SA, ABA and Pseudomonas fluorescens elicit defense responses in tomato against Alternaria blight

Alternaria blight causes significant losses in tomato. High disease severity during fruiting stage restricts the applicability of chemicals. Chemical pesticides can be substituted by resistance inducing agents. In present investigation, two resistance inducing agents namely Salicylic acid and Abscisic acid and a plant growth promoting rhizobacteria Pseudomonas fluorescens strain PBAT-2 (Psf) were used to assess their effect on Alternaria blight disease severity through the activity of defense-related compounds i.e. Peroxidase (POD), Polyphenol oxidase (PPO), Phenyl ammonia lyase (PAL), total phenolic content along with pathogenesis-related gene PR-1 and beta-1,3-glucanase (GLU) gene expression in tomato. SA, ABA and Psf reduced disease severity significantly as compared to control. A significant increase in the activity of POD, PPO, PAL and total phenol content was recorded in all the three treatments over control. POD, PPO, PAL levels were significantly high at 24 h and 48 h post Alternaria solani inoculation, whereas total phenolic content increased up to 72 h. The expression of PR-1 and GLU gene was upregulated at 24 h post A. solani inoculation in SA and ABA treated leaves. However, these genes were unexpressed in Psf treated plants which confirms the role of SA and ABA in systemic acquired resistance. These findings suggest that SA, ABA and Psf can be used in early blight management in tomato without affecting the quality of the fruit.