Bacillus-Mediated Oxidative Burst Enhances Resistance against Sheath Rot Disease in Rice
Shraddha Bhaskar Sawant
Department of Plant Pathology, Bihar Agricultural University, Sabour, Bhagalpur, 813210 Bihar, India.
Repudi Shalem Raju *
Regional Agricultural Research Station, PoA, ANGRAU, Maruteru, Andhra Pradesh 534122, India.
S. R. Prabhukarthikeyan *
ICAR-National Research Centre for Banana (NRCB), Tiruchirappalli, 620 102, Tamil Nadu, India.
T.Srinivas
Regional Agricultural Research Station, PoA, ANGRAU, Maruteru, Andhra Pradesh 534122, India.
Y. Suneetha
Regional Agricultural Research Station, PoA, ANGRAU, Maruteru, Andhra Pradesh 534122, India.
*Author to whom correspondence should be addressed.
Abstract
Aim: This study aimed to understand the Bacillus-mediated resistance against the sheath rot pathogen (Sarocladium oryzae) in rice, specifically focusing on the generation of reactive oxygen species (ROS), such as superoxide (O₂⁻) and hydrogen peroxide (H₂O₂), as an early defense response in rice sheaths treated with Bacillus bioformulations and subsequently challenged with S. oryzae.
Study Design: An experimental design involving various Bacillus bioformulations (liquid and talc) applied as seed treatment, seedling dip, and foliar spray, followed by challenge inoculation with Sarocladium oryzae.
Place and Duration of Study: The study was conducted as part of the research on Bacillus-mediated resistance in rice at ICAR-NRRI, Cuttack during 2021-2022.
Methodology: Rice leaf sheaths were sampled at 0, 24, 48, 72, 96, 120, and 144 hours after pathogen inoculation. Treatments included liquid and talc formulations of Bacillus isolates (RBS-57, BS-5, RBS-3). Histochemical assays using nitro blue tetrazolium (NBT) for O₂⁻ and diaminobenzidine (DAB) for H₂O₂ were employed to detect and localize these reactive oxygen species.
Results: Histochemical assays revealed an early and enhanced accumulation of both O₂⁻ and H₂O₂ in Bacillus-treated plants. The RBS-57 liquid formulation showed the highest O₂⁻ and H₂O₂ activities, peaking at 72 hours post-inoculation, which was significantly earlier and more intense than in control plants. This rapid and synchronized oxidative burst suggests an effective priming of host defense responses. H₂O₂ accumulation was confirmed by DAB staining, appearing as dark brown spots, and was observed exclusively in inoculated leaves, indicating a localized and pathogen-induced response. Similarly, O₂⁻ accumulation, visualized as intense blue spots with NBT solution, was higher in RBS-57 liquid bioformulation treatment, peaking at 72 hours, and was also localized to inoculated leaves. Chemical treatments resulted in significantly lower O₂⁻ activity compared to Bacillus treatments.
Conclusion: The findings confirm the pivotal role of Bacillus-mediated ROS signaling in restricting Sarocladium oryzae infection in rice. The ability of Bacillus bioformulations to induce a rapid and intense oxidative burst positions them as valuable tools in developing sustainable and eco-friendly strategies for managing sheath rot disease, thereby contributing to global food security. In nutshell, this study highlights bacillus-based bioformulations as an eco-friendly and sustainable strategy for effective sheath rot disease management in rice.
Keywords: Sheath rot, Sarocladium oryzae, plant growth-promoting rhizobacteria, Bacillus bioformulations, reactive oxygen species, induced systemic resistance