Role of Bradyrhizobium sp. SEMIA6144 Nod factors in the protection of peanut plants against the phytopathogen S. rolfsii

FIGUEREDO, MARÍA SOLEDAD; IBAÑEZ, FERNANDO; FABRA, ADRIANA

Córdoba

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 in the establishment of the rhizobia?legume association is a highly specific exchange of signal molecules. Plant roots exude signal molecules, mainly flavonoids, which induce bacterial nod gene expression, resulting in synthesis of bacteria-to-plant signal molecules, called Nod factors. It is interesting to note that the signaling occurring at the beginning of the N2 fixation symbiosis involves exchange of flavonoides and chitin based compounds because the plants have a well-characterized ability to detect chitin fragments, elicitors of plant defense reaction and constituents of fungal cell walls, and, in response, to produce phytoalexins, often flavonoides. Previous studies in our laboratory demonstrated that the peanut symbiont Bradyrhizobium sp. SEMIA6144 protect peanut plants against S. rolfsii through a mechanism that seems to involve the plant?s systemic defense response (Figueredo y col., 2014). The aim of this study was to evaluate whether the Bradyrhizobium sp. SEMIA6144 Nod factors are involved in the protection of peanut plants against S. rolfsii.In order to grow plants, we used a system consisting of two pots with sterile vermiculate 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 the communicating hole. Two days after planting, the radicle was inoculated with the bacterial strains Bradyrhizobium sp SEMIA6144 or an isogenic Bradyrhizobium sp. strain (V2) unable to synthesize Nod factors (Ibáñez and Fabra 2011). A week later, the plants were challenged with the pathogen putting a wheat seed infested with S. rolfsii mycelia. At 30 days post-pathogen challenge, disease symptoms were recorded and plants were harvested to determine their shoot and root dry weights. At 30 days post-pathogen challenge, the disease incidence was higher in plant inoculated with the mutant strain than in plants inoculated with Bradyrhizobium sp. SEMIA6144, 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 concluded that the rhizobial Nod factors contribute to the protection of peanut plants against S. rolfsii by the microsmbiont Bradyrhizobium sp. SEMIA6144.Supported by CONICET, SECYT-UNRC, ANPCyT