Genetic Manipulation for Improvement of Microbial Biocontrol Agents

Abstract

During the last few years genetic modification of microorganisms to improve their biological control of plant pathogens has created some very interesting results, which indicates that molecular biology can be used not only to understand the mechanism behind biological control, but also to improve biocontrol ability. It is, however, important to remember that in most strains, the ability to control disease will be explained by more than one mechanism, and the host for genetic modification has to be ecologically fit in the environment where the biocontrol is to be performed. Modification of a biocontrol mechanism may result in an improved biocontrol ability, but may also give unexpected effects. The effect of a new or modified biocontrol agent must therefore be carefully determined empirically for each host-pathogen system. There is also in the public a resistance against introduction of genetically modified organisms into the environment, which probably will slow down the introduction of genetically modified biocontrol agents in many countries. So far only a few modified organisms are on the market, e.g. the deletion mutants A. radiobacter strain K1026 (Section 25.3.3) and the Ice- mutant of P. syringae (Section 25.3.6), plus the protoplast fusant T. harvanum strain 1295-22 (Bio-Trek 22) (Section 25.2.2), but with the great demand for alternatives to chemicals in plant protection it is expected that more modified organisms soon will become commercially available.