Thursday, August 19, 2010

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....

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