Biomedical Engineering Reference
In-Depth Information
against
B. cinerea
on bean leaves. When the same gene was deleted or
over-expressed in
T. virens
, the biocontrol against
R. solani
in cotton were
signifi cantly decreased and enhanced (Baek et al. 1999). Disruption of
nag-1
, encoding a 73-kDa
N
-acetyl-β-D-glucosaminidase resulted in 30%
reduced ability of
T. atroviride
to protect bean seedlings against infection
by
R. solani
(Brunner et al. 2003). Overexpression of an endochitinase gene
(
ThEn-42
) in
Trichoderma
atroviride
increased production of antifungal
enzymes and enhanced antagonist action against pathogenic fungi
(Deng et al. 2007). Overexpression of the proteinase-encoding gene
prb1
in
T. harzianum
improved the biocontrol activity against
Rhizoctonia
solani
(Flores et al. 1997). Deletion or the overexpression of
tvsp1
, a
serine protease encoding gene in
T
.
virens
did not affect the growth rate,
conidiation, extracellular protein accumulation antibiotic profi les or
their ability to induce phytoalexins in cotton seedlings. However, Tvsp1
overexpression signifi cantly increased the ability of some strains to protect
cotton seedlings against
Rhizoctonia solani
(Pozo et al. 2004). Recently, using
similar genetic approach, Djonovic et al. (2006b) showed
tvbgn3
, a gene
encoding β-1,6-glucanase is involved in mycoparasitism and biocontrol
of
P. ultimum
by
T. virens.
Co-overexpression of two beta glunasase genes
tvbgn2
and
tvbgn3
resulted in improved biocontrol potential of
T. virens
against
P. ultimum
,
Rhizopus oryzae
and
Rhizoctonia solani
(Djonovic et al.
2006b). The cellulase formation of
T. reesei
was found to be dispensable
for the biocontrol of
P. ultimum
on zucchini plants (Seidl et al. 2006b). In
contrast to the hyphal parasitism, not much work has been done on the
genetics of sclerotia degradation by
Trichoderma
spp. However, recently
the role of a
T. virens
laccase gene
lcc1
has been studied by gene deletion
and interestingly, it was found that the deletion strain had reduced ability
to degrade
Botrytis cinerea
sclerotia while these mutants had enhanced
ability to degrade
Sclerotinia sclerotiorum
sclerotia (Catalano et al. 2011).
Secondary Metabolites
Trichoderma
spp. produce more than 100 different secondary metabolites,
some of them having antimicrobial properties (Reino et al. 2008). However,
there appear only a few genetic studies on the role of these metabolites
in biocontrol of plant pathogens. Earlier, attempts were made to obtain
mutants through classical mutagenesis that are defi cient in the production
of certain antibiotics and the role in pathogen suppression studied.
Most of such work was done with
T. virens
, which produces four major
metabolites—gliotoxin, gliovirin, viridin and viridiol (Howell et al. 1993).
Gliotoxin, one of the secondary metabolites of
H. virens
and the human
facultative pathogen
Aspergillus fumigatus
, has received much attention for
its role in biocontrol (Howell 2006). The “Q” strains of
T. virens
produce