First Report of Causing Bacterial Panicle Blight in Rice in Bangladesh.

Bacterial panicle blight (BPB) is one of the emerging diseases occurring in different Agro-Ecological Zones (AEZ) of Bangladesh and can cause up to 75% yield loss. In Bangladesh, the typical symptoms of BPB include sheath rot, panicle blight, grain spotting, and grain rot in both inbred and hybrid rice varieties, which resemble those reported by Zhou (2019). To confirm, 300 field samples of 20 panicles each with typical BPB symptoms from 20 districts (3 locations each district and 5 fields per location) were collected during mid-November 2022 for the causal pathogen(s) isolation. Nearly 70% of the panicles showed a dark brown chaffy appearance in the fields. For identification of the causal pathogen(s), 1 g of rice grains with typical BPB symptoms was surface sterilized by immersing for 15 seconds in 70% ethanol, 1 min in 3% sodium hypochlorite solution followed by rinsing the grains three times, and soaked in 1 mL sterile distilled water for 10 min (Mirghasempour . 2018). During grinding using mortar and pestle, 5 mL water was added (Islam . 2023) after which the suspension (20 μL) was then streaked onto the selective medium (S-PG) (Tsushima . 1986). Purple color colonies on the S-PG medium were selected and purified as candidate pathogens. For further confirmation, the genomic DNA of the bacterial isolates was extracted and amplified by PCR using 16SF (5'-AGAGTTTGATCCTGGCTCAG-3') and 16SR (5'-GGCTACCTTGTTACGACTT-3') (Nandakumar . 2009), and glu-FW (5'-GAAGTGTCGCCGATGGAG-3') and glu-RV (5'-CCTTCACCGACAGCACGCAT-3') primers (Maeda . 2006). The PCR products were visualized on 1% agarose gel resulting amplicons of 1494bp for 16S-rDNA and 529bp for . The PCR results revealed 529bp amplification for gene in one sample that was collected from a field in Natore (24°21'0.00" N 89°04'59.88" E) district cultivating Swarna (a local rice variety), primarily indicating the causal pathogen is . The PCR products were sequenced using both primers and sequence data was analyzed by the BLAST nucleotide program. The obtained partial sequences of 16S rDNA and were deposited in Genbank (OR573691 and PP332812 respectively). The homology of 16S rDNA resulted over 98% with . (OK559611 and ON870618.1) and 100% with . (PP332812 and KX213523) for gene. To confirm . by pathogenicity test, 10 mL (108 UFC/ml) suspension of the representative strains, 0.5 mL was then injected into the panicles and sheaths of Horidhan (a susceptible local variety) in greenhouse condition and a control was inoculated with distilled water (Nandakumar . 2009). Typical BPB like symptoms were observed after 3 weeks post inoculation. The pathogen was again confirmed by reisolating from the infected spots as . to fulfill Koch's postulates. This report confirms the presence of . causing BPB of rice in Bangladesh. Future research for the investigation of BPB and the evolutionary origins of its causal bacteria is necessary to reduce the emergence of the disease and its management in Bangladesh.