Dissertation Research: Evolution of Resistance, Tolerance and Species Interactions in a Brassica/Herbivore/Pathogen System

University Of California-Irvine, Irvine CA

Investigators

Abstract

Weis 0073558 The proposed research will use greenhouse and field experiments with the wild mustard Brassica rapa and three of its natural enemies to determine 1) genetic correlations between resistance to enemies, 2) genetic correlations between tolerance of enemies, 3) genetic correlations between tolerance and resistance to a particular enemy, and 4) ecological interactions between natural enemies. A greenhouse component of the research will provide the controlled conditions necessary for determination of genetic correlations, and a field component will allow for determination of the impacts of herbivores in the field. Groups of plants from half-sib families will be exposed to different treatments, each consisting of exposure to one natural enemy or a combination of natural enemies. Resistance and tolerance of each plant family to their natural enemies will be determined from treatments exposed to single enemies. Comparison of the impact of attack by multiple enemies with the impact of each of those enemies alone will determine whether there are ecological interactions. If there are interactions, then the impact of a group of natural enemies will differ from the sum of their independent impacts. This research will provide important insights into the genetic structure of plant defense against their natural enemies. Plants can cope with attack by natural enemies by either avoiding or minimizing damage by the enemies (resistance) or by regrowing after damage has occurred (tolerance). In order to understand how these interact to form an integrated defense system, two potential constraints need to be understood: 1) genetic correlations between resistance or tolerance traits and 2) ecological interactions between enemies. When resistance is genetically correlated to tolerance, then any selection program to improve the one will cause the other to decline. When enemies interact, their effects on plant performance can be synergistic, thus the value of resistance to one enemy in isolation may not predict the total value of resistance to both. Investigating these two constraints can help increase our understanding of the contribution of plant defense on herbivore diversity, and aid in the structuring of plant breeding programs for crops that face multiple harmful pests.