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

Monday, August 2, 2010

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

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

Monday, July 19, 2010

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

B. Metabolism of germination stimulants

C. Trichoderma as an antagonist of nematodes

Tuesday, June 8, 2010

Apple Tree: Low Productivity in Apple: Strategies to Overcome

This post is in continuation to my previous post on Short term strategies to overcome the low productivity problems in apple
Following are the strategies that are needed to be adopted and farmers at field level are to be made aware of these strategies: There are two types of strategies viz. Short term strategies and Long term strategies Here I shall be discussing the Long Term Strategies to Overcome the Low Productivity in Apple
  • Promoting high density plantation by using suitable rootstock and Spur type varieties for reducing the gestation period and increasing production per unit area
  • Phasing out old plantations, which have completed their economic life, and replanting with new apple varieties on suitable rootstock.
  • Introducing improved varieties of apple, which are regular bearers, heavy croppers, precocious, resistant to biotic and abiotic stresses and also useful for processing purpose
  • Identification fruit trees of outstanding merit in existing apple plantations for use as mother trees when establishing future orchards
  • Developing of infrastructure and facilities for multiplication of certified virus tested planting material of apple rootstock and scion varieties for use in future apple orchards
  • Expansion of area under improved varieties of apple
In coming posts I shall be discussing about plant health management.

Thursday, May 6, 2010

Low Productivity in Apple: Strategies to Overcome

I am continuing after a long gap for some technical reasons especially pertaining to internet problems I am facing in the Tribal Area. This post is in continuation with the previous posts on the Low productivity in Apple. Now I shall be discussing on the strategies for improving the production, productivity and quality of apples .
Following are the strategies that are needed to be adopted and farmers at field level are to be made aware of these strategies:
There are two types of strategies viz. Short term strategies and Long term strategies
Today I shall be discussing only the Short Term Strategies
  • Improving orchard management techniques in particular the training and pruning of apple plants. This is the most important and crucial practice and extension workers as well as farmers must be trained in this technique
  • Plantation of an adequate number of pollinizing varieties and the introduction of honey bees for effective pollination
  • Water, being vital to apple fruit production, farmers should develop their own water harvesting facilities and install the drip irrigation system in the orchards on a large scale
  • Adoption of modern plant tissue analysis technique for the diagnosis of nutrition problems in apple orchards, and the formulation of fertilizer schedules for each orchard based on this technique
  • Promotion of scientific soil and water conservation techniques in apple orchards
  • Undertaking timely measures for the control of pests and diseases of economic importance by adoption of integrated spray schedules. For this purpose IPM strategies are also required.
  • Provision of antihail nets for protecting the crop against hail damage
  • Rejuvenation of old apple orchards through pruning and judicious fertilizer application
  • Promotion of the concept of fruit thinning in Delicious group of cultivars which has tendency of alternative bearing
In the next post I shall be discussing the the Long Term Strategies to Overcome Productivity Problems