Agriculture Reference
In-Depth Information
A variety of other formulations have been examined as means to improve
application and efficacy of fungi used as weed biocontrol agents (Boyette
et al
.,
1996). For liquid formulations, which are used primarily to incite leaf and
stem diseases, the focus has been on developing better surfactants, diluents,
emulsions, and gels.
Colletotrichum gloeosporioides
f.sp.
malvae
has, for example,
been formulated in a silica gel carrier to improve dispersion of the pathogen
in water and enhance spray coverage of the target weed.For granular formula-
tions,which appear best suited to deliver pathogens that attack at or below the
soil surface, the focus has been on producing granules that buffer environ-
mental extremes, serve as alternate food sources for pathogens (thus increas-
ing their persistence), and minimize the likelihood of being washed away
from the target area. Examples include cornmeal and sand mixed with
Fusarium solani
f.sp.
cucurbitae
for control of
Cucurbita texana;
vermiculite mixed
with
Alternaria macrospora
for control of
Anoda cristata;
sodium alginate and
kaolin mixed with
Fusarium laterium
for control of
Abutilon theophrasti;
and
wheat gluten mixed with
Fusarium oxysporum
for control of
Sesbania exaltata
(Boyette
et al
., 1996).
In addition to the development of better formulation technologies for
mycoherbicides,efforts have also been directed toward improving production
and culture technologies. In general, three methods exist for producing
fungal pathogens in large quantities. Certain fungi, such as
Puccinia
spp.,
require the use of living host plants. Others, such as
Alternaria
spp., are best
adapted to solid substrate fermentations. Both of those methods are consid-
ered expensive and poorly suited to industrial-scale production. A large
number of other fungi can be produced, however, by liquid culture fermenta-
tion,which is relatively inexpensive and already widely used for pharmaceuti-
cal and food products.
The possibility of improving liquid culture media for the production of
mycoherbicides has been emphasized by Jackson
et al
. (1996), who investi-
gated the effects of varying carbon concentrations in media used to produce
microsclerotia of
Colletotrichum truncatum.
Microsclerotia of this fungus are
considered to be more desirable than conidia because of their greater stability
as dry preparations and their greater efficacy in controlling
Sesbania exaltata
when used as soil amendments. Jackson
et al
. (1996) found that media rich in
carbon (
25 g L
1
) promoted production of microsclerotia, whereas media
containing less carbon (
16 g L
1
) favored production of conidia. They con-
cluded that a better understanding of how nutritional conditions in liquid
culture media affect propagule formation, yield, efficacy, and stability will
enhance the use of fungi and other microorganisms as biocontrol agents.
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