Agriculture Reference
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(±)-catechin. In contrast,
Agrobacterium radiobacter
was inhibited only by
higher concentrations (300 µg ml
−1
(+)-catechin or more), and
Agrobac-
terium rhizogenes
(15834) was not affected even by high (+)-catechin
concentrations (Bais et al. 2002). None of the bacteria were affected by
(-)-catechin treatment. Similarly, Veluri et al. (2004b) found that low con-
centrations of (+)-catechin (12.5−25 µg ml
−1
)inhibitedgrowthofseveral
root-colonizing fungi, including
Tricoder ma reesi
,
T. v iridi s
,
Fusarium oxys-
porum
,
Aspergillus niger
,and
Penicillium
sp. Veluri et al. (2004b) com-
pared the antimicrobial activity of several catechin derivatives and found
that (+)-catechin was the most active against
E. carotovora
,
E. amylovora
,
X. campestris
,and
A. radiobacter
, while the (+)-catechin derivatives (+)-
pentaacetylcatechin, (+)-tetramethoxycatechin, and (+)-isopropylidylcat-
echin showed less antimicrobial activity. (+)-Pentaacetylcatechin and (+)-
tetramethoxycatechin also inhibited some of the root-colonizing fungi.
Notably, (+)-catechin antibacterial activity may be limited to gram nega-
tive species (Veluri et al. 2004b). (+)-Catechin has no effect or only a very
weak effect on a number of gram positive human pathogens (Palma et al.
1999; Puupponen-Pimiš et al. 2001).
Although (-)-catechin does not appear to affect soil bacteria, (-)-catechin
does appear to inhibit other soil organisms. Specifically, recent studies con-
ducted in our laboratory have shown that (-)-catechin is nematicidal (B.
Prithiviraj and J. Vivanco, unpublished data). Addition of low concentra-
tions (1−10 g ml
−1
) of (-)-catechin to the growth medium resulted in 100%
mortality of the bacterial-feeding, saprophytic nematode
Caenorhbditis
elegans
in 3−4 days. No previous studies have reported (±)-catechin in-
hibition of plant pathogenic or saprophytic nematodes. Such nematidical
activity could have large effects on soil processes (discussed later) and on
soil microbial populations. Free-living nematodes in the soil are often bac-
terial or fungal feeders, and thus could influence population dynamics of
plant pathogens or mutualists.
In addition, soil fungi, and perhaps other soil microbes, may influence
(±)-catechin secretion by
C. maculosa
.Fungalcellwallsisolatedfromthe
soil-borne pathogen
Phytophthora cinnamommi
elicited increased root ex-
udation of (±)-catechin by
C. maculosa
(Bais et al. 2002).
C. maculosa
plants grown together in vitro produced approximately 83.2 µg ml
−1
of
(±)-catechin in their pooled root exudates. When
P. c i n n a m o n i
cell wall
isolates were applied to
C. maculosa
plants in vitro, the (±)-catechin con-
centration in the root exudates increased to 185.04 µg ml
−1
.Theresponse
of
C. maculosa
to fungal cell wall elicitors suggests that (±)-catechin may be
an inducible plant chemical defense, similar to phytoalexins, that
C. mac-
ulosa
secretes in larger quantities when under attack by pathogenic mi-
crobes in the rhizosphere. Both constitutive and induced (±)-catechin ex-
udation have the potential to affect the population dynamics of a wide
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