Potential of Microbial Antagonists as Biocontrol Agents against Plant Fungal Pathogens

A variety of fungi are known to cause important plant diseases, resulting in a significant lost in agricultural crops. The plant diseases need to be controlled to maintain the level of yield both quantitatively and qualitatively. Farmers often rely heavily on the use of synthetic fungicides to control the plant diseases. However, the environmental problems caused by excessive use and misuse of synthetic fungicide have led to considerable changes in people’s attitudes towards the use of synthetic pesticides in agriculture. Today, there is an increase in the awareness of the people about the healthy food and healthy environment. In response to this need, some researchers have focused their effort to develop alternative measures to synthetic chemicals for controlling plant diseases. Among these, is that referred to as biological control using microbial antagonists. Many microbial antagonists have been reported to posses antagonistic activities against plant fungal pathogens, such as Pseudomonas fluorescens, Agrobacterium radiobacter, Bacillus subtilis, B. cereus, B. amyloliquefaciens, Trichoderma virens, Burkholderia cepacia, Saccharomyces sp, Gliocadium sp. Three species of rhizobacteria isolated from rhizospheres of rice grown in Bali, i.e. Enterobacter agglomerans, Seratia liquefaciens and Xanthomonas luminescens were found to effectively suppressed the growth of Pyricularia oryzae Cav. the cause of rice blast disease. Understanding the mechanism by which the biocontrol of plant diseases occurs is critical to the eventual improvement and wider use of biocontrol method. These mechanisms are generally classified as competition, parasitism, antibiosis, and induction of host resistance. Over the past forty years, research has lead to the development of a small commercial sector that produces a number of biocontrol products. The market share of biopesticides of the total pesticide market is less than three percent. However, significant expansion is expected over the next decades due to the expanded demand for organic food, and increased demand for safer pesticides in agriculture and forestry. The challenge is to develop a formulation and application method that can be implemented on a commercial scale, that must be effective, reliable, consistent, economically feasible, and with a wider spectrum. Continual laboratory works followed by field experiments are needed to establish excellent biocontrol agents particularly against plant fungal pathogens.