Assessment of Variability in Bacterial and Phytoplasmal Pathogens

Abstract

Variability is the essential requirement of bacterial and phytoplasmal pathogens inducing diseases in plants/crops to survive and perpetuate in various environmental conditions and the agricultural practices followed in different ecosystems. Variations in the genetic constitution of bacteria are reflected in their phenotypic characteristics expressed in cultural, biochemical/physiological and immunological characteristics that may have an impact on the pathogenicity (pathogenic potential) of bacterial pathogens. Growth of and production of enzymes, toxins and antibiotics by bacterial pathogens may show variations in nutrient media. Several techniques have been applied to assess the variations in the nature of enzymes and toxins elaborated by bacterial pathogens, in addition to their reactivity to antibodies. Nucleic acid-based techniques have been shown to be more efficient in differentiating strains/races of bacterial pathogens more rapidly and reliably when compared to methods based on the biological, biochemical and immunological characteristics. The phytoplasmal pathogens have not yet been successfully cultured on artificial nutrient media. Hence, differences in their cultural and biological characteristics cannot be utilized as the basis for differentiation of phytoplamas. Application of nucleic acid-based techniques have been demonstrated to be more useful and precise in differentiating the strains of phytoplasmal pathogens than the biological methods depending on the pathogenicity of these pathogens. Variations in cultural, biochemical, immunological and genetic characteristics of plant bacterial pathogens have been assessed. Phytoplasmal pathogens, on the other hand, have to be differentiated primarily based on the variations in genetic characteristics, since these pathogens are yet to be cultured on cell-free artificial media. It is important to relate the variations observed in different characteristics to the changes in the pathogen potential (virulence) of the bacterial pathogen(s) under investigation, since this information can form the basis for developing economically feasible disease management systems.