Abstract
The usage of plant growth-promoting (PGP) Streptomyces to improve plant growth is an alternative to existing strategies of chemical fertilizers that commonly caused environmental pollution. The aim of this study was to isolate and characterize PGP Streptomyces from Malaysian rice fields with antagonistic activity against Bacterial Panicle Blight disease in rice caused by Burkholderia glumae. A total of 50 bacterial isolates were recovered from the soil, rhizosphere, and endosphere; 22% showed antagonistic activity against B. glumae. Molecular identification using 16S rRNA amplification and phylogenetic tree analyses revealed that the antagonistic isolates belonged to the genus Streptomyces. Among the antagonistic isolates, Streptomyces sp. TBS5 (26.35 ± 0.14 mm) demonstrated the most antagonistic activity (p < 0.05) against B. glumae. Through API® ZYM analysis, the antagonistic isolates were revealed to have phosphoric hydrolase, ester hydrolase, peptide hydrolase, and glycosidase activities that play a crucial role in plant growth promotion. The antagonistic isolates demonstrated the highest (80%) PGP traits including able to fix nitrogen and solubilize phosphate, as well as produce siderophore and indole-3-acetic acid. Plant growth promotion assay under laboratory and greenhouse conditions were analyzed with the treatment of rice, Oryza sativa, seeds with the antagonistic isolates. Seeds treated with Streptomyces sp. TBS5, JAS2, R2-7, and TKR8 showed improvement in vigor index by more than 100% compared to water-treated control plants under both conditions. Augmentation of root length showed an overall increment of more than 101.5% under laboratory condition and 151.9% under greenhouse condition using Streptomyces sp. TBS5, JAS2, R2-7, and TKR8 treatments. Results suggest that Streptomyces sp. TBS5, JAS2, R2-7, and TKR8 are a good candidate to be developed as both biocontrol agent against B. glumae and PGP agent in rice.
Highlights
Bacterial Panicle Blight (BPB) is a severe seed-borne bacterial disease of rice
It is noteworthy that Burkhoderia gladioli infection produced similar symptoms as B. glumae; suggesting that BPB can be caused by B. gladioli [12]
Malaysian rice fields as a potential biocontrol agent against B. glumae. These analyses facilitated the best selection of plant growth-promoting (PGP) Streptomyces candidates
Summary
Bacterial Panicle Blight (BPB) is a severe seed-borne bacterial disease of rice. It was first reported in the 1950s in Japan. BPB has been widely spotted in rice-growing countries, including Asia [3,4], South and Central America [5,6,7], and Africa [8]. Rice plants infected by B. glumae show several disease symptoms which include seedling rot, panicle blighting, and leaf-sheath browning [11]. It is noteworthy that Burkhoderia gladioli infection produced similar symptoms as B. glumae; suggesting that BPB can be caused by B. gladioli [12]
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