Vesicular Arbuscular Mycorrhizal

Vesicular Arbuscular Mycorrhizal fungi and their role in plant disease
control
P.P.Jambhulkar and S. Ramesh Babu
Agriculture Research Station, Banswara
Plant roots provide an ecological niche for many microorganisms that abound in soil.
German botanist Albert Bernard Frank in 1885 introduced the Greek word mycorrhiza which
literally means “ fungus roots”. Most plant roots form mycorrizal association with certain
fungi in soil which perform function of root hair. Mycorrhizal association generally enhances
the growth and vigour of host plants. In addition mycorrhizal; plants have greater tolerance to
toxic heavy metal, root pathogens, draught, high soil temperature, soil salinity, adverse soil
pH and transplantation shock. Most common type of mycorrhizal association is vesicular
arbuscular mycorrhizal (VAM).The increased plant growth is attributed to enhanced uptake
of diffusion limited nutrients, hormone production, biological nitrogen fixation, draught
resistance and suppression of root pathogens. VAM fungi can act as biocontrol agents for
alleviating the severity of disease caused by root pathogenic fungi, bacteria and nematodes.
Mycorrhizal association increase capacity for nutrient acquisition also improves plant heath
through a more specific increase in protection.
Vesicular Arbuscular Mycorrhiza
Vesicular Arbuscular Mycorrhiza are commonly found in association with

agricultural crops, most shrubs, most tropical tree species and some temperate tree species.
VAM has been observed in 1000 genera of plants representing some 200 families. Families
not forming VAM include Pinaceae, Betulaceae, Orchidaceae, Fumariaceae,
Commelianaceae, Urticaceae and Ercaceae. Families that rarely form VAM include
Brassicaceae, Chenopodiaceae, Polygonaceae and Cyperaceae. Most of the VAM fungi have
vast host range. The fungi associated are non septate Zygomycetous fungi belonging togenera
Glomus, Gigaspora, Acaulospora foveata and A. tuberculata.
These fungi are obligate biotrophs. VAM fungi are recommended for nursery raised
plants which later transplanted in the field. Role of VAM fungi is to improve plant growth
which attributes to increased nutrients uptake, especially phosphate; due to exploration by
external hyphae of soil beyond the root hair zone. VAM also directly affects the level of plant
hormones like cytokinins and gibberellins like substances.
Uses of VAM
 Improves uptake of phosphorus and zinc.

 Improves crop growth
 Improves nitrogen fixation
 pH tolerance
 Imparts disease and pest resistance to plants
 Increase uptake of immobile nutrients
 Imparts greater draught tolerance to plants
 Conditioning of soil
Mechanism of suppression of root pathogens by VAM fungi
Mechanism of suppression may be due to morphological, physiological and biological

alterations in the host.
Morphological alterations:
VAM colonisation increase in branching, resulting in relatively larger proportion of

higher order roots in the root system. VAM association thickens cell wall through
lignifications, thus prevents penetration by pathogens like F.oxysporum and Phoma
terrestris. Histopathological study of gall caused by Meloidogyne spp. Has fewer giant cell of
syncitia, which needed for development of nematode larvae, compared to nonmycorrhizal
plants.
Physiological and biochemical alterations:
Improved nutrient status of the host plants: Increased nutrient uptake by VAM
symbiosis results in more vigorous, tolerant and resistant plants.
Competition for photosynthesis:
Both VAM fungi and root pathogens compete for carbon compounds reaching the
roots. When VAM fungi have primary access to photosynthates, the higher carbon demand
may inhibit pathogen growth. Colonisation by VAM alters host physiology and in turns the
root exudation pattern. Decreased root exudation in mycorrhizal plants because of increased
membrane phospholipid content, helps in reducing the infection by root pathogens.
Higher level of Phenols and aminoacids:
Higher concentration of orthodihydroxy phenols present in mycorrhizal plants found

inhibitory to root rot pathogen Sclerotium rolfsii. Higher level of aminoacid arginine in the
root extract of mycorrhizal plant reduces Thielaviopsis basicola chlamydospores production.
Increased phenylalanine and serine in tomato root due to inoculation with Glomus
faciculatum.

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Vesicular Arbuscular Mycorrhizal fungi and their role in plant disease

Agriculture Research Station, Banswara

Vesicular Arbuscular Mycorrhiza

Vesicular Arbuscular Mycorrhiza are commonly found in association with

 Improves uptake of phosphorus and zinc.

Mechanism of suppression of root pathogens by VAM fungi

Mechanism of suppression may be due to morphological, physiological and biological

VAM colonisation increase in branching, resulting in relatively larger proportion of

Physiological and biochemical alterations:

Competition for photosynthesis:

Higher concentration of orthodihydroxy phenols present in mycorrhizal plants found

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