Tuesday, August 4, 2009: 2:10 PM
Grand Pavillion II, Hyatt
Background/Question/Methods Upon herbivore attack, plants rely on a matrix-like type of responses, generally involving direct and indirect defenses. Direct defenses can act by physical or chemical means, via toxic or antinutritive effects; indirect defenses typically act by providing rewards or cues for predators or parasitoids to locate their host herbivores (e.g., volatile organic compounds or extrafloral nectar). Belowground, the release of terpenoid volatiles in the soil has been shown to attract entomopathogenic nematodes foraging for herbivorous insect larvae. In the milkweeds (Asclepias spp.), plants are predominantly defended in the shoots by the production of cardenolides and latex, whereas belowground mainly by cardenolides. Despite the fact that larvae of the specialist beetle Tetraopes tetraophthalmus are major herbivores of Asclepias syriaca, little was previously known about root defenses in the common milkweed. In common garden experiments, we tested whether insect damaged A. syriaca roots attract more nematodes than undamaged plants. We then analyzed volatile organic compounds from roots of damaged and undamaged plants. Finally, by screening and selecting milkweed genotypes for high and low root cardenolides, we examined the relationship between allocation to cardenolides and indirect defense in the roots.
Results/Conclusions
Results/Conclusions