Classical and augmentative biological control against ... - IOBC-WPRS

Ruocco et al.
Trichoderma hydrolytic enzymes have been demonstrated to be synergistic, showing an augmented
antifungal activity when combined with themselves, other microbial enzymes, PR proteins of plants
and some xenobiotic compounds (Fogliano et al. 2002; Lorito et al. 1994a, 1994b, 1994c, 1996,
1998; Schirmbock et al. 1994; Woo et al. 2002). In fact, the inhibitory effect of chemical fungicides
for the control of the foliar pathogen B. cinerea was substantially improved by the addition of
minute quantities (10-20 ppm) of Trichoderma CWDEs to the treatment mixture (Lorito et al.,
1994b).
Extensive testing of T. harzianum strain T22 conducted for the registration of this biocontrol
agent in the USA by the Environmental Protection Agency (EPA) has found that the CWDEs do not
have a toxic effect on humans and animals (ED50 and LD50), and that they do not leave residues,
but degrade innocuously in the environment. Therefore, these Trichoderma hydrolytic enzymes
present a novel product for plant disease control based on natural mycoparasitic compounds used by
the antagonistic fungi. Single or mixed combinations of CWDEs with elevated antifungal effects,
obtained from fermentation in inducing conditions, over-expression of the encoding genes in strains
of Trichoderma, or heterologous expression of the encoding genes in other microbes are possible
alternatives for pathogen control. These natural substances originating from the BCA are an
improvement over the use of the living microorganism in the production of commercial
formulations because they are easily characterized, resist desiccation, are stable at temperatures up
to 60° C, and are active over a wide range of pH and temperatures in the agricultural environment.
The important factors to consider in a commercial bio-formulation are product stability, the capacity
to produce consistent results by preserving the characteristics producing the biological effects; the
storability of the material, the ability to be conserved in unspecialized conditions similar to those of
chemical pesticides; and a reasonable shelf-life or time that the product can be stored and used
without compromising the efficacy (Agosin and Aguilera, 1998; Agosin et al., 1997; Powell and
Jutsum, 1993). When a formulation contains the living microorganism component, the treatment
must consist of stabilizing the viability of the BCA. For liquid formulations this can be achieved by
maintaining the product in refrigeration (