Allelochemicals Biologica... - Name

ALLELOCHEMICALS FROM AGERATUM CONYZOIDES AND ORYZA SATIVA
2.2 The essential oil of A. conyzoides and their biological activities on related
pathogens
A. conyzoides has a wide range of secondary metabolites including flavonoids,
chromenes, benzofurans and terpenoids. Among these secondary metabolites, some
are allelochemicals inhibiting the growth of other organisms (Okunade, 2002; Pari et
al., 1998). Usually, A. conyzoides can produce and release volatile chemicals into the
environment. The concentration of its released volatiles is so high that the unpleasant
odor can be smelled in the fields. Therefore, most investigations have focused on
chemical components of its essential oil (Albersberg and Singh, 1991; Ekundayo et
al., 1988; Menut et al., 1993; Wandji et al., 1996). It was found that ageratochromenes
and their derivatives, monoterpenes and sesquiterpenes were the major components
of the essential oil from A. conyzoides (Kong et al., 1999; 2002a; Pari et al., 1998).
The allelopathic potential of volatile allelochemicals from A. conyzoides has been
reported in our previous papers (Kong et al., 1999; 2002a; 2004a). Anti-microbial
effects of the essential oil from A. conyzoides have been confirmed for a long time
(Biond et al., 1993; Dixit et al., 1995; Rao et al., 1996). Table 1 showed that several
fungal pathogens, such as Rhizoctonia solani, Botrytis cinerea, Sclerotinia sclerotiorum,
were significantly inhibited by the essential oils of A. conyzoides (Kong et al., 2001;
2002a). The quantity and variety of allelochemical produced by A. conyzoides varies
depending on its growth stages and habitats and so do their growth inhibitory effects
on the pathogens (Kong et al., 2002a, 2004a). A. conyzoides produces different volatiles
in larger quantities when infected with Erysiphe cichoracearum (Kong et al., 2002a).
Table 1. Inhibitory effects of essential oil from the A. congzoides collected from
different growth stages and habitats on fungal pathogens.
The essential oil collected Pathogens
from R. solani B. cinerea S. sclerotiorum
Growth stages
4-leaf 23.8±3.8a 19.6±5.3a 39.8±7.6a Pre-flowering 56.3±10.1b 49.7±9.1b 60.2±7.9b Peak-flowering 100c 82.3±11.5c 100c Mature 60.6±8.8b 58.3±7.4b 40.8±9.5a Habitats
Cultivated field 79.6±10.2d 83.5±6.3c 93.8±7.7c Under citrus canopy 58.4±4.3b 45.6±6.1b 66.2±5.5b Roadside 100 c 100d 100c Control
50% Carbendazin 100c 59.8±5.2c 92.3±7.9c Test concentrations of the essential oil were 100 µg/ml. All data are inhibitory percentage of spore germination
of fungal pathogens tested and mean of 3 replicates with standard error. Data in a column not followed by the
same letter are significantly different, p=0.05, ANVOA with Ducan’s multiple range test.
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