Allelochemicals Biologica... - Name

3.1. Brassicaceae
ALLELOCHEMICALS : MANAGEMENT OF PLANT-PARASITIC NEMATODES 21
3. GREEN MANURES AND ORGANIC AMENDMENTS
Glucosinolates are compounds produced by many members of the Brassicaceae plant
family including mustard, rape, canola, and cabbage (Fahey et al., 2001). These
compounds are β-D-thioglucosides with differing organic side chains, and can be
aliphatic, aromatic, or indole forms. Enzymatic degradation of glucosinolates produces
several types of compounds including isothyocyanate (ITC), a well known nematicide
(Brown and Morra, 1997).
Glucosinolates are produced in various levels throughout the plant and to different
degrees among plant species (Fahey et al., 2001). In studies by Potter et al. (1998) the
nematicidal potential of Brassica spp. leaf and root tissue differed, with leaf tissue
being far more toxic to P. neglectus than root tissue. However, leaf tissue toxicity was
not correlated with either total glucosinolate content or with any individual
glucosinolate, while the suppression achieved with the addition of root tissue was
highly correlated with levels of 2-phenylethyl glucosinolate within roots (Potter et
al., 1998). Zasada and Ferris (2004) performed studies where levels of glucosinolates
in various Brassica spp. were determined and amendments containing equivalent
amounts of active compounds were compared to determine their efficacy in controlling
M. javanica and Tylenchulus semipenetrans. They determined that the degradation
of brassicaceous amendments in soil resulted in a series of biological and chemical
processes that differed among plant species. It was also determined that consistent
nematode suppression could be achieved using brassicaceous amendments if the
chemical composition of the organic material was considered and appropriate levels
of biomass applied (Zasada and Ferris, 2004).
3.2. Neem (Azadirachta indica)
The neem tree is a tropical evergreen tree native to India whose biologically active
properties have been recognized in Asia for centuries (Thakur et al., 1981). During
the past 30 years, interest in the extensive variety of biologically active compounds
produced by neem has increased. Various parts of the neem plant including leaves,
seeds and bark, produce over 40 active diterpenoid, triterpenoid, limonoid, and
flavonoid compounds, with a wide range of nematicidal activity (Bhatnagar and
Goswami, 1987). The most well known and active compounds produced by neem are
the azadirachtins (Thakur et al., 1981).
Nematode control has been achieved following the incorporation of neem products
into soil, and their subsequent decomposition and release of nematicidal compounds
(Stirling, 1991). Numerous studies have shown that leaves and oilcake of neem are
effective in controlling M. incognita and increasing growth and yield of vegetable
crops when used as a soil amendment (Akhtar, 1998; Bhatnagar and Goswami, 1987).
This effect has also been reported to persist in successive crops (Akhtar and Alam,
1991; Akhtar and Mahmood, 1996). Neem based products have also shown nematicidal