Cotton Plant, Gossypium hirsutum L., Defense in Response to Nitrogen Fertilization |
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Authors: | Yigen Chen Eric A. Schmelz Felix Wäckers John R. Ruberson |
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Affiliation: | (1) Department of Entomology, Michigan State University, East Lansing, MI 48824, USA;(2) Center of Medical, Agricultural, and Veterinary Entomology, USDA Agricultural Research Service, 1600/1700 Southwest 23rd Drive, Gainesville, FL 32608, USA;(3) Centre for Sustainable Agriculture, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK;(4) Department of Entomology, University of Georgia, Tifton, GA 31793, USA |
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Abstract: | Plants respond to insect herbivory by producing dynamic changes in an array of defense-related volatile and nonvolatile secondary metabolites. A scaled response relative to herbivory levels and nutrient availability would be adaptive, particularly under nutrient-limited conditions, in minimizing the costs of expressed defensive pathways and synthesis. In this study, we investigated effects of varying nitrogen (N) fertilization (42, 112, 196, and 280 ppm N) on levels of cotton plant (Gossypium hirsutum) phytohormones [jasmonic acid (JA) and salicylic acid (SA)], terpenoid aldehydes (hemigossypolone, heliocides H1, H2, H3, and H4), and volatile production in response to beet armyworm (Spodoptera exigua) herbivory. Additional bioassays assessed parasitoid (Cotesia marginiventris) host-searching success in response to cotton plants grown under various N fertilizer regimes. At low N input (42 ppm N), herbivore damage resulted in significant increases in local leaf tissue concentrations of JA and volatiles and in systemic accumulation of terpenoid aldehydes. However, increased N fertilization of cotton plants suppressed S. exigua-induced plant hormones and led to reduced production of various terpenoid aldehydes in damaged mature leaves and undamaged young leaves. While increased N fertilization significantly diminished herbivore-induced leaf volatile concentrations, the parasitism of S. exigua larvae by the parasitoid C. marginiventris in field cages did not differ among N treatments. This suggests that, despite significant N fertilization effects on herbivore-induced plant defenses, at short range, the parasitoids were unable to differentiate between S. exigua larvae feeding on physiologically different cotton plants that share large constitutive volatile pools releasable when damaged by herbivores. |
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Keywords: | Plant– herbivore interactions Tritrophic interactions Plant resistance Direct defense Indirect defense Spodoptera exigua Malvaceae Hymenoptera Lepidoptera Noctuidae Braconidae Cotesia marginiventris Optimal defense (OD) theory |
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