Agriculture Reference
In-Depth Information
The field of metagenomics is providing the tools to study not only what culturable
and non-culturable organisms are present, but to also answer questions about the met-
abolic activity and function of different microbial groups (Simon and Daniel
2011
).
Metagenomics generates largely unbiased samples from the environment of all genes
from all the members of the microbial communities present. This approach has po-
tential to identify and predict factors associated with disease suppression. It cannot
show which of these processes are active; however, the extraction and analysis of
metagenomic mRNA (the metatranscriptome) can provide information on the regula-
tion and expression profiles of complex communities (Simon and Daniel
2011
).
The following represents a preliminary list of hypotheses to be addressed or to
be tested further for additional host-pathogen interactions and/or for a wider range
of production and application environments:
• A consistently pathogen-suppressive ACT can be produced using immature com-
post produced by a wide range of variable raw ingredients within a defined C:N
ratio
• The addition of certain additives or organic adjuvants to compost tea can im-
prove the extent of disease suppression
• The presence of nitrate or other metabolic substrates in compost tea influences
its capacity to suppress leaf and fruit pathogens by supporting saprophytic and/
or pathogenic microorganisms on the leaf or fruit surface
• Components of compost tea can sometimes induce host resistance or influence
host tissue physiology in a way that can be characterised and related to the extent
of plant pathogen colonisation
• Microbial communities of immature or mature compost can be identified and
components correlated to the disease-suppressive qualities of an associated com-
post tea
• Some microbial taxa in compost tea survive on plant surfaces under conditions
in which other taxa would perish. If so, these taxa can be identified and their di-
versity and persistence under a range of conditions can be quantified in relation
to the level of disease suppression observed
• There is a relationship between the functional and metabolic diversity of micro-
bial communities in compost tea and disease suppression in the field
• Microbial communities present naturally on plant surfaces influence crop quality
(fresh or processed) and these communities can be modulated through applica-
tion of compost tea.
9.10
Conclusion
Compost teas are like any other form of biological control in that single or mul-
tiple applications rarely provide 100 % crop protection. Whereas the persistence and
growth of single microbial species used for biological control can be constrained
by sub-optimal conditions of UV radiation, temperature, humidity, rainfall, nutrient
availability and mechanism of action, evidence is needed to support the claim that
