Trichoderma harzianum
Encyclopedia
Trichoderma harzianum is a fungus
that is also used as a fungicide
. It is used for foliar application, seed treatment and soil treatment for suppression of various disease causing fungal pathogens. Commercial biotechnological products such as 3Tac have been useful for treatment of Botrytis
, Fusarium
and Penicillium sp.
. It is also used for manufacturing enzyme
s.
Most strains are highly adapted to an asexual life cycle. In the absence of meiosis, chromosome plasticity is the norm, and different strains have different numbers and sizes of chromosomes. Most cells have numerous nuclei, with some vegetative cells possessing more than 100. Various asexual genetic factors, such as parasexual recombination, mutation and other processes contribute to variation between nuclei in a single organism (thallus). Thus, the fungi are highly adaptable and evolve rapidly. There is great diversity in the genotype and phenotype of wild strains.
While wild strains are highly adaptable and may be heterokaryotic (contain nuclei of dissimilar genotype within a single organism) (and hence highly variable), strains used for biocontrol in commercial agriculture are, or should be, homokaryotic (nuclei are all genetically similar or identical). This, coupled with tight control of variation through genetic drift, allows these commercial strains to be genetically distinct and nonvariable. This is an extremely important quality control item for any company wishing to commercialize these organisms.
Trichoderma readily colonizes plant roots and some strains are rhizosphere competent i.e. able to grow on roots as they develop. Trichoderma spp. also attack, parasitize and otherwise gain nutrition from other fungi. They have evolved numerous mechanisms for both attack of other fungi and for enhancing plant and root growth. Different strains of Trichoderma control almost every pathogenic fungus for which control has been sought. However, most Trichoderma strains are more efficient for control of some pathogens than others, and may be largely ineffective against some fungi.
Trichoderma spp. continue to be a major source of contamination and crop loss for mushroom farmers.
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
that is also used as a fungicide
Fungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
. It is used for foliar application, seed treatment and soil treatment for suppression of various disease causing fungal pathogens. Commercial biotechnological products such as 3Tac have been useful for treatment of Botrytis
Botrytis cinerea
Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as botrytis bunch rot; in horticulture, it is usually called grey mould or gray mold.The fungus gives rise to two different kinds of...
, Fusarium
Fusarium
Fusarium is a large genus of filamentous fungi widely distributed in soil and in association with plants. Most species are harmless saprobes, and are relatively abundant members of the soil microbial community. Some species produce mycotoxins in cereal crops that can affect human and animal health...
and Penicillium sp.
Penicillium
Penicillium is a genus of ascomycetous fungi of major importance in the natural environment as well as food and drug production. Members of the genus produce penicillin, a molecule that is used as an antibiotic, which kills or stops the growth of certain kinds of bacteria inside the body...
. It is also used for manufacturing enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s.
Taxonomy and genetics
Most Trichoderma strains have no sexual stage but instead produce only asexual spores. However, for a few strains the sexual stage is known, but not among strains that have usually been considered for biocontrol purposes. The sexual stage, when found, is within the Ascomycetes in the genus Hypocrea. Traditional taxonomy was based upon differences in morphology, primarily of the asexual sporulation apparatus, but more molecular approaches are now being used. Consequently, the taxa recently have gone from nine to at least thirty-three species.Most strains are highly adapted to an asexual life cycle. In the absence of meiosis, chromosome plasticity is the norm, and different strains have different numbers and sizes of chromosomes. Most cells have numerous nuclei, with some vegetative cells possessing more than 100. Various asexual genetic factors, such as parasexual recombination, mutation and other processes contribute to variation between nuclei in a single organism (thallus). Thus, the fungi are highly adaptable and evolve rapidly. There is great diversity in the genotype and phenotype of wild strains.
While wild strains are highly adaptable and may be heterokaryotic (contain nuclei of dissimilar genotype within a single organism) (and hence highly variable), strains used for biocontrol in commercial agriculture are, or should be, homokaryotic (nuclei are all genetically similar or identical). This, coupled with tight control of variation through genetic drift, allows these commercial strains to be genetically distinct and nonvariable. This is an extremely important quality control item for any company wishing to commercialize these organisms.
Mycoparasitism
Trichoderma spp. are fungi that are present in nearly all soils. In soil, they frequently are the most prevalent culturable fungi. They also exist in many other diverse habitats.Trichoderma readily colonizes plant roots and some strains are rhizosphere competent i.e. able to grow on roots as they develop. Trichoderma spp. also attack, parasitize and otherwise gain nutrition from other fungi. They have evolved numerous mechanisms for both attack of other fungi and for enhancing plant and root growth. Different strains of Trichoderma control almost every pathogenic fungus for which control has been sought. However, most Trichoderma strains are more efficient for control of some pathogens than others, and may be largely ineffective against some fungi.
Trichoderma spp. continue to be a major source of contamination and crop loss for mushroom farmers.