Analysis of defence enzymes induced by antagonistic bacteriumBacillus subtilis strain AR12 towardsRalstonia solanacearum in tomato

Abstract

Bacterial wilt, caused byRalstonia solanacearum (Smith) Yabuuchiet al., is an economically important disease on tomato in many provinces of China. Antagonistic bacteriumBacillus subtilis strain AR12 was used to control bacteria wilt of tomato (Lycopersicon esculentum Miller) in the greenhouse. The biocontrol efficiency was as high as 90.18%. Superoxide anion and hydrogen peroxide generation rates and changes in phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities were studied in tomato plants. Antagonist AR12 advanced and increased significantly activities of PAL, PPO, POD and SOD. As comparison, the activities of these four enzymes increased less and later in tomato only treated withR. solanacearum TM15 (control 2), and kept lowest level with few change in tomato with sterilised water (control 1). The maximum activities of these four enzymes in tomato treated with AR12 occurred in different stages: activity of PAL, PPO, POD, and SOD increased to the top level at 48, 48, 12 and 12 h, respectively, after pathogen inoculation and kept high level for some time. H2O2 is associated with hypersensitive response (HR) during systemic acquired resistance. H2O2 content increased significantly in tomato treated with AR12, but HR response was not seen. CAT and APX are the key H2O2 detoxifying enzymes. Activities of APX in tomato treated with AR12 were increased significantly, while CAT was degraded until 80 h after pathogen inoculation. This work support the view that increased antioxidant enzyme activities could be involved at least in part, in the beneficial effects of plant growth-promoting rhizobacteria strains on the performance of vegetable grown under the pathogen infection conditions.