Multitrophic effects of plant resistance: from basic ecology to application in transgenic crops

Research output: Thesisinternal PhD, WU

Abstract

Plants have evolved a wide array of direct and indirect resistance traits that prevent or reduce herbivory by insects. The aim of this thesis was to study the effects of direct and indirect plant resistance traits on the multitrophic interactions between brassicaceous plants, leaf-chewing and phloem-sucking aboveground herbivores and their natural enemies, parasitoids and predators. Brassica oleracea cultivars and Arabidopsis thaliana ecotypes were used that differ in production of glucosinolates or emission of volatiles, secondary plant chemicals acting in direct and indirect resistance respectively. There was a considerable intraspecific variation in the multitrophic effects of plant resistance traits in both plant species. In the field, bottom-up forces (plant chemistry and morphology) appeared more important for herbivore abundance than plant-mediated top-down forces (attraction and arrestment of natural enemies). Under greenhouse conditions, glucosinolates affected the performance of herbivores and that of their natural enemies. The performance of both a generalist and a specialist caterpillar was negatively correlated with glucosinolates in the plant, whereas that of a parasitoid of the specialist caterpillar was positively correlated with glucosinolates. Performance of a specialist aphid was positively correlated with phloem glucosinolates, and the aphid selectively sequestered these glucosinolates. Glucosinolates and their volatile hydrolytic products correlated negatively with the performance and behaviour of one of the predators of this aphid, but positively with that of one of its parasitoids. These results suggest that direct and indirect resistance traits can be in conflict, but they can also work in concert to enhance resistance to herbivores, depending on the biology of the herbivore and carnivore involved. Transgenic A. thaliana plants engineered to emit larger amounts of volatile terpenoids repelled the aphid, attracted the parasitoid, but did not affect predator behaviour.

These fundamental ecological results provided the background information required to strengthen ecological risk analysis for transgenicplants in the framework of the programme ‘Ecology Regarding Genetically modified Organisms’ funded by the Dutch government. The effects of transgenic plants on non-target organisms were compared with the baseline variation in the effects on non-target organisms that exists among conventional varieties or, in the case of A. thaliana, wild ecotypes. Four B. oleracea cultivars and three A. thaliana ecotypes were selected to represent the baseline variation. The baseline variation in effects on target and non-target organisms was relatively consistent over different environments, soil types and time. The effects of transgenic A. thaliana plants altered in direct and indirect resistance on non-target organisms were mostly within the baseline variation in these effects. Finally, the knowledge gained was applied to develop guidelines for governmental regulators that can be used to assess the potential ecological effects of transgenic crops on non-target organisms, in relation to baseline variation.

 

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Dicke, Marcel, Promotor
  • Vet, Louise, Promotor
  • van Loon, Joop, Co-promotor
Award date16 Mar 2012
Place of PublicationS.l.
Print ISBNs9789461732064
Publication statusPublished - 2012

Keywords

  • brassicaceae
  • defence mechanisms
  • insect pests
  • multitrophic interactions
  • parasitoids
  • predators
  • glucosinolates
  • volatile compounds
  • transgenic plants
  • nontarget organisms
  • ecological risk assessment

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