RESUMO
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 et al. 2018). During grinding using mortar and pestle, 5 mL water was added (Islam et al. 2023) after which the suspension (20 µL) was then streaked onto the selective medium (S-PG) (Tsushima et al. 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 et al. 2009), and glu-FW (5'-GAAGTGTCGCCGATGGAG-3') and glu-RV (5'-CCTTCACCGACAGCACGCAT-3') primers (Maeda et al. 2006). The PCR products were visualized on 1% agarose gel resulting amplicons of 1494bp for 16S-rDNA and 529bp for gyrB. The PCR results revealed 529bp amplification for gyrB 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 Burkholderia glumae. 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 gyrB were deposited in Genbank (OR573691 and PP332812 respectively). The homology of 16S rDNA resulted over 98% with B. glumae (OK559611 and ON870618.1) and 100% with B. glumae (PP332812 and KX213523) for gyrB gene. To confirm B. glumae 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 et al. 2009). Typical BPB like symptoms were observed after 3 weeks post inoculation. The pathogen was again confirmed by reisolating from the infected spots as B. glumae to fulfill Koch's postulates. This report confirms the presence of B. glumae 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.
RESUMO
The application of Trichoderma is a form of biological control that has been effective in combating Xanthomonas oryzae pv. oryzae, the causative agent of the devastating disease known as bacterial blight of rice. In this present study, four strains of Trichoderma, viz., T. paraviridescens (BDISOF67), T. erinaceum (BDISOF91), T. asperellum (BDISOF08), and T. asperellum (BDISOF09), were collected from the rice rhizosphere and used to test their potentiality in reducing bacterial blight. The expression patterns of several core defense-related enzymes and genes related to SA and JA pathways were studied to explore the mechanism of induced resistance by those Trichoderma strains. The results primarily indicated that all Trichoderma were significantly efficient in reducing the lesion length of the leaf over rice check variety (IR24) through enhancing the expression of core defense-related enzymes, such as PAL, PPO, CAT, and POD activities by 4.27, 1.77, 3.53, and 1.57-fold, respectively, over control. Moreover, the results of qRT-PCR exhibited an upregulation of genes OsPR1, OsPR10, OsWRKY45, OsWRKY62, OsWRKY71, OsHI-LOX, and OsACS2 after 24 h of inoculation with all tested Trichoderma strains. However, in the case of RT-PCR, no major changes in OsPR1 and OsPR10 expression were observed in plants treated with different Trichoderma strains during different courses of time. Collectively, Trichoderma induced resistance in rice against X. oryzae pv. oryzae by triggering these core defense-related enzymes and genes associated with SA and JA pathways.