RAPD-PCR in conjunction with techniques we
developed for rapid extraction of yeast DNA,
proved to be a useful tool to test whether the
yeasts retrieved from the grape surface after field
application were, in fact, the ones that had been
applied.
In field tests reduction of bunch-rots was significant
in most cases. A pre-harvest augmentation
spray did not increase the antagonistic effect.
This can be explained by the fact that the antagonists
survived well on the fruit for 2 weeks and
more. The results of the table grape experiment in
1998 in which no reduction in decay development
was achieved, may be due to the lower survival of
the antagonist in that year during which extremely
high temperatures occurred.
Many factors can affect the survival of the
bio-antagonist as they affect the development of
the rot causing organisms (Stapelton and Grant,
1992; Elad and Kirshner, 1993). Dik (1990)
showed that development of a yeast population
on wheat depends on air temperature, humidity
and broad-spectrum fungicides (Captan). Although
the biological control agents we used in
this study were indigenous to the vineyard, their
efficient use and the number of times they should
be applied before harvest will depend on factors
affecting the physical and chemical microclimate.
Those affects must be determined in order to
improve their biocontrol efficacy.
The future use of biological agents for disease
control will depend greatly on the price of the
product, which, in turn, will depend on the ease of
growing the organism (Fokkema, 1996) and on
the dilution factor needed from culture to commercial
spray. When we worked with small clusters,
instead of checking the exact concentration
of the antagonist in suspension, we used a dilution
factor of 1:10 from the concentration at the stationary
phase of each antagonist. Different organisms
reach the stationary phase at different
concentrations and strains that can be effective at
a high dilution rate will be less expensive as
control agents.
Chemical control of grape decay is difficult
because of the diverse fungi involved. The chemicals
we used gave adequate control of B. cinerea
but only the newly registered fungicide
Pyrimethanil (applied in 1998) protected the
grapes from A. niger rot, the predominant fungus
on wine grapes. The antagonists, though less efficient
against this fungus, in most cases, reduced
the percentage of diseased clusters. One of the
problems with chemical control is the hazard to
the consumers and an IPM program combining
early chemical sprays, to reduce the level of fungal
inoculum, with antagonist application close to
harvest, could be the logical solution to benefit
consumers, growers and the environment.
RAPD-PCR in conjunction with techniques we
developed for rapid extraction of yeast DNA,
proved to be a useful tool to test whether the
yeasts retrieved from the grape surface after field
application were, in fact, the ones that had been
applied.
In field tests reduction of bunch-rots was significant
in most cases. A pre-harvest augmentation
spray did not increase the antagonistic effect.
This can be explained by the fact that the antagonists
survived well on the fruit for 2 weeks and
more. The results of the table grape experiment in
1998 in which no reduction in decay development
was achieved, may be due to the lower survival of
the antagonist in that year during which extremely
high temperatures occurred.
Many factors can affect the survival of the
bio-antagonist as they affect the development of
the rot causing organisms (Stapelton and Grant,
1992; Elad and Kirshner, 1993). Dik (1990)
showed that development of a yeast population
on wheat depends on air temperature, humidity
and broad-spectrum fungicides (Captan). Although
the biological control agents we used in
this study were indigenous to the vineyard, their
efficient use and the number of times they should
be applied before harvest will depend on factors
affecting the physical and chemical microclimate.
Those affects must be determined in order to
improve their biocontrol efficacy.
The future use of biological agents for disease
control will depend greatly on the price of the
product, which, in turn, will depend on the ease of
growing the organism (Fokkema, 1996) and on
the dilution factor needed from culture to commercial
spray. When we worked with small clusters,
instead of checking the exact concentration
of the antagonist in suspension, we used a dilution
factor of 1:10 from the concentration at the stationary
phase of each antagonist. Different organisms
reach the stationary phase at different
concentrations and strains that can be effective at
a high dilution rate will be less expensive as
control agents.
Chemical control of grape decay is difficult
because of the diverse fungi involved. The chemicals
we used gave adequate control of B. cinerea
but only the newly registered fungicide
Pyrimethanil (applied in 1998) protected the
grapes from A. niger rot, the predominant fungus
on wine grapes. The antagonists, though less efficient
against this fungus, in most cases, reduced
the percentage of diseased clusters. One of the
problems with chemical control is the hazard to
the consumers and an IPM program combining
early chemical sprays, to reduce the level of fungal
inoculum, with antagonist application close to
harvest, could be the logical solution to benefit
consumers, growers and the environment.
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