Allelochemicals Biologica... - Name

ALLELOCHEMICALS : MANAGEMENT OF PLANT-PARASITIC NEMATODES 23
group of glucosinolate compounds extracted from rapeseed exhibited various levels
of nematicidal activity depending on concentration and length of exposure (Lazzeri
et al., 1993).
Later studies by Borek et al. (1995) investigated the persistence of glucosinolatederived
allyl isothiocyanate and allylnitrile in six soils. They found that the two
compounds differed with respect to the temperature, moisture conditions, and soil
physical conditions that effected their transformation in soil, and that both compounds
dissipated from soil at relatively rapid rates. Donkin et al. (1995) studied the toxicity
of glucosinolates and their enzymatic breakdown products to Caenorhabditis elegans.
They found that allyl isothyocyanate, one of the decomposition products of the
glucosinolate sinigrin, was three times more toxic to the nematode C. elegans than
corresponding glucosinolate itself.
4.2. Benzaldehyde (benzoic aldehyde)
Benzaldehyde occurs in seeds of bitter almond (Prunus dulcis). It is found naturally
in several cyanogenic glucosides and is used in food and fragrances for its almondlike
aroma and flavor (Harborne and Baxter, 1993). The value of benzaldehyde as a
fungicide is well established (Flor, 1926), with the nematicidal activity more recently
demonstrated. Benzaldehyde reduced populations of M. incognita in field microplots
with no phytotoxicity to cotton at 0.18 -2.14 ml/kg soil (Bauske et al., 1994). The
combination of chitin and benzaldehyde added to peat-based potting mix improved
tomato transplant growth and reduced galling by M. incognita in greenhouse trials
(Kokalis-Burelle et al., 2002). When tested in vitro against M. incognita eggs,
benzaldehyde was 100% effective as an ovicide for this species of root-knot nematode
(Kokalis-Burelle et al., 2002).
The direct effect of benzaldehyde on C. elegans chemotaxis kinetics was analyzed
by Nuttley et al. (2001). An initial attractive response to 100% benzaldehyde was
reported, followed by a strong aversion to the chemical. They determined this behavior
to be mediated by two genetically separable response pathways. Initially, upon
exposure, the attraction response dominates but eventually gives way to a repulsive
response. Oka (2001) found that with juveniles of M. javanica, immobilization and
hatching inhibition in vitro were greater with benzaldehyde and furfural than with
several other essential oils. Benzaldehyde and furfural also reduced galling on tomato
in pot experiments where other aldehydes were not effective (Oka, 2001).
The effects of benzaldehyde combined with several organic amendments on soil
microbial populations and plant-parasitic and nonparasitic nematodes were investigated
by Chavarría-Carvajal et al. (2001). They found that benzaldehyde combined with
most organic amendments reduced damage from parasitic nematodes and selected for
predominantly gram-positive rhizosphere bacteria. When benzaldehyde was combined
with root-knot nematode egg parasitizing isolates of the fungus Fusarium solani,
increasing rates of benzaldehyde in soil reduced nematode penetration and infection
of the host plant, and resulted in increased parasitism of M. javanica females by the
fungus (Siddiqui and Shaukat, 2003). However, the increasing rates of benzaldehyde