Allelochemicals Biologica... - Name

4.5. Citral
ALLELOCHEMICALS : MANAGEMENT OF PLANT-PARASITIC NEMATODES 25
Citral, is the aldehyde of geraniol, and occurs in the volatile oils of lemon grass,
lemon, orange, limetta, and pimento (Harborne and Baxter, 1993). The flavor of
lemon oil is largely due to its citral content, and the pure aldehyde may be used to
increase the flavoring power of commercial samples of that oil (Harborne and Baxter,
1993). In research trials evaluating the nematicidal potential of citral compared to
other allelopathic chemicals, citral was less nematicidal against M. incognita juveniles,
and more phytotoxic to tomato than benzaldehyde in vitro, and when added to a peatbased
potting mix (Kokalis-Burelle et al., 2002). When tested in vitro against rootknot
nematode eggs, citral reduced egg viability by 80%, but also decreased tomato
seed germination and growth in greenhouse trials (Kokalis-Burelle et al., 2002).
However, when evaluated in soil, citral reduced populations of root-knot nematode
juveniles, galling on roots, and increased cotton growth when applied at 0.1 -0.5 ml/
kg soil in the greenhouse, and at 0.18 -2.14 ml/kg soil in field microplots with no
phytotoxicity to cotton (Bauske et al., 1994). This difference in phytotoxicity may be
due to the difference in host plants tested or to the presence of microorganisms in soil
compared to the relatively uncontaminated conditions that occur in vitro and in potting
media.
5. CONCLUSIONS
The use of allelopathic compounds in either their native, degraded, or processed forms
for plant-parasitic nematode management is receiving increased attention as
agricultural producers face increasing restrictions on chemical biocides and
nematicides. Allelochemicals are classified as biochemical pesticides and have been
shown to possess various levels of activity against a wide range of plant-parasitic
nematodes, while exhibiting reduced toxicity to nontarget species and reduced
persistence in soil. The fact that some allelochemicals can be produced in large
quantities in plant material and incorporated into soil as green manures or organic
amendments increases their potential for use as components of nematode management
strategies. The wide array of plant families that produce nematicidal or nematistatic
compounds provides almost unlimited research opportunities for discovery of novel
compounds. Determination of the mechanisms responsible for nematode suppression
with allelopathic compounds also represents a research area with exciting possibilities.
In order to improve the nematicidal and nematistatic efficacy achieved with allelopathic
compounds, a greater understanding of the effects of soil microbiology, soil properties
and environmental conditions on the active compounds is necessary. Currently
available application methods need to be refined and new and improved methods
developed to enhance the performance of allelochemicals for nematode control. Further
investigation is also needed to develop compatible companion applications of
biochemical pesticides and biological control agents, to determine the effects of
allelochemicals on nematode nervous systems, and how they act as nematode attractants
and/or repellents. This research area has enormous potential for discovery of new