Mycoparasitism

A mycoparasite is an organism with the ability to be a parasite to fungi. A variety of fungicolous fungi have been found in nature, either as parasites, commensals or saprobes. Biotrophic mycoparasites get nutrients from living host cells. Necrotrophic mycoparasites rely on decayed matter (saprophytic growth). 
Types of mycoparasitism.
Biotrophic mycoparasites and nectrophic mycoparasites are two main groups of mycoparasite. 
Biotrophic and necrotrophic mycoparasites.
Biotrophic mycoparasites get nutrients from living host cells and their growth of these parasites is greatly influenced by the metabolism of the host. Biotrophic mycoparasites tend to have a high host specificity, and often form specialized infection structures or a host parasite transition. Necrotrophic mycoparasites could only rely on saprophytic growth. On the other hand, the antagonistic action is strongly aggressive in necrotrophic relationships which is dominated by necrotrophic mycoparasites. Necrotrophic parasites tend to have a low host specificity, and are relatively unspecialized in their mechanism of parasitism.
Balanced and destructive mycoparasites.
Balanced mycoparsites have little or no destructive effect on the host, whereas destructive mycoparasites have the opposite effect. Biotrophic mycoparasites are generally considered as balanced mycoparasites; Necrotrophic mycoparasites usually have low host specificity and could use toxic and related enzyme to kill host, therefore necrotrophic mycoparasites are usually considered as destructive mycoparasites. However, in some combinations, the parasite may live during its early development as a biotrophic parasite, then kill their host and change into destructive mycoparasites in their late stage of parasitization.
Myco-heterotrophy.
"Monotropa uniflora" (or other angiosperm species), which are parasitic on fungus and do not photosynthesize, are sometimes classified as mycoparasites, however they should be referred to as myco-heterotrophs.
Mechanism.
There are normally four continuous steps of mycoparasitism: target location; recognition; contact and penetration; nutrient acquisition.
Target location.
Many research indicate that the growth direction of mycelium, spore germination, and bud tube elongation of mycoparasites have tropic reaction or tropism before attaching the host fungi. This tropic reaction is resulted from chemical stimulants secreted from mycohost and the direction of concentration gradient determines the growth direction of the parasite. As the mycoparasitic interaction is host-specific and not merely a contact response, it is likely that signals from the host fungus are recognized by mycoparasites such as "Trichoderma" and provoke transcription of mycoparasitism-related genes. 
Recognition.
When mycoparasites get attachment of mycohost, they will recognize each other. It is indicated that the recognition between mycoparasites and their host fungi is related to the agglutinin on the cell surface of the mycohost. The carbohydrate residues on the cell wall of mycoparasites could specifically bind to the lectins on the surface of the host fungi to achieve mutual recognition. 
Contact and penetration.
Once mycoparasites and mycohost recognize each other, both of them would have some changes in external form and internal structure to some extents. The manifestations of the mycoparasitic fungi are usually as follows: (1) the hypha grows rapidly on the host fungi and coils around the hypha of the host fungi; (2) the hypha penetrates and elongates the hypha of the host fungi (3) the infection filament is produced and penetrates the cells of host fungi to build parasitic relationship. In terms of necrotrophic/destructive mycoparasites, on the other hand, the hyphae of host fungi, due to the role of mycoparasites, will stop the growth, deform, shrivel and even dissolve.
Application.
Recently, it is popular to use integrated pest management (IPM) as an approach to reduce the amount of pesticides used, through preventive cultural practices, the use of disease resistant plant cultivars, and the use of mechanical and biological control of pathogen populations. Biocontrol of plant pathogens by microbial antagonists is one promising component in future disease control strategies that is compatible with both organic agriculture and IPM. As some mycoparasitic fungi have the ability to parasite and kill other fungi, these fungi could be used to antagonize plant pathogenic fungi directly as biocontrol agent. Mycoparasitism of plant pathogenic fungi by "Trichoderma" isolates has been well researched and is widely considered to be a major contributing factor to the biocontrol of a range of commercially important diseases. In, among others, the United States, India, Israel, New Zealand, and Sweden have applied "Trichoderma" species commercially such as "Rhizoctonia solani", "Botrytis cinerea", "Sclerotium rolfsii", "Sclerotinia sclerotiorum", "Pythium" spp., and "Fusarium" spp. as a promising alternative to chemical pesticides. Moreover, with the better understanding of mycoparasitism, more bioactive compounds including biopesticides and biofertilizers would be introduced as beneficial products.