Molecular Diagnosis and Application of DNA Markers in the Management of Fungal and Bacterial Plant Diseases

Successful management of plant diseases is mainly dependent on the accurate and efficient detection of plant pathogens, amount of genetic and pathogenic variability present in a pathogen population, development of disease resistant cultivars and deployment of effective resistance genes in different epidemiological regions. Beside conventional methods of pathogen detection and breeding resistant cultivars, recent developments in molecular biology techniques particularly the advent of various DNA markers have greatly influenced the plant protection methods. Pathogen detection has relied on isolation of microorganisms and observations of symptoms they induce on susceptible hosts. In many situations cultural, morphological and chemical markers have been used to study variation in pathogen populations. Such markers are limited, often unstable and are influenced by environmental conditions. Molecular detection of plant pathogens and characterization of genetic variability by using different DNA markers have offered additional tools in the hands of plant pathologists and plant breeders. Various PCR based and hybridization based DNA marker techniques can be used for the characterization of genetic variability in pathogens and molecular tagging of disease resistance genes. DNA markers linked to specific resistance gene can be used in marker-assisted-selection for resistance breeding, gene pyramiding and map-based cloning of the resistance genes. In this communication various uses of DNA markers in pathogen diagnostics and mapping, pyramiding and map-based cloning of disease resistance genes have been discussed.