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

Chapter 6
Many preparations have been developed to ensure a good shelf life of the product based on
Trichoderma. Some of that formulation are stable in terms of pH, that remains constant and low
(5.5) during the entire growth period, thus preventing bacterial contamination. Moreover the shelf
life of the fungus at 25 °C is 1 year and from 1 to 2 years, the number of colonies-forming-units
(CFUs) decreases by one order of magnitude. Many of that formulation have been proven
successful in several experiments in the greenhouse and field. The rapid mass production of
promising antagonists in the form of spores, mycelia or mixtures of both, has been achieved by
liquid-fermentation technology: mass production of biomasses of T. hamatum, T. harzianum, and T.
viride was reached by utilizing commercially available, inexpensive ingredients such as molasses,
brewer's yeast, cotton seed flour, or corn-steeped liquor.. Other techniques have been employed to
improve the delivery of the biocontrol agents. A lignite-stillage (a by-product of sorghum
fermentation) carrier system was tested for applying a T. harzianum preparation to the soil.
Encapsulation of the biocontrol agent in an alginate-clay matrix, using Pyrax as the clay material,
improved yield and propagule viability over time.
Pelletized formulations of wheat bran or kaolin clay in an alginate gel containing conidia,
chlamydospores or fermentex biomass of several Trichoderma isolates revealed increased viability
of stored pellets, and the number of CFUs formed after adding these pellets to the soil was
comparable to that formed from freshly prepared pellets. These growth media and delivery systems
for formulations of biocontrol fungi show promise because they are able to introduce high levels
(10 6- 10 10 CFU/g) of fungi into soils not steamed, fumigated, or treated with other biocides.
To enhance biocontrol efficacy, appropriate introduction of the antagonist into the
microenvironment appears to be crucial: formulations have been applied to seedlings prior to
planting or to seeds in furrows. Economic considerations have forced biotechnologists to improve
the application techniques: seed-coating, a technique involving minimal amounts of inoculum was
developed.
Increased biocontrol activity may be achieved by combining two types (or more, if possible) of
biocontrol agents, for example combining Trichoderma with a bacterium, or another beneficial
fungus. The combined activity of the antifungal compounds produced by both microorganisms
could expand the spectrum of pathogens controlled. In fact, in field trials combining T. koningii
with certain fluorescent pseudomonads, greater suppression of take-all disease and increased wheat
yield were achieved relative to plants treated with T. koningii alone (Duffy et al. 1996).Delivery
systems must ensure that biocontrol agents will grow well and achieve their purpose. It is generally
recognized that delivery and application processes must be developed on a crop by crop and
application by application basis. No general solutions exist, and so biocontrol systems must be
developed for each crop. It is very important to use the organism properly and to have appropriate
expectations. Any biocontrol organism will be unable to protect seeds as well as chemical
fungicides. However, it colonizes roots, increases root mass and health, and consequently frequently
provides yield increases, which chemical fungicides applied at reasonable rates cannot do. An
effective method of use is to use the biocontrol fungus in conjunction with chemical fungicides. The
chemicals provide good short-term seed protection, and the biocontrol fungus provides long-term
root protection. As a consequence, yields frequently are increased over use of the chemical alone.
Some experiences evidence that Trichoderma spp. is also highly effective when applied to
blossoms or fruits for control of B. cinerea. Even low levels of the organism applied to strawberry
blossoms by bee delivery or by sprays of liquid formulations are effective. For maximum control of
the Botrytis bunch rot of grape, this initial application needs to be augmented by sprays as fruits
mature, and addition of iprodione as a tank mix to this late application appears to have synergistic
activity over either the biocontrol agent or the chemical fungicide alone.
Novel applications of Trichoderma spp. Trichoderma spp. produce a variety of lytic enzymes that
have a high diversity of structural and kinetic properties, thus increasing the probability of this
fungus to counteract the inhibitory mechanisms used by neighbouring microorganisms. Further,
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