Role of Bradyrhizobium sp. SEMIA 6144 Nod factors in the protection of peanut plants against the phytopathogen Sclerotium rolfsii.

MARÍA SOLEDAD FIGUEREDO; FERNANDO IBAÑEZ; ADRIANA FABRA

Congreso; XI Congreso Argentino de Microbiología General (SAMIGE); 2015

Plants possess highly sensitive perception systems by which microbial signal molecules are recognized. The earliest event inthe establishment of the rhizobia?legume association is a highly specific exchange of signal molecules. Plant roots exude signalmolecules, mainly flavonoids, which induce bacterial nod gene expression, resulting in synthesis of bacteria-to-plant signalmolecules, called Nod factors. It is interesting to note that the signaling occurring at the beginning of the N fixation symbiosisinvolves exchange of flavonoides and chitin based compounds because the plants have a well-characterized ability to detectchitin fragments, elicitors of plant defense reaction and constituents of fungal cell walls, and, in response, to producephytoalexins, often flavonoides. Previous studies in our laboratory demonstrated that the peanut symbiont Bradyrhizobium sp.SEMIA 6144 protect peanut plants against Sclerotium rolfsii through a mechanism that seems to involve the plant?s systemicdefense response. The aim of this study was to evaluate whether the Bradyrhizobium sp. SEMIA 6144 Nod factors are involvedin the protection of peanut plants against S. rolfsii. In order to grow plants, we used a system consisting of two pots with sterilevermiculate put one above the other and connected by a hole made in the base of the upper pots. In this container,pregerminated seed peanut was placed so that its radicle was introduced into the lower pot (larger diameter) through thecommunicating hole. Two days after planting, the radicle was inoculated with the bacterial strains Bradyrhizobium spSEMIA6144 or an isogenic Bradyrhizobium sp strain (V2) unable to synthesize Nod factors (Ibáñez and Fabra 2011). A weeklater, the plants were challenged with the pathogen putting a wheat seed infested with S. rolfsii mycelia. At 30 dayspost-pathogen challenge, disease symptoms were recorded and plants were harvested to determine their shoot and root dryweights. At 30 days post-pathogen challenge, the disease incidence was higher in plant inoculated with the mutant strain than inplants inoculated with Bradyrhizobium sp. SEMIA 6144, although it was lower than those that were only pathogen challenged.Furthermore, the shoot and root dry weights were in agreement with this result. Considering the results obtained, we concludedthat the rhizobial Nod factors contribute to the protection of peanut plants against S. rolfsii by the microsmbiont Bradyrhizobiumsp. SEMIA 6144.