The potential of endopytic bacteria as plant growth promoter and biocontrol agent for bacterial leaf blight / Rashidah Abd Halim

Excessive use of synthetic agents to control bacterial leaf blight disease in rice hinders with environmental and health issues. Endophytic bacteria, which can be recovered from inside plant tissues such as roots, stems, and leaves, might overcome this limitation due to their unique ecological niche inside plant roots, where they are sheltered from external environmental disturbances. Some of these bacterial endophytes have beneficial effects on their host plants and stimulate plant growth or reduce disease symptoms, apparently through mechanisms that are similar to those proposed for plant growth promoting rhizobacteria (PGPR). The objective of this study was to assess a collection of endophytic bacteria from the roots and leaves of rice plants and explore the potential used to control bacterial leaf blight and plant growth promoting (PGP) traits. Two hundred and twelve isolates were obtained from the roots and leaves of rice samples collected from different rice cultivation fields across Peninsular Malaysia. Morphological and biochemical analysis grouped these isolates into 6 distinct groups. Further, 16S rRNA gene sequencing analysis identified these isolates as Bacillus cereus strain DQ884352.1, Bacillus subtilis strain KF957733, Geobacillus thermoparaffinivorans strain KP218042.1, Pseudomonas fluorescens strain MH620728.1, Enterobacter sp. strain CP028975, and Gamma proteobacterium strain CP032508.1. All of these isolates exhibited various abilities to produce growth regulators that contributed to solubilizing phosphate, produced indole-3-acetic acid (IAA), synthesised siderophores, were able to fix nitrogen, and showed antagonistic activities against Xanthomonas oryzae pv. oryzae, pathogenic bacteria under in vitro conditions. All the six endophyte isolates were further evaluated for their ability to enhance plant growth and disease suppression efficiency under greenhouse conditions. Results revealed that Geobacillus thermoparaffinivorans strain KP218042.1 significantly (p < 0.05) enhanced the root length (29.73 ± 1.55 cm) and showed a significantly (p < 0.05) maximum grain yield (34.23 ± 7.79). Disease treatment experiments showed that the suppression efficiency of Geobacillus thermoparaffinivorans strain KP218042.1 treatments was 83.49 %, which was significantly higher (p < 0.05) than that of the bactericide treatment (24 %). These results suggest that Geobacillus thermoparaffinivorans strain KP218042.1 may be useful as biofertilizers and/or biocontrol agents in sustainable agricultural practices.