Review on Concepts in Biological Control of Plant Pathogens

Biological disease control is an attractive alternative strategy for the control of plant diseases. Meanwhile, it also provides practices compatible with the goal of a sustainable agricultural system. Understanding the mechanisms of biological control of plant diseases through the interactions between antagonists and pathogens may allow us to select and construct the more effective biocontrol agents and to manipulate the soil environment to create a conducive condition for successful biocontrol. Many factors have to be considered in deciding whether a biological system is feasible for the control of a particular pathogen. Of prime importance is the availability of a suitable antagonist capable of maintaining itself on the host plant. The environment under which the crop is grown will play a significant part in determining whether effective population levels of an antagonist can be established in competition with the existing microflora. Environment may also govern the choice of antagonist; for example, yeasts can survive on leaves more readily than non-spore-forming bacteria under adverse humidity conditions. It is essential that the primary mechanism by which antagonism is brought about should be known. A variety of biological controls are available for use, but further development and effective adoption will require a greater understanding of the complex interactions among plants, people and the environment. With people turning more health conscious Biological control seem to the best alternative to disease suppression. Bio-agents bring the disease suppression with no environmental hazards. Research has proved that the bio agents trigger the growth of plants. Bio agents themselves being non-pathogenic to plants need to be formulated in a way that favours the activity and survival of microbe it contains. Moreover, the organism that suppresses the pathogen is referred to as the biological control agent (BCA). More broadly, the term biological control also has been applied to the use of the natural products extracted or fermented from various sources. These formulations may be very simple mixtures of natural ingredients with specific activities or complex mixtures with multiple effects on the host as well as the target pest or pathogen. And, while such inputs may mimic the activities of living organisms, non-living inputs should more properly be referred to as biopesticides or biofertilizers, depending on the primary benefit provided to the host plant. Over the past few years, the novel applications of molecular techniques have broadened our insight into the basis of biological control of plant diseases. New molecular approaches have been available for assessment of interaction between the antagonist and pathogen, ecological traits of antagonists in rhizosphere and improving the efficacy of bacterial, fungal and viral biocontrol agent. Currently, biological control will thus be an alternative strategy for the control of plant diseases given the history of fungicides in the near future. However, other methods in IPM for crop disease control are still necessary in various environmental conditions, because an agro-ecosystem is a variable and functioning system that includes several factors that influence disease and crop development. Consequently, for economic threshold, other control strategies of IPM besides biological control should be also considered and applied to effectively reduce the disease development and the yield loss of crops in the different crop systems. Keywords: Biocontrol, biofumigation, microbial antagonism, natural compounds, pathogen.