Introduction

Why biological control?

The past 15 years have witnessed a dramatic increase in research related to biological control. The current perception that biocontrol will have an important role in commercial agriculture in the future contrasts markedly with previously-held views that biocontrol agents perform too inconsistently, or are too narrow in their spectrum of activity, as compared with chemical pesticides, to be commercially feasible on a large scale. Renewed interest in biological control is in part a response to widespread concern about the potential negative impact of chemical pesticides on public health and the environment. Furthermore, the techniques of molecular biology have revolutionized the field by facilitating the identification of the molecular basis of pathogen suppression and by providing the means for construction of ‘superior’ biocontrol agents. New biocontrol agents resulting from recent intensive research are slowly becoming available to agriculture, and the trend should accelerate throughout this decade. One example is Gliocladium virens, which is being marketed in potting-mix to control Pythium and Rhizoctonia (see Lumsden and Walter, Chapter 25).

This chapter deals with the potential benefits and risks from the introduction of biocontrol agents for the control of root diseases of wheat, as well as the impediments to the application of this technology in commercial agriculture. The focus of the chapter is on biological control of take-all of wheat by fluorescent Pseudomonas spp. because it is a model system for the study of the molecular basis of pathogen suppression, root colonization by introduced bacteria and field application of biocontrol agents.