Introduction
Biological control, the use of specific microorgan-
isms that interfere with plant pathogens and pests, is
a nature-friendly, ecological approach to overcome
the problems caused by standard chemical methods
of plant protection. Commercial preparations for plant
disease biocontrol are all based on the practical ap-
plication of a few species of rhizosphere-competent
bacteria and more than 10 species of fungi (Chernin
& Chet 2001). The general mechanism of biological
control can be divided into direct and indirect effects
of the biocontrol agent (BCA) on the plant patho-
gen. Direct effects include competition for nutrients
or space, production of antibiotic and lytic enzymes,
inactivation of the pathogen’s enzymes and parasit-
ism. Indirect effects include all those aspects that
produce morphological and biochemical changes in
the host plant, such as tolerance to stress through en-
hanced root and plant development, solubilization or
sequestration of inorganic nutrients, and induced res-
istance. Plants are capable of producing an immune
response after a primary pathogen infection known
as systemic acquired resistance (SAR) (van Loon et
al. 1998). The activation of SAR correlates with the
expression of pathogenesis-related (PR) genes, includ-
ing acidic and basic β-1,3-glucanases and chitinases
which supposedly act against the pathogen cell walls.
Non-pathogenic rhizobacteria and fungi can induce a
systemic resistance in plants (ISR) that is phenotyp-
ically similar to SAR (van Loon et al. 1998; Park
& Kloepper 2000; Yedidia et al. 2000). No single
biocontrol strain is known to possess all of these mech-
anisms and their genetic and biochemical bases are
still poorly understood. However, from the currently
available data, it appears that most of these processes
are caused by multi-gene complexes (Harman 2000).
In the present review, we detail the lytic apparatus
of the well-known BCATrichoderma,concentrating
on the role of its lytic enzymes in the biocontrol of
soilborne fungal diseases.