Let us try to draw together some of the conclusions of the previous chapters and, what is much more difficult, try to predict where the studies will go in the next few years.

It is quite clear that there are more than enough examples of laboratory demonstrations with different diseases in different parts of the plant with different possible control agents. That is not to say that all possible control agents have been found, indeed we have hardly started looking. Even though it is possible to make a short list of the most likely organisms (Trichoderma, Pseudomonas, Bacillus, for example) that should not discourage the search for particular species or strains for the environment, plant or disease under study.

What is lacking is basic information on the environmental and genetically determined factors that control survival, colonization and effectiveness in the field. We need to know what morphological and physiological characteristics of an organism will make it successful in a particular environment. Should an organism be motile? Should it be able to exist in low nutrient conditions? Is there some special character(s) that means an organism is fitted for growth on the root, or better the root of a particular plant host? We just do not know. There is talk of using genetically engineered organisms, and we have seen examples of some of these. Maybe the molecular biologists can put in this character or take out that: such techniques are no good to us until we know what to ask for. If we could say ‘put in such and such an enzyme’ or ‘make the wall thicker or thinner or take out the polysaccharide’ then we could make a start.