Generalized plant defense: effects on multiple species

Abstract

Two species of lepidopteran herbivores, Manduca sexta (Sphingidae) and Trichoplusia ni (Noctuidae), were reared on synthetic diet containing either the alkaloid nicotine or the flavonoid rutin. Survival and pupal weight of the specialist M. sexta did not differ when larvae were reared on diet containing nicotine or rutin. In contrast, the generalist T. ni did not survive on diet containing 0.125% nicotine or greater, whereas larvae survived on all concentrations of rutin. These data demonstrate that the alkaloid nicotine is inhibitory toward generalist, but not specialist herbivores, whereas the flavonoid rutin has no effect on specialist herbivores and limited effects on generalist herbivores. Five species of Pseudomonas bacterial pathogens: P. syringae, P. syringae pv. angulata, P. syringae pv. tabaci, P. fluorescens, and P. solanacearum were grown on nutrient agar containing nicotine or rutin at concentrations ranging from 0.0 to 1.0% wet weight in 0.1% intervals. No species of Pseudomonas grew at concentrations greater than 0.5% nicotine when 10 colony forming units (cfu) were used, but growth occurred at all concentrations of rutin when 10 cfu were used. These data indicate that nicotine was inhibitory to growth of both herbivores and pathogens, suggesting that certain plant secondary chemicals with high toxicity are of a generalized nature and affect multiple species. Differences in the sensitivity of organisms to allelochemicals such as generalist or specialist can make it appear that specific allelochemicals affect specific organisms, when in fact it is the tolerance of the organism to the plant chemical that is responsible. In four separate studies, the growth of M. sexta, T. ni and Helicoverpa zea was significantly lower on plants inoculated with P. solanacearum. Alteration in leaf quality by P. solanacearum was due to either reductions in leaf nutrients or increases in allelochemicals. We speculate that localized or systemic induction by both herbivores and pathogens can cause changes in leaf quality, effecting each other's subsequent colonization. The generalized nature of plant secondary compounds and potential reciprocal effects on induction by both species suggests that herbivores and pathogens may affect plant quality through induction and diffuse interactions of disparate species can alter the community of organisms colonizing a plant.

Rapid phlorotannin induction and relaxation in five Washington kelps

“…This response might decrease indirect damage due to herbivory, the loss of tissue due to breakage at grazer-weakened places in the thallus (Lowell et al 1991). Third, and perhaps most important evolutionarily, induced resistance in plants is characterized by low specificity of the organisms 'targeted' by the chemicals (Karban & Myers 1989, Krischik et al 1991, but see Stout et al 1997). Although we measured only one 'symptom' of induction (phlorotannins), induced responses may incorporate many traits that affect a range of herbivores or pathogens, creating a chang~ng and heterogeneous target to which predators are less likely to adapt (Karban & Myers 1989).…”

Macroevolution and the biological diversity of plants and herbivores

“…Probably the question of the incidence of pairwise versus diffuse defense evolution will vary with factors such as plant organ (e.g., fruit vs. leaf), defense type, and herbivore diet breadth. Even crude measures of the toxicity or deterrent effects of specific compounds across a wide array of insects appear to be rather rare, and those few suggest that effects are not highly correlated across herbivores (53)(54)(55). Genetic correlations of resistance of whole plants against various herbivores are also rather low (56)(57)(58), but these correlations, across genotypes that vary in many characters, may say little about the cross-effectiveness of any one defense character.…”

Two herbivore-deterrent iridoid glycosides reduce the in-vitro growth of a specialist but not of a generalist pathogenic fungus of Plantago lanceolata L

“…In some cases, the same chemical form of the secondary plant metabolite is responsible for its broad effects on the performance of pathogens and insects. Examples are the glycoalkaloid tomatine in tomato, the alkaloid nicotine and the flavonoid rutin in tobacco (Roddick 1974;Krischik et al 1991). In other cases, the effects of secondary plant compounds on different groups of organisms can be attributed to changes in their chemical structure, for instance following enzymatic hydrolysis (Fleming et al 1973;Schönbeck & Schlösser 1976;Kubo et al 1985;Hammerschmidt and Schultz 1996).…”