Co-inoculation of Bradyrhizobium sp. and Bacillus sp. on peanut: effect on their plant growth-promoting activities

FIGUEREDO, MARÍA SOLEDAD; TONELLI, MERÍA LAURA; IBAÑEZ, FERNANDO; FABRA, ADRIANA

Londrina

Congreso; XXVII RELAR; 2016

The combined inoculation of bacteria able to promote plant growth by different mechanisms constitutes an alternative or complement to the use of agrochemicals. Previous studies in our laboratory demonstrated that the native strain Bacillus sp. CHEP5 induces systemic resistance (ISR) on peanut plants protecting against the phytopathogen Sclerotium rolfsii. Peanut plants also interact with Bradyrhizobium sp. SEMIA6144, establishing a nitrogen fixing symbiotic association. The aim of this work was to evaluate the effect of simultaneous inoculation of both beneficial microorganisms and the fungal pathogen on the plant responses that are triggered in the individual interaction with each of them. The plantlet?s radicles were inoculated with pure or mixed bacterial cultures and after 7 days the shoots were challenged with S. rolfsii. At 40 days post-bacterial inoculation, disease incidence (DI) was recorded and plants were harvested to determine nodule number (NN) and their dry weight (NDW), total chlorophyll content (TCC) and shoot (SDW) and root (RDW) dry weight. In plants inoculated with both bacteria, in absence of the pathogen, the NN formed didn?t differ from that of plants inoculated only with the rhizobial strain. Furthermore, the NDW and SDW of plants co-inoculated were significantly higher than control plants inoculated only with SEMIA6144. These results suggest that CHEP5 positively affects SEMIA6144 symbiotic phenotype. As it was expected, in plants inoculated with SEMIA6144 and challenged with the phytopathogen, NN y NDW decreased drastically. However, when plants were inoculated with both bacteria (SEMIA 6144 and CHEP5) these parameters increased significantly. These results indicate that CHEP5 contributes to a partial reversion of the phytopathogen harmful effects. On the other hand, DI, TCC, SDW and RDW of plants co-inoculated didn?t differ from those of plants inoculated only with CHEP5, suggesting that SEMIA6144 doesn?t affect the capacity of CHEP5 to induce systemic resistance against S. rolfsii. Moreover, in plants inoculated only with SEMIA6144 the DI was lower and the TCC, SDW and RDW were higher than plants treated only with S. rolfsii, suggesting that SEMIA6144 is also able to protect peanut plants against phytopathogen through ISR. Plants inoculated with a SEMIA6144 derivative mutant (V2) unable to produce Nod factors showed higher DI than plants inoculated with wild type strain. These results suggest that Nod factors are required for ISR induced by SEMIA6144, contributing to protect peanut plants against S. rolfsii. This work was supported by SECyT-UNRC, CONICET, ANPCyT