Allelochemicals Biologica... - Name

ALLELOCHEMICALS FROM AGERATUM CONYZOIDES AND ORYZA SATIVA 197
Several flavones, ageratochromene and its two dimers were isolated and identified
from the A. conyzoides intercropped citrus orchard soil (Figures 2 and 3), their amounts
ranged from 11 to 93µg g -1 in the air dried soil. However, these chemicals could not be
found in the non-intercropped citrus orchard soil. The results showed that these
chemicals were primarily released from ground cover plants of A. conyzoides and
accumulated in the soil year by year.
A: R 1 =R 2 =OCH 3 ; B: R 1 =H, R 2 =OCH 3 ; C: R 1 =OCH 3 , R 2 =H
D: R 1 =R 3 =OCH 3 , R 2 =H; E: R 1 =R 2 =R 3 =OCH 3 ;
F: R 1 =R 3 =H, R 2 =OCH 3 ; G: R 1 =H, R 2 =R 3 =OCH 3 ;
H: R 1 =R 3 =OCH 3 , R 2 =OH; I: R 1 =R 3 =OCH 3 , R 2 =α- rhamnosyl.
Figure 2. Flavones produced and released from the A. conyzoides
intercropped citrus orchard soil.
Bioassays showed that ageratochoromene and flavones could significantly inhibit
spore germination of the pathogenic fungi P. citrophthora, P. aphanidermatum and F.
solani, but two dimers of ageratochromene had no inhibitory effects on them (Table
2). Thus, the flavones and ageratochromene could be one of the key factors that A.
conyzoides plants are able to reduce the populations of soil pathogenic fungi in the
citrus orchard. Two dimers, though not biologically active, may be the products of
ageratochromene transformation in soil.
Further studies revealed that ageratochromene underwent a reversible
transformation in the soils, that is, ageratochromene released from ground A.
conyzoides plants was transformed into its dimers, and the dimers can be
remonomerized in the soils (Kong et al., 2004c). However, this dynamic transformation
did not occur in the soil with low organic matter and fertility (Figure 3). The reversible
transformation between ageratochromene and its dimers in the A. conyzoides
intercropped citrus orchard soil can be an important mechanism maintaining bioactive