Two herbivore-deterrent iridoid glycosides reduce the in-vitro growth of a specialist but not of a generalist pathogenic fungus of Plantago lanceolata L |
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| Authors: | Hamida B Marak Arjen Biere Jos MM van Damme |
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| Institution: | (1) Department of Plant Population Biology, Netherlands Institute of Ecology, NIOO-KNAW, Centre for Terrestrial Ecology, P.O. Box 40, NL-6666 ZG Heteren, The Netherlands, NL |
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| Abstract: | Summary. Many secondary plant compounds are involved in defense against both insect herbivores and pathogens. Two secondary plant
compounds of Plantago lanceolata, the iridoid glycosides catalpol and its precursor aucubin, are well known for their deterrent effects on generalist and
non-adapted specialist insect herbivores. We tested the effects of these compounds on the in-vitro growth of a specialist
and generalist fungal pathogen of this host species. Two chemical forms of these iridoids were tested. The glycosides and
their aglycones, the products of enzymatic conversion by specific $/Beta$-glucosidase enzymes. The glycosides enhanced growth
of both the specialist fungus Diaporthe adunca and the generalist fungus Fusarium moniliforme var. subglutinans. The positive effect of these glycosides on the generalist fungus is in sharp contrast with the generally negative effects
of these glysosides on generalist insect herbivores. The aglycones of aucubin and catalpol reduced the growth of the specialist
fungus D. adunca, but, contrary to expectation, enhanced the growth of the generalist fungus F. moniliforme var. subglutinans. Effects of aucubin on D. adunca were stronger than effects of catalpol. This was true both for the growth stimulating effects of the glycosides and for the
fungitoxic effects of the aglycones. We therefore expect that the effects of these iridoids in P. lanceolata on the specialist fungus will strongly depend on the ratio between catalpol and its precursor aucubin and the chemical form
(glycoside or aglycone) in which these compounds are encountered by the fungus during growth. Our results suggest that iridoid
glycosides in P. lanceolata can be used as defense against both herbivores and pathogens, but that their effects are highly specific with respect to
the natural enemy species that is encountered.
Received 11 April 2002; accepted 9 August 2002 |
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| Keywords: | , Chemical defense —, plant-pathogen interactions —, iridoid glycosides —, aucubin —, catalpol —, Diaporthe adunca —, Fusarium,,,,,moniliforme —, Plantago lanceolata |
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