Abstract
Plant growth promoting rhizobacteria (PGPR) are found to control the plant diseases by adopting various mechanisms. Induced systemic resistance (ISR) is an important defensive strategy manifested by plants against numerous pathogens especially infecting at aerial parts. Rhizobacteria elicit ISR by inducing different pathways in plants through production of various metabolites. In the present study, potential of Bacillus spp. KFP-5, KFP-7, KFP-17 was assessed to induce antioxidant enzymes against Pyricularia oryzae infection in rice. The antagonistic Bacillus spp. significantly induced antioxidant defense enzymes i-e superoxide dismutase (1.7–1.9-fold), peroxidase (3.5–4.1-fold), polyphenol oxidase (3.0–3.8-fold), phenylalanine ammonia-lyase (3.9–4.4-fold), in rice leaves and roots under hydroponic and soil conditions respectively. Furthermore, the antagonistic Bacillus spp significantly colonized the rice plants (2.0E+00–9.1E+08) and secreted multiple biocontrol determinants like protease (1.1–5.5 U/mg of soil or U/mL of hydroponic solution), glucanase, (1.0–1.3 U/mg of soil or U/mL of hydroponic solution), siderophores (6.5–42.8 μg/mL or mg) in the rhizosphere of different rice varieties. The results showed that treatment with Bacillus spp. enhanced the antioxidant defense activities in infected rice, thus alleviating P. oryzae induced oxidative damage and suppressing blast disease incidence.
Highlights
Plant growth promoting rhizobacteria (PGPR) are being widely used as an alternative to chemical fungicides and fertilizers due to their eco- friendly nature [1,2,3,4]
Quantity of biocontrol determinants produced by Bacillus spp Bacillus spp. strains KFP-5, KFP-7 and KFP-17 produced variable quantities of siderophore, protease and glucanase in absence as well as presence of rice blast pathogen P.oryzae
The maximum biocontrol determinants were produced in presence of P.oryzae i-e., siderophore (29– 43.3μg/mL), protease (20.9–29.3U/mL) and glucanase (0.73–1.24 U/mL)
Summary
Plant growth promoting rhizobacteria (PGPR) are being widely used as an alternative to chemical fungicides and fertilizers due to their eco- friendly nature [1,2,3,4]. They suppress phytopathogens by utilizing various mechanisms in their habitation. ISR is an effective defensive mechanism which is manifested as a result of certain physiological changes in the plant, such as modification in cell wall structure and de novo synthesis of antimicrobial compounds like pathogenesis-related (PR) proteins and phytoalexins, that prevent the dispersion of pathogens [7,8,9,10,11]. The antioxidant enzymes peroxidase (PO), phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) might be elicitors of ISR as their activity in plant has been highly correlated with disease suppression [12].
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