Siderophore Production by Trichoderma

This post is in continuation to Competition and Rhizosphere Competence of Trichoderma: A Magical plant health manager.

Siderophores (Gr. “iron-bearers”) are defined as ‘low molecular weight, virtually ferric specific legends, the biosynthesis of which is carefully regulated by iron and the function of which is to supply iron to the cell’. Iron is generally present in the microbial environment as the ferric ion (Fe (III)), which is virtually insoluble in the presence of O2 and therefore, is not available for microbial growth. Siderophore chelate Fe (III) and microbial membrane receptor proteins specifically recognize and take-up the siderophore-Fe-complex. This results in making iron unavailable to rhizosphere microorganisms, including plant pathogens, which produce less or different siderophores with lower binding coefficients. The result is less pathogen infection and biological control. Siderophores also help in improving antagonistic activities, rhizosphere competence and plant growth.
Trichoderma virens is reported to produce three types of hydroxymate siderophores: a monohydroxamate (cis- and trans-fusarinines), a dipeptide of trans-fusarinine (dimerum acid), and a trimer disdepsipeptide (copragen).

In coming post I shall be discussing more about

-->TRICHODERMA AS A BIOFERTILIZERS & PLANT GROWTH PROMOTER

Competition and Rhizosphere Competence

This post is in continuation with my previous posts on Mechanisms of Anti-fungal Actions of Trichoderma A Magical Plant Health Manager. Today I shall be discussing about the most accepted mechanism of antifungal action Biological Control Agents (BCAs) i.e. Competition and Rhizosphere Competence

Competition is considered as 'classical' mechanism of biological control. It involves competition between antagonist and plant pathogen for space and nutrients. The idea of the involvement of this mechanism in biocontrol by Trichoderma has gained popularity in recent years.

The omnipresence of Trichoderma in agricultural and natural soils throughout the world proves that it must be an excellent competitor. For example, B. cineria conidia require external nutrients for germination and infection when conidia of Trichoderma sp were applied to leaves, germination of conidia of the pathogen was slowed, an effect attributed in part to competition. The competitive ability of Trichoderma and therefore its biocontrol potential is affected by soil properties.
In coming posts I shall be talking about Siderophore Production by the Trichoderma species. These help in plant growth promotion........

Antibiosis: Mechanisms of Antifungal Action

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This post is a continuing series of the Trichoderma a Magical Plant Health Manager:

and part of the Mechanism of Anti-fungal Action of Trichoderma

This is the second major mechanism implicated in the biocontrol of pathogens by Trichoderma. Trichoderma species are reported to produce a number of antibiotics. These include gliotoxin and glioviridin from T. virens, viridin, alkyl pyrones, isonitriles, polyketides, peptaibols, diketopiperazines, sesquiterpenes and some steroids from other Trichoderma species.

My next post will be on the most accepted mechanism of anti-fungal action of the BCAs i.e. Competition .

Mechanisms of Antifungal Action of Trichoderma:Enzymes

Its quite a long time I have posted anything on this blog. There were certain technical reasons for not posting the anything. Now the problems seams to be resolved therefore I shall be continuing on Trichoderma a Magical Plant Health Manager.


Most of the pathogenic fungi contain chitin and Beta-glucans in their cell walls. Dissolution or damage of these structural polymers has adverse effects on the growth of these fungi. Recent research work has implicated a major role of enzymes in biological control by Trichoderma species and the secretion of enzymes is reported to be an integral step of the mycoparasitic process of Trichoderma. Trichoderma species secrete a number of hydrolytic enzymes, which includes chitinases, proteases, cellulases, glucanases and xylanases. Chitinases and beta-1,3 glucanases secreted by T. harzianum plays an important role in degrading hyphae of S. rolfsii. Various enzymes that are present in the different Trichderma species includes protease, beta-1,4-glucanases, exo alpha-1,3- glucanase (AGN 13.1).

Dear Sharad as you have suggested that I shall write on Apple Diseases one by one, surely I shall be writing after finishing off this topic. Hope you will bear with me....

Mechanism of antifungal action

I was writing on Trichoderma as Biological Control Agent, during last fortnight was going through some literature on biological control agents which says that

--> agriculture in developed countries undergoes continuous change often based on new introductions, some based on customer preferences and some based on ethical considerations. This is particularly true of crop protection. The global consensus to reduce inputs of chemical pesticide which are perceived as being hazardous by some consumers has provided opportunities for the development of novel, benign, sustainable crop protection strategies. A great many chemical pesticides have been or are being phased out (e.g. organochlorine insecticides, methyl bromide) either because of potential human health risks, environmental pollution, effects on non-target organisms or the development of pest resistance. Today’s new chemical pesticides are significantly more benign than yesterday’s products, but will these products ever receive registrations on small area crops or in subsistence agriculture? Are there any alternatives to chemical crop protection? There is no doubt that there is a need to develop alternative control systems in the new future and these must be implemented to replace or complement conventional pesticide usage. Therefore this becomes more important to understand about various sustainable methods of crop production/ protection. Biological control agents are one among those. Trichoderma a magical plant health manager is one which has been studied vastly. How it works is very important.
Today I shall be writing about this....

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Against fungal pathogens, Trichoderma species rely on three major mechanisms viz. mycoparasitism/ hyperparasitism, antibiosis and competition.

i. Mycoparasitism/ Hyperparasitism

One of the most salient characters of the genus Trichoderma is its ability to

parasitize other fungi. Weindling in 1932 for the first time described the biocontrol of R. sol

ani (causing citrus seedling disease) by Trichoderma lignorum to mycoparasitism. Mycoparasitism is a complex process involving tropic growth of the biocontrol agent towards the target

organism, coiling and finally dissolution of the target organism’s cell wall/cell membrane by the activity of enzymes. (Rather than coiling, hyphae of Trichoderma may grow attached

with hyphae of R. solani, form haustoria, which may penetrate host fungal cell to draw nutrients.

In coming posts I shall be further discussing about the

i) Mycoparasitism/ Hyperparasitism ii) Enzymes iii) Antibiosis
iv) Competition and rhizosphere competence v) Siderophore production
vi) Signal Transduction

Trichoderma as Biological Control Agent

Last time I started writing on Trichoderma a Magical Plant Health Manager. This post is in continuation to the above Topic. Today we shall be discussing here the Trichoderma as Biological Control Agent (BCA).

Weindling in 1932, for the first time implicated the role of Trichoderma lignorum in the biological control of citrus seedling disease caused by Rhizoctonia solani. Since this pioneering work, several reports on successful biocontrol by Trichoderma spp. have accumulated. T. harzianum, T. viride and T. virens are the most widely used/cited for biological control. They are reported effective in controlling root rots /wilt complexes and foliar diseases in several crops (Singh et al., 2004, 2005, 2006; Zaidi and Singh, 2004) and are reported to inhibit a number of soil borne fungi like Rhizoctonia, Pythium, Sclerotinia, Sclerotium, Fusarium spp., Macrophomina etc. and recently root knot nematode, Meloidogyne spp.

Biocontrol activity of Trichoderma is due to combination of its ability to serve as antagonist, plant growth promoter, plant defense inducer, rhizosphere colonizer and neutralizer of pathogen’s activity favouring infection.

Trichoderma as a fungal antagonist
As an antagonist, Trichoderma may directly kill the pathogen by mycoparasitism and/or antibiosis. Also, it may adversely affect the growth of the pathogen either by antibiosis or by competing for the nutrient,oxygen or space. Indirectly, it may promoting plant growth which manifests itself as root and shoot growth. resistance to biotic and abiotic stresses and changes in the nutritional status of the plant.

In coming posts I shall be mainly concentrating on the Mechanisms of anti fungal action with following subheadings

i) Mycoparasitism/ Hyperparasitism
ii) Enzymes
iii) Antibiosis
iv) Competition and rhizosphere competence
v) Siderophore production
vi) Signal Transduction

Trichoderma a Magical Plant Health Manager

I am continuing after a gap on health management. I have discussed with you about plant health management principles among these Biological control is very important. Trichoderma is one of the important biological control agent that is better known as plant health manager. In my coming posts I would like to discuss about the mechanisms of the plant health management that are dealt with by Trichoderma.

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Trichoderma species are free-living fungi that are common in soil and root ecosystems throughout the world. They are highly interactive in root, soil and foliar environment. They are presently in nearly all types of soils and other natural habitats especially those containing high organic matter. This fungus is a secondary colonizer and is frequently isolated from well decomposed organic matter. Trichoderma species have also been isolated from root surfaces of various plants, from decaying barks and from sclerotia and propagules of other fungi. In general the members of Trichoderma exhibit a preference for wet soils. While species like T. viride and T. polysporum are generally found in areas with low temperature, T. harzianum most commonly occurs in warm climatic regions. T. hamatum and T. koningii have been reported to occur in diverse climatic conditions. The presence of carbon dioxide has been reported to favour growth of Trichoderma. Trichoderma species have the ability to utilize a wide range of compounds as sole carbon and nitrogen sources and can utilize monosaccharides, disaccharides, polysaccharides etc. for carbon with ammonia being the most preferred source of nitrogen. The members of Trichoderma are generally considered to be aggressive competitors although this trait has also been found to be species dependent.

Trichoderma spp. are highly efficient producer of many extra cellular enzymes like cellulases, chitinases, glucanases, proteases etc. They are being exploited in variety of ways like source of cellulases (used in foods and textiles and also in poultry feed) and chitinases (generating disease resistant transgenic), in plant disease control (through their anti-fungal and anti-nematode activity and in plant defense induction), improvement of plant growth, straw/compost decomposition and suppression of some of the weeds.

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All these properties can be described in my coming posts under different subheadings

A. Trichoderma as a fungal antagonist

B. Metabolism of germination stimulants

C. Trichoderma as an antagonist of nematodes

D. TRICHODERMA AS A BIOFERTILIZERS & PLANT GROWTH PROMOTER

E. TRICHODERMA AS A SYMBIONT AND DEFENSE INDUCER

F. TRICHODERMA AS A COMPOST COLONIZER