Biomedical Engineering Reference
In-Depth Information
(2) Hyperparasitism
Hyperparasitism refers to a series of complex processes, including identifica-
tion, contact, twining, penetration, and parasitism. After the identification of
Trichoderma
spp. to host pathogen, its hyphae can directly invade or wrap around
the host hyphae cell, penetrate the mycelia of the pathogen, and absorb nutrients
by secreting extracellular enzymes to dissolve the cell walls [
51
], which causes
the enlargement, deformation, or shrinkage of the pathogen cell, the contraction
of protoplasm, and the rupture of the cell wall.
(3) Antibiosis
Trichoderma
spp. can produce antagonistic chemicals against plant pathogens in
their metabolic processes, including antibiotics and enzymes, such as trichodermin,
neomycin, green trichodermin, and antimicrobial peptides.
(4) Collaborative antagonism
The collaborative antagonism of
Trichoderma
spp. may be the result of integration
of simultaneous or sequential action of two or three mechanisms. Baker's research
showed that the functions of
Trichoderma
to
Pythium
included the two mechanisms
of antibiotic production and hyperparasitism.
Trichoderma
spp. not only can
produce antibiotics but also can secret a variety of extracellular enzymes to degrade
the cell wall and inhibit mycelial growth and spore germination of soil-borne plant
pathogens. Corella et al. proposed the synergistic effect model of mycin and the
cell-wall-degrading enzymes and believed that the function of cell-wall-degrading
enzymes was to make toxins quickly transmit and interact with the specific sites of
plasma. Moreover, there is a synergistic role among the different cell-wall-degrading
enzymes [
51
].
(5) Induced resistance
Previous studies of the mechanism of biocontrol focused on the interaction between
microorganisms and ignored the role of the host plants. Researches recently found
that biocontrol agents can induce each part of the organization of the host plant
to form resistance to pathogens. As reported, when the hyphae of biocontrol
microorganisms penetrate the epidermis cortex of cucumber roots, the peroxidase
content increased in the plant, and the chitinase activity of the plant increased at the
same time [
48
].
5.3.1.4
Fermentation of
Trichoderma
spp.
The first problem to solve is obtaining a large amount of
Trichoderma
cells if
Trichoderma
is widely used to control plant diseases. Because of the special
nutritional and environmental conditions needed for
Trichoderma
growth, it is
not easy to obtain a great quantity of biomass. Because the biocontrol effect of
Trichoderma
is widely accepted, there are numerous reports of
Trichoderma
culture
matrix and fermentation production, including liquid culture, solid-state culture, and
solid-liquid biphasic fermentation.
