First Report of Burkholderia glumae Isolated from Symptomless Rice Seeds in China.

Burkholderia glumae causes grain rot and seedling rot of rice (Oryza sativa L.). It is seedborne and has caused severe damage in Japan (1). Since 1997, efforts have been made to detect the pathogen in rice seeds in China (2), where no typical symptoms have been observed in the rice paddy fields. Isolation from 623 symptomless rice seed samples yielded two samples, originally produced in Hainan province, with possible B. glumae (0.32%). Six bacterial strains isolated from these two samples showed characteristics similar to those of the standard reference strain of B. glumae, LMG 1837T from Belgium, in phenotypic tests including the Biolog identification system (version 4.2; Hayward, CA), pathogenicity tests, and gas chromatographic analysis of fatty acid methyl esters (FAMEs) using the Microbial identification System (MIDI Company, Newark, DE) with aerobic bacterial library (TABA50). All strains were gram-negative aerobic rods, 1.5 to 2.5 μm × 0.5 to 0.7μm, and had 1 to 7 polar flagella. No green fluorescent diffusible pigment was produced on King's medium B. Colonies were gray-white, slightly raised with smooth margins, and appeared within 3 days on nutrient agar. A hypersensitive reaction was observed on tobacco cv. Benshi 24 h after inoculation. All isolates were identified as B. glumae with Biolog similarity of 0.68 to 0.87 and FAMEs similarity of 0.65 to 0.91. Identification as B. glumae was confirmed by polymerase chain reaction (PCR) (3) primers BG1: 5'-ACACGGAACACCTGGGTA-3'; and BG2: 5'-TCGCTCTCCCGAAGAGAT-3'. Inoculation of intact plants of cv. Jiayue with cell suspensions containing 108 CFU/ml of the six strains individually produced seedling rot and grain rot symptoms. The bacterium was reisolated from symptomatic rice plants. B. glumae was first reported from Japan as the cause of grain rot of rice in 1967 (1) and was isolated from symptomatic rice seeds in 1987 in Taiwan, China. To our knowledge, this is the first report of B. glumae being isolated from healthy-looking rice seeds in China. This indicates that the pathogen is already in the mainland of China and there is a risk of a seedling rot outbreak if rice seedlings are raised indoors on a large scale for transplantation as it is in Japan. References: (1) T. Kurita and H. Tabei. Ann. Phytopathol. Soc. Jpn. 33:111,1967. (2) G. L. Xie et al. Acta Phytopathol. Sin. 32:114, 2002. (3) M. Yukiko et al. Int. J. Syst. Evol. Microbiol. 56:1031, 2006.