Microbial enzymes in the biocontrol of plant pathogens and pests.

Despite many achievements in modern agriculture, food crop production continues to be plagued by disease-causing pathogens and pests. In many cases, chemical pesticides effectively protect plants from these pathogens. However, public concerns about harmful effects of chemical pesticides on the environment and human health have prompted a search for safer, environmentally friendly control alternatives (1–3). One promising approach is biological control that uses microorganisms capable of attacking or suppressing pathogens and pests in order to reduce disease injury. Biological control of plant pathogens offers a potential means of overcoming ecological problems induced by pesticides. It is an ecological approach based on the natural interactions of organisms with the use of one or more biological organisms to control the pathogen. Generally, biological control uses specific microorganisms that attack or interfere with specific pathogens and pests. Because of their specificity, different microbial biocontrol agents typically are needed to control different pathogens and pests, or the same ones in different environments. Agriculture benefits, and is dependent on, the resident communities of microorganisms for naturally occurring biological control, but additional benefits can be achieved by introducing specific ones when and where they are needed (4–9). Many agrochemical and biotechnological companies throughout the world are increasing their interest and investment in the biological control of plant diseases and pests. For plant pathogens alone, the current list of microbial antagonists available for use in commercial disease biocontrol includes around 40 preparations (9–11). These are all based on the practical application of seven species of bacteria (Agrobacterium radiobacter, Bacillus subtilis, Burkholderia cepacia, Pseudomonas fluorescens, Pseudomonas syringae, Streptomyces griseoviridis, Streptomyces lydicus) and more than 10 species of fungi (Ampelomyces quisqualis, Candida oleophila,Coniothyrium minitans, Fusarium oxysporum,Gliocladium virens, Phlebia gigantea, Pythium oligandrum, Trichoderma harzianum, and other Trichoderma species). The current market for biological agents is estimated at only $500 million, which is about 1% of the world’s total output for crop protection. The largest share of this market involves biopesticides marketed for insect control (mainly products based on Bacillus thuringiensis