Resistance responses of rice to rice blast fungus after seed treatment with the endophytic Achromobacter xylosoxidans AUM54 strains

In the present investigation, we studied resistance imparted by seed treatment with an endophytic strain of Achromobacter xylosoxidans, AUM54, against rice blast caused by Magnaporthe oryzae. In vitro studies showed that A. xylosoxidans AUM54 was able to inhibit mycelial growth of M. oryzae by 11% and was able to increase rice germination and seedling vigor index of rice by 31 and 114%, respectively. AUM54 also showed better survivability in the spermosphere and spermoplane and was able to move systemically through the roots and stem. Among the evaluated carriers, liquid formulation amended with 2% glycerol sustained the maximum bacterial population (7.4 log cfu ml⁻¹) after six-months-storage at room temperature. Plants treated with A. xylosoxidans AUM54 followed by inoculation with M. oryzae showed a significant increase in the activities of defense related enzymes such as polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL) and chitinase. A. xylosoxidans AUM54 treatment was able to reduce blast disease incidence by 39% in treated rice plants. Additionally, inoculation with A. xylosoxidans AUM54 significantly enhanced the growth (3–13% plant height), and yield (11–31%) of inoculated rice plants under no-disease and disease conditions in the greenhouse experiments.