and arbuscules.
Not as well characterized as ectomycorrhizae
Root is not altered in morphology – difficult to determine
when roots are infected – must clear and stain followed by
microscopic examination
Fungi are obligate biotrophs – cannot be grown in axenic
culture – so difficult to conduct experiments
26. Spores
•Form large spores that superficially resemble zygospores, but not formed from fusion of
gametangia
•Spore diameters range from 50 to 400 μm
27. Arbuscules
Fungal hyphae- penetrate cortical cells- grow
intracellularly- form coils, swellings/ minute branches-
arbuscule (minute branches).
Surrounded by plant cell membrane
Typically disintegrate after 2 weeks in plant cell and
release nutrients
Thought to be site of nutrient exchange
29. Process of colonization by AM fungi
Breakdown of plant C storage
Germination of fungal pores
External molecular signal exchange between plant & fungi
Appresorium development
Host cell release branching factors
Fungal hyphal branching
Hyphae colonize root cells forming arbuscule
33. Functions of fungi
Resistance to disease, drought, nematodes & other pests
P transfer to plant.
N transfer:
Intracellular
fungal C pool
Extracellular
fungal C pool
Hexose
Plant root cell
Amino acids
NH4 Ornithine
Urea Arginine
Intracellular mycelium
NH4
Amino
acids
Protein
NO3 NO3
NH4 NH4
Glutathione
Arginine
Extracellular mycelium
35. Vesicular Arbuscular mycorrhizae (VAM)
Most common – 90% vascular plants
Host : cultivated & wild plants and found in bryophyte,
pterodophytes, gymnosperms & angiosperms.
Fungi: family Endogonacea of Zygomycotina.
Hyphae: aseptate, intra- & inter- celullar in cortex
Its development played a crucial role in the initial colonization of
land by plants and in the evolution of the vascular plants.
36. • VAM fungi capture nutrients like P, S, N and micronutrients from the soil.
• Form arbuscules and vesicles
• Vesicles :-
a. Spherical- oval intercalary, terminal, thickwalled structures, formed in the
intracellular spaces or occasionally in the cortex cells.
b. Radial & multinucleate
c. Have fat granules
d. Act as storage organ
e. Upon degeneration & eventual decomposition they provide nutrition to host.
38. Arbutoid mycorrhizae
Host : woody shrubs & tress - order Ericales
Roots : herorhizic
Mycosymbionts: Basidiomycetes
Fungi penetrate cortical cells & form hartig net
Sometimes show transition between ecto- & endo-
mycorrhizae – ectendomycorrhizae
39. Fungal sheath or mantle (20 - 80 mm) covers the roots
Nutrients scavenged by the mycelium and rhizomorphs
have to pass through the sheath and into the short roots.
The sheath - an important store of nutrients, to be released
to the plant when nutrient levels are sufficiently depleted.
Similar to ectomycorrhiza except that it’s hyphae
penetrate the outer cortical cells & form coils that the
latter can’t.
42. Monotropoid mycorrhizae
Host:-
a. Achlorophyllus plants of the family Monotropacea
b. Completely depend on the fungus for C & energy
c. Roots form ball throughout which fungal mycelium ramifies enclosing the
roots of neighboring green plants.
Fungi: Basidiomycetes
Root ball:-
a. survival organ during winter
b. form flowering shoots during favorable condition
Form sheat & hartig net
Structure & function change with seasonal development of host.
48. NAMATODES
Nonsegmented roundworms of the phylum Nematode
Majority are free-living in soil & fresh and salt waters
Has a flexible outer cuticle that protects them
Move via muscular system
49. Most lay eggs
Predominantly pathogenic for plants
Some are human parasites & others animal parasites
Enemy: nematophagous fungi
50. NAMATOPHAGY
Eating of nematodes by fungi
Fungi - predacious/ namatophagous/ nematode trapping
Fungi mechanically attack & kill the worms resulting in
consumption of the worm
51. NEMATOPHAGOUS FUNGI
Obligate parasites of nematodes
Majority of them are facultative saprophytes
Used for biological control of plant-parasitic nematodes
Source: surface litter & decaying organic matter
52. Taxonomy and phylogeny
Fungal taxa: Ascomycetes (and their hyphomycete
anamorphs), Basidiomycetes, Zygomycetes,
Chytridiomycetes and Oomycetes
Nematophagous habit evolved from lignolytic
&cellulolytic fungi as an adaptation to overcome
competition for nutrients in soil.
53. Classification based on ecological habitat
NEMATOPHAGOUS
FUNGI
Nematode – trapping
fungi
Endoparasitic fungi Egg parasites
54. Nematode – trapping fungi
Capture nematodes
Have structural adaptations
Predatory/ endoparasites
They traps host & kill it.
55. Mechanisms of trapping
a. Adhesive hyphae
b. Adhesive branches
c. Adhesive nets
d. Adhesive knobs
e. Non- constricting ring
f. Constricting rings
56. Adhesive hyphae
Nematode contact with fungal hyphae
Worm remains in contact (secreted/ coated adhesive)
Secretion of yellow, thick chemical
Hyphal outgrowth development
Complete trapping of worm
Inactivation of worm
Worm cell penetration by hyphae
Elongation & nutrient absorption by unbranched hyphae
Death of worm
59. Adhesive branches
Small & simple organ of capture
Few cells in height
Arise from main prostate hyphae as short laterals & grow
as erect branches on/ below the substrate
Is coated with a thin film of adhesive materila
Example of fungi: Dactylella cinopaga
61. Adhesive nets
Formed by adhesive fungal hyphae
Single loop like – complex multibranched network
Example: Anthrobortrys musiformis
Action similar to that of adhesive hyphae except that they
never secrete adhesive material but coated.
62.
63. Adhesive knobs
Distant adhesive globose- sub- globose cell
Produced at the apex of a slender non- adhesive stalk
with 1- 3 cells
Action:-
Production of a thin adhesive film over the knob surface
Nematode trapping by knob
Attack by several more knobs
Knob penetration
Nematode death
65. Non- constricting ring
Formed by erect, lateral branches that arise from the prostrate creeping
septate hyphae
Action:-
a. Slender branch widens
b. Branch curls to form circular structure
c. Cell wall of stalk & tip of branch fuses at the point of contact
d. 3- celled ring with a stalk
e. Nematode entry into ring
f. Worm moves forward
g. Marked constriction of hyphal cuticle
h. Nematode struggling
i. Breakup of weak points of the ring
j. Worm movement carrying ring
k. gradual penetration of nematode by the ring
l. Nematode death
67. Constricting rings
Produced similar to that of the non- consticting one
Here the supporting stalk is shorter & stouter
3- celled ring
Example: Arthrobotrys anchonia
68. Action of ring
Nematode entry into ring
Ring swallow the nematode in a single hold
Induction of ring swelling out of friction
Deep constriction of worm’s body
Struggling for few minutes
Inactivation of prey
Hyphal penetration & exploitation
Prey death
69.
70.
71.
72. Endoparasitic fungi
Produce mycelium externall to nematode body
Bring modifications in conidia to kill their prey
Cephalosporium, Meria, Catenaria, etc.
C. anguillulae zoospores track down worms by swarming,
eventually encyst near nematode’s body orifice, penetrate
& colonize the prey.
