Allelochemicals Biologica... - Name

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ANA LUISA ANAYA
organic matter incorporation should lead to increased trapping of plant-parasitic
nematodes (Wang, 2000).
Soil amended with C. juncea to give a 1:100 (w:w) concentration, enhanced
parasitic nematode-trapping fungi, nematode egg parasitic fungi, vermiform stage
parasites, and bacterivorous nematode population densities more efficiently than soil
amended with chopped pineapple tissues or non-amended soil. Crotalaria juncea
amendment enhanced the population densities of nematode-trapping fungi and the
percentage of eggs parasit-ized by the fungi. Enhancement of nematode-trapping fungi
was most effective in soils that had not been treated with 1,3-dichloropropene for at
least 5 months. Suppression of R. reniformis by C. juncea amendment was correlated
with parasitic nematode-trapping fungi, fungal egg parasites, and bacterivorous
nematodes. Nematode-trapping fungi population densities were higher in C. juncea
planted plots than weed fallow plots. However, four months after removal of C. juncea,
and replacement with pineapple plants, the population densities of nematode-trapping
fungi greatly decreased (Wang, 2000).
Suppressive cropping systems rely on the use of precisely defined sequences of
crops to increase populations and activities of naturally occurring antagonistic
microorganisms in soil. Some crops such as velvetbean (Mucuna deerengiana) produce
compounds which are directly toxic to nematodes and stimulate microbial antagonism
to plant parasitic nematodes. These ‘active’ crops when included in cropping systems
can increase suppressiveness of the system against nematodes. There are a number of
active crops throughout the world which can be used in a practical manner to enhance
naturally occurring biological control of plant parasitic nematodes (Wang, 2000)
Rich and Rahi (1995) conducted two greenhouse trials to determine the influence
of ground seed of castor (Ricinus communis), crotalaria (Crotalaria spectabilis), hairy
indigo (Indigofera hirsuta), and wheat (Triticum aestivum) on tomato (Lycopersicon
esculentum) growth and egg mass production of Meloidogyne javanica (test 1) or M.
incognita (test 2). Ground seed from each plant species was individually mixed with
an air-dried, fine sandy soil at rates of 0, 0.5, 1.0, and 2.0% (w/w). The mixtures were
placed in one-liter plastic pots, and water was added to bring soil to field capacity.
After ten days, 0 or 10 000 M. javanica or M. incognita eggs and juveniles were
added to each pot. A single ‘Homestead’ tomato seedling was transplanted into each
pot and allowed to grow for 70 days in test 1 and 75 days in test 2. Compared to the
non-amended control, egg mass production was significantly reduced by all treatments
except the 0.5% levels of wheat and castor and the 1.0% castor treatment. The 2.0%
levels of ground seed of Crotalaria and hairy indigo almost completely suppresses
egg mass production of both M. javanica or M incognita. With the exception of the
1% Crotalaria treatment in test 2, total plant weight did not differ between treatments
and the control.
Morris and Walker (2002) mixed dried ground plant tissues from 20 leguminous
species with Meloidogyne incognita-infested soil at 1, 2 or 2.5, and 5% (w/w) and
incubated for 1 week at room temperature (21 to 27 0 C). Tomato (‘Rutgers’) seedlings
were transplanted into infested soil to determine nematode viability. Most tissues