Molecular techniques for the study of rhizobial ecology in the field

Traditional approaches to the study of rhizobial ecology in the field have used spontaneous or induced antibiotic resistance markers, or various antigenic detection techniques including fluorescently-labelled antibodies, the ELISA technique or immunodiffusion. All these approaches suffer certain disadvantages, the key ones being the labour-intensive nature of the assays, which limits the amount of data that can be collected, and the lack of sufficient specificity to allow unambiguous strain identification. New techniques that are based on molecular biology can provide significant advantages. Introduced marker genes, such as the β-glucuronidase (gusA) gene allow the analysis of all the nodules on a single root system with a simple colour assay, thereby dramatically increasing data throughput. Nucleic-acid-based techniques, which identify strains from characteristic DNA or RNA sequences or profiles, provide an excellent tool for strain verification and for surveying population structure.