Allelochemicals Biologica... - Name

MARK A. BERNARDS 1 , LINA F. YOUSEF 1 , ROBERT W. NICOL 2
THE ALLELOPATHIC POTENTIAL
OF GINSENOSIDES
1
Department of Biology, University of Western Ontario, London,
2
ON, Canada, N6A 5B7
NovoBiotic Pharmaceuticals, Cambridge MA, 02138, USA
Email: bernards@uwo.ca
Abstract. American ginseng (Panax quinquefolius L.) is a perennial herb valued for the medicinal properties
of its large, fleshy tap root. These medicinal properties are purported to be due to the triterpenoid saponins, or
ginsenosides, that accumulate to 3-6% of the root dry weight. We asked the question: what is the ecological role
of ginsenosides in Panax species? In addressing this question, we have determined that ginsenosides, like other
saponins, possess fungitoxic properties, although different fungi and oomycotan organisms appear to be
differentially affected by them in vitro. In order to play an allelopathic role, however, ginsenosides must be
present in the soil at biologically active (i.e., ecologically relevant) concentrations. Results to date support the
hypothesis that ginsenosides are phytoanticipins and serve as host resistance factors. The success of certain
pathogens (e.g., Pythium cactorum, Pythium irregulare, Cylindrocarpon destructans) on ginseng may arise
from their ability to detoxify or otherwise utilize ginsenosides as a nutritive source or growth stimulating factor,
while other soil borne organisms appear susceptible to their fungitoxic properties. Ginsenosides have been
isolated from rhizosphere soil and root exudates suggesting that these compounds are involved in allelopathic
interactions between the host plant and soil fungi. Ultimately this allelopathic interaction may influence the
fungal diseases of ginseng.
1. INTRODUCTION
American ginseng (Panax quinquefolius L.) produces triterpenoid saponins called
ginsenosides, which are slowly released into the rhizosphere. Ginsenosides, like other
saponins, are fungitoxic, and as such may modify the balance of microorganisms in
the soil; i.e., they are potentially allelopathic. From a disease management point of
view, the extent to which ginsenosides alter the soil microbial community may have
profound consequences, especially when disease causing organisms are favoured in
the new balance. Understanding how ginsenosides affect soilborne microbes is important
in understanding disease cycles in this crop.
2.1. Saponins
2. SAPONINS
Saponins, are glycosylated natural products with surfactant and soap-like properties
that tend to froth in aqueous solution, even at low concentration (Dewick, 1997).
157
Inderjit and K.G. Mukerji (eds.),
Allelochemicals: Biological Control of Plant Pathogens and Diseases, 157– 175.
© 2006 Springer. Printed in the Netherlands.