SELECTION OF BIOLOGICAL-CONTROL AGENTS FOR CONTROLLING SOIL AND SEED-BORNE DISEASES IN THE FIELD

Different screening methods for selection of biological control agents (BCAs), for controlling soil and seed-borne diseases, are discussed. The shortcomings of laboratory methods focused on mechanism of action are discussed and we conclude that these methods should be used with c aution if candidates with multifactorial or plant mediated mechanisms of control are to be obtained. In vitro screens may be useful for spec ific groups of microorganisms, thus, screens for antibiotics may be re levant for Streptomyces spp., and promising results have been obtained using soil plating or precolonized agar methods to screen for mycopar asitism and competitive saprophytic ability. Experience with screening in the Nordic programme 'Biological control of seed borne diseases in cereals' is summarized. Research in the four participating countries- Finland, Sweden, Norway and Denmark-followed the same paradigm: that o f obtaining antagonists, well adapted to different Nordic environments , and developing them as effective BCAs. Potential antagonists were is olated from different sources and in planta screening methods were dev eloped in order to optimize selection of antagonists effective against a range of seed borne pathogens. Screens in the laboratory or greenho use were followed by screening in the field. The different screening p rocedures are compared and evaluated.