Allelochemicals Biologica... - Name

ALLEOPATHIC ORGANISMS AND
MOLECULES
selected for this study were p-hydroxybenzoic acid, ferulic acid, umbelliferone, catechin,
emodin, 1,8-cineole, carvone, and betulin. Lettuce (Lactuca sativa L.) was used as
test species for agar gel and soil growth bioassays. Root and shoot growth of lettuce
was inhibited for all the above except emodin and catechin. However, in soils treated
with different phenolics and terpenoids, only root growth of lettuce was inhibited,
whereas shoot growth was promoted. Recovery of p-hydroxybenzoic acid and
umbelliferone was higher in unautoclaved soils, while that of catechin was lower.
Nava-Rodriguez et al. (in press) observed the in vitro effects of aqueous leachates
from fresh and dry, flowering and vegetative stage of Phaseolus species, faba bean,
alfalfa, vetch, maize, and squash, and weed species on the root growth of selected
crop and weeds, as well as on two strains of Rhizobium leguminosarum biovar phaseoli
(CPMex1 and Tlaxcala). Most of the specimens were collected in a traditional
agricultural drained field (“Camellon”) in Tlaxcala, Mexico where maize, beans,
squash, alfalfa, faba-beans, and vetch are cultivated in mixed or rotation crops.
Significant effects of leachates from fresh vegetative and flowering cultivated plants
and weeds were predominantly stimulatory on the growth of tested crops, being the
leachates from fresh aerial parts of alfalfa and pinto bean the most stimulatory.
Nevertheless, aqueous leachates from fresh and dry cultivated legumes (vegetative
and flowering) inhibited the growth of weeds. In contrast, the aqueous leachates from
the dry aerial part of almost all plants resulted inhibitory on the root growth of the test
crops, except maize. Aqueous leachates were also evaluated on the growth of two
strains of Rhizobium leguminosarum biovar phaseoli. Leachates from some of the
tested crops significantly stimulated the growth of both Rhizobium strains. The aqueous
leachates from fresh aerial parts of the weeds Simsia amplexicaulis and Tradescantia
crassifolia significantly inhibited the growth of CPMex1 Rhizobium strain. On the
other hand, the aqueous leachates from fresh roots of these same weeds inhibited the
growth of the Tlaxcala strain. In preliminary chemical tests using thin layer
chromatography (TLC), phenolics were detected in dry aerial parts of vegetative alfalfa,
pinto bean, and vetch, and dry aerial part of flowering faba bean suggesting the role
of these compounds in the allelopathic effects of these legumes.
Nilsson et al. (1998) reported on the temporal variation of phenolics and a
dihydrostilbene, batatasin III, in Empetrum hermaphroditum leaves. These authors
reported that first year shoots produced higher levels of phenolics than older tissues.
High phenolic concentration was maintained through the second year, but it declined
afterwards. However, the phytotoxicity of E. hermaphroditum extracts was related
more to batatasin III than phenolics.
Hyder et al. (2002) performed a study focused on the presence and distribution of
secondary phenolic compounds found within creosotebush (Larrea tridentata). Total
phenolics, condensed tannins and nordihydroguaiaretic acid (NDGA) were measured
in nine categories of tissue within creosotebush. Total phenolic and condensed tannin
concentrations were determined using colorimetric methods while NDGA content
was determined with high performance liquid chromatography (HPLC). Phenolics
were present throughout the plant with the highest concentrations in green stems
(40.8 mg/g), leaves (36.2 mg/g), and roots (mean for all root categories=28.6 mg/g).
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