Novel, simple and inexpensive programmed lab experiments to evaluate the biocontrol activity of rhizobacteria on fungal phytopathogens

Despite the growing importance of agricultural microbiology at the applied, productive and ecological levels, undergraduate degrees in Agronomy generally do not feature much microbiological experimentation. To address this deficiency, we have designed an experimental programme that evaluates the potential of plant growth-promoting rhizobacteria (PGPR) for the biocontrol of fungal pathogens. The approach involves an experimental laboratory class in which Agronomy students evaluate the ability of a rhizospheric Burkholderia sp. strain to inhibit the development of Sclerotium rolfsii (the causal agent of 'white wilt' disease in peanut plants). The assays cover three aspects: biochemical mechanisms associated to biocontrol properties in the bacterium, bacterium–fungus interaction (plate inhibition assays), and plant-bacterium-fungus interaction (disease control assays). Students verify the bacterial strain's ability to produce fungi-degrading enzymes, inhibit fungal growth, and protect the plant by inhibiting disease development. The assays serve as an integrative basis on which to discuss relationships between plants, bacteria, and fungi in connection with a disease which affects important regional crops. This set of experiments should help students to develop different skills which will be key in their future professional career, such as handling and designing experimental assays; comparing, discussing and solving practical problems; and drawing conclusions from their observations and the results obtained.