Agriculture Reference
In-Depth Information
For example, there is a body of research for the feasibility of using organic amendments
to create conditions and microbial responses to suppress soilborne diseases naturally.
Similarly, breeding or insertion of transgenic genes in crop plants could, as described,
provide the means for a crop to signal native populations for the appropriate response.
At the same time, there likely may need to be engineered rhizospheres that provide the
habit and energy to enable native subpopulations to proliferate and respond at levels that
are agronomically significant. For example, there is evidence from pure culture work that
free-living or endophytic diazotrophs have high potential to fix N, but under field condi-
tions these organisms are severely limited by C or energy availability. Such an approach
would only require the introduction of new cultivars into existing systems—with minimal
technical support and reducing the need for external inputs or inoculations.
Biofilms are another important but poorly understood soil/rhizosphere habitat that
could be important and related to this discussion. In this case, an assemblage of heteroge-
neous microcolonies (e.g., protozoans, fungi, nematodes, and prokaryotes) is encapsulated
in EPSs. These organisms can work in consortia to perform biogeochemical processes or
cooperatively to aid individual microorganisms. There is now speculation that biofilms
have complex cell-cell signaling and physical structures such as water channels to dis-
perse nutrients, metabolites, and waste products and “nanowires” that transfer energy.
Understanding biofilms and diversity and potential interactions of their microbial com-
munities could provide the basis for designing or stimulating certain biofilm communi-
ties that can exist in more stable and interconnected members with diverse services for
plants. Although an engineered plant-microbial system offers great potential, there must
be collaborative and parallel research on cropping system management within a regional
and farm-level/cropping systems context. This includes the appropriate cultural practices
associated with the use of specific organisms for a given agricultural service. If bioengi-
neered technologies are developed in isolation of a social, economic, and agroecosystems
context, past experience would suggest this greatly diminishes the potential for imple-
mentation and adoption of these systems in farmers' fields. Furthermore, the need for
these broader considerations is that biologically based systems are much more sensitive to
environmental controls than agricultural systems based on chemical and external input.
In summary, there are exciting research approaches that offer the possibility to
develop crop rhizospheres with a consortium of microbial species that support, pro-
tect, and enhance the yield and quality of crops. To attain this goal, considerable
fundamental research is needed on microbial and rhizosphere ecology, cell-to-cell
communications, and microbial genomics and proteomics in combination with crop-
ping systems research.
References
Abbasi, P. A., J. Al-Dahmani, F. Sahin, et al. 2002. Effect of compost amendments on disease severity
and yield in organic and conventional tomato production systems.
Plant Dis.
86:156-161.
Alvarez, B., G. Martínez-Drets, and B. Alvarez. 1995. Metabolic characterization of
Acetobacter diazo-
trophicus
.
Can. J. Microbiol.
41:918-924.
Alvarez, M. I., R. J. Sueldo, and C. A. Barassi. 1996. Effect of
Azospirillum
on coleoptile growth in
wheat seedlings under water stress.
Cereal Res. Commun.
24:101-107.
Amara, M. A. T., and M. S. A. Dahdoh. 1997. Effect of inoculation with plant growth promoting rhi-
zobacteria (PGPR) on yield and uptake of nutrients by wheat grown on sandy soil.
Egyptian J.
Soil Sci
. 37:467-484.
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