Allelochemicals Biologica... - Name

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ANA LUISA ANAYA
production and release over time. A new challenge that exists for future plant scientists
is to generate additional information on allelochemical mechanisms of release,
selectivity and persistence, mode of action, and genetic regulation. In this manner, it
is possible to further protect plant biodiversity and enhance weed management
strategies in a variety of ecosystems.
Ohno et al. (2000) based on previous studies that suggested phenolics from legume
green manures may contribute to weed control through allelopathy, investigated if
red clover (Trifolium pratense) residue amended field soils expressed phytotoxicity to
a weed species, wild mustard (Sinapis arvensis). Field plots involving incorporation
treatments of wheat (Triticum aestivum) stubble or wheat stubble plus 2530 kg ha(-1)
red clover residue, were sampled at -12, 8, 21, 30, 41, 63, and 100 days after residue
incorporation (DAI). Soil-water extracts (1:1, m:v) were analyzed for plant nutrients
and phenolic content. Phytotoxicity of the extracts was measured using a laboratory
wild mustard bioassay. There was a 20% reduction of radicle growth in the green
manure treatment in comparison with the wheat stubble treatment, but only at the
first sample date after residue incorporation (8 DAI). The radicle growth reduction
had the highest correlation with the concentration of soluble phenolics in the soil,
water extracts. Bioassays using aqueous extracts of the clover shoots and roots alone
predicted a radicle growth reduction of 18% for the quantity of clover amendment
rate used in the field plots. The close agreement of the predicted and observed root
growth reduction at 8 DAI further supports clover residue as the source of the
phytotoxicity.
The allelopathic influence of sweet potato cultivar ‘Regal’ on purple nutsedge
was compared to the influence on yellow nutsedge under controlled conditions. Purple
nutsedge shoot dry weight, total shoot length and tuber numbers were significantly
lower than the controls (47, 36, and 19% inhibition, respectively). The influence on
the same parameters for yellow nutsedge (35, 21, and 43% inhibition, respectively)
was not significantly different from purple nutsedge. Sweet potato shoot dry weight
was inhibited by purple and yellow nutsedge by 42% and 45%, respectively. The
major allelopathic substance from ‘Regal’ root periderm tissue was isolated and tested
in vitro on the two sedges. The I 50 ’s for shoot growth, root number, and root length
were 118, 62, and 44 µg/ml, respectively, for yellow nutsedge. The I 50 ’s for root number
and root length were 91 and 85 µg/ml, respectively, for purple nutsedge and the I 50 for
shoot growth could not be calculated (Peterson and Harrison, 1995). These allelopathic
substances, the resin glycosides mixture extracted from the periderm tissue of storage
roots from sweet potato, Ipomoea batatas, was bioassayed for effects on survival,
development, and fecundity of the diamondback moth, Plutella xylostella. The resin
glycoside was incorporated into an artificial diet and fed to P. xylostella larvae. First
instars were placed individually into snap-top centrifuge vials containing artificial
diet with one of six concentrations of resin glycoside material (0.00. 0.25, 0.50, 1.00,
1.50, and 2.00 µg/ml). Each replication consisted of 10 individuals per concentration,
and the experiment was repeated 13 times. Vials were incubated at 25 o C and a
photoperiod of 14:10 (L:D) h in a growth chamber. After 6 d, surviving larvae were
weighed and their sex determined, then returned to their vials. Later, surviving pupae