Allelochemicals Biologica... - Name

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NANCY KOKALIS-BURELLE AND RODRÍGO RODRIGUEZ-KÁBANA component of Integrated Pest Management (IPM) programs, biopesticides can decrease
the use of conventional chemical pesticides (Halbrendt, 1996).
Increased restrictions on use and phase-out of chemical fumigants such as methyl
bromide and other chemical nematicides for control of plant-parasitic nematodes make
the discovery of target-specific, environmentally safe, naturally occurring biopesticide
compounds that suppress nematode populations or modify nematode behavior
increasingly important. For instance, allelochemicals that affect nematode chemotaxis
could be invaluable in many different scenarios for nematode control and represents
an area of research with both great needs for identification of active compounds, and
great possibilities for their use. The production of chemical cues by plants and
behavioral responses to these cues by nematodes are critical to successful host location
and reproduction in nematodes, which are highly dependent on these chemotactic
stimuli during many stages of their life cycles (Bridge, 1996; Huettel, 1986; Yasuhira
et al., 1982).
In order to make effective use of nonchemical or biochemical pest control strategies
such as allelochemicals for suppression of plant-parasitic nematodes, users need to be
familiar with the types and quantity of nematodes present in their soil and determine
the feasibility of growing a cover or rotation crop, using an organic amendment, or a
formulated biopesticide. Identification of cash crops that produce compounds capable
of reducing pathogenic nematode populations and that can be incorporated into existing
production regimes is rare (Gardner et al., 1992; Mojtahedi et al., 1993a; Halbrendt,
1996). Some notable exceptions to this include commercial production of Crotalaria,
mustard, African marigold, asparagus, and sesame in India (Bridge, 1996). The level
to which growers will employ the use of cover crops or rotation crops is ultimately
dependent on the economic feasibility of this method for nematode control. When
determining the economic feasibility of this approach, the additional benefits that
cover crops provide should be considered. These benefits include nitrogen fixation,
soil stabilization, and weed management (Halbrendt, 1996).
Many plant constituents and metabolites have been investigated for activity against
plant-parasitic nematodes. The conditions under which compounds are effective
against nematodes vary with the compounds (Ferris and Zheng, 1999; Zasada and
Ferris, 2004). These active compounds, or precursors of active compounds, can often
be applied to soil as organic amendments, or refined and developed as biopesticide
compounds.
Most allelochemicals are short-lived in soil as they are often easily metabolized
or hydrolyzed, and may require that plants are actively growing and secreting them
into the rhizosphere in order to be effective (Cheng, 1992). In some cases, breakdown
products of allelochemicals are the active components against nematodes (Borek
et al., 1995). Many such compounds are produced upon decomposition of plant material
that can be useful when incorporated into soil as green manures (Brown and Morra,
1997; Mojtahedi et al., 1991; 1993a, b; Prot et al., 1992; Zasada and Ferris, 2004). In
each of these instances, soil physical and chemical conditions, microbial populations,
and environmental conditions influence the retention, transformation and transport
of the allelochemicals (Cheng, 1992). Undoubtedly, these physical, microbiological,