Towards a Unified Theory of Plant Defense

Abstract

Current theories of plant defense have arisen from several different viewpoints. Plant pathologists, being mainly interested in organisms that invade plant tissues and in problems involving exotic (unadapted) plant/pathogen interactions, have concentrated on the dynamic aspects of cellular defense (e.g., hypersensitive reactions and phytoalexins) and the genetic basis of plant resistance (e.g., the gene-for-gene hypothesis) (see Bailey and Deverall 1983). On the other hand, entomologists have been strongly influenced by the concepts of static (preformed or constitutive) plant resistance (Painter 1951). A few, however, borrowed from the pathology literature to develop concepts of dynamic (induced) defense against insect herbivores. Not surprisingly, these early workers studied insects that penetrate plant tissues and/or vector plant pathogens, e.g., aphids, (Homoptera: Aphididae) (Balch et al. 1964, Mullick 1977, Rohfritsch in this volume); siricid woodwasps, (Hymenoptera: Siricidae) (Coutts and Dolezal 1966); and scolytid bark beetles, (Coleoptera: Scolytidae) (Reid et al. 1967; Berryman 1969, 1972; Shrimpton 1978; Cook and Hain in this volume; Lieutier and Berryman in this volume). These studies provided an important bridge between pathology and entomology and drew attention to environmental influences on plant defensive capacity (i.e., predisposition). Theories emerging from these studies, however, have been functional rather than evolutionary.