First Report of Bacterial Panicle Blight of Rice Caused by Burkholderia glumae in Southern China

Abstract

Rice (Oryza sativa L.) is the staple food for people in southern China. Bacterial panicle blight of rice (BPBR) caused by Burkholderia glumae, known as grain blight or seedling rot, leads to rice yield losses up to 75% and threatens rice production (Nandakumar et al. 2009). In 2007, B. glumae was isolated from symptomless rice seeds in Hainan, China (Luo et al. 2007). In 2017, 43 panicle samples showing typical symptoms of BPBR with reddish-brown, aborted or partially filled grains and linear lesions on flag-leaf sheaths were collected for bacterial isolation from fields in 15 towns of Guangxi and Guangdong provinces, China (cvs. Longfengyou139, Benyou9901, Baixiangyou 9978, Yaliangyou, Quanyousimiao, etc.). The diseased panicle incidence was about 6.5 to 20% in the field. The infected grains were sterilized with 70% ethanol for 30 to 60 s, rinsed with distilled water three times, cut and crushed, and soaked in 1 ml of distilled water for 10 min (Mirghasempour et al. 2018). The suspension was streaked and cultured on nutrient agar (NA) medium containing ampicillin (50 µg/ml) for 16 to 24 h at 37°C. The circular, smooth-margined, convex colonies were selected for further purification with serial dilution and subculturing on NA medium. The 29 isolated strains can all produce the diffusible yellow pigment on King’s B medium. Two isolated strains, GX1 and GX28, from Guangxi province were selected for the following molecular and pathogenicity assays. For molecular identification, B. glumae-specific polymerase chain reaction was first carried out using gyrase gene (GenBank D87080) primers BGgyrF (5′-GCAGCGGCAAGGAAGACG-3′) and BGgyrR (5′-GTCGTCGCCCGACGTCTC-3′). The amplified 317-bp fragments were sequenced (GenBank MN417293), and the sequence identity is up to 100% with other reported B. glumae strains 336gr-1 (GenBank assembly accession GCA_000503955), BGR1 (GenBank assembly accession GCA_000022645), and LMG2196 (GenBank assembly accession GCA_000300755) by NCBI BLASTn analysis. To further verify B. glumae, the 16S rRNA gene was also amplified with common 16s rRNA primers (5′-AGAGTTTGATCATGGCTCAG-3′ and 5′-AAGGAGGTGATCCAGCCGC-3′). Results showed that 1,525-bp 16S rRNA gene sequences from isolate GX1 (GenBank MN400210) and GX28 (GenBank MN400211) shared 99% sequence similarity with 336gr-1, BGR1, and LMG2196. For the pathogenicity test, bacterial suspension at 10⁸ CFU/ml was injected into the panicle bud at the early booting stage of rice (cvs. Zhongjiazao17, Zhongzao39, Tianyouhuazhan, and Yongyou12). The injected tissue showed the linear lesion at 2 to 3 days after inoculation; 20 to 30 days later, grains were reddish-brown, aborted and partially filled, with similar symptoms to those samples collected from rice fields of Guangxi and Guangdong provinces. The same B. glumae was reisolated from the inoculated rice plants, fulfilling Koch’s postulates. This is the first report of BPBR caused by B. glumae in southern China. The occurrence, spread, and damage of BPBR caused by B. glumae in China need to be determined for disease control in the future.