Constraints of Simultaneous Resistance to a Fungal Pathogen and an Insect Herbivore in Lima Bean (<Emphasis Type="Italic">Phaseolus lunatus</Emphasis> L.) |
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Authors: | Daniel J Ballhorn |
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Affiliation: | (1) Department of Plant Biology, 250 Biological Sciences Center, University of Minnesota, 1445 Gortner Avenue, St. Paul, MN 55108, USA |
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Abstract: | The existence of tradeoffs among plant defenses is commonly accepted, however, actual evidence for these tradeoffs is scarce.
In this study, I analyzed effects of different direct defenses of wild lima bean plants (Phaseolus lunatus) that were simultaneously exposed to a fungal pathogen (Colletotrichum lindemuthianum) and an insect herbivore, the Mexican bean beetle (Epilachna varivestis). Although plants were derived from spatially widely separated populations, I observed a common tradeoff between resistance
to pathogens and herbivores. Plants with high levels of anti-herbivore defense (cyanogenesis) showed low levels of resistance
to pathogens (polyphenol oxidase activity and phenolic compounds), and vice versa. Competition for resources generally is considered to be the basis for tradeoffs. However, I report direct inhibition of
polyphenol oxidase by cyanide, making simultaneous expression of both defenses at high levels impossible. I argue that populations
composed of individuals investing in one type of defense have an advantage in environments that periodically favor either
pathogen or herbivore plant antagonists. |
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