Bacterial blight on Dracaena sanderiana caused by Burkholderia cepacia
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In 2018, severe bacterial blight was observed on Dracaena sanderiana plants imported and cultivated by a commercial nursery in Jinju, South Korea. This indoor plant is popularly grown for indoor air purification to prevent sick building syndrome (SBS). The diseased plants had severe blight symptoms, with leaf chlorosis and crumpling of stem and leaves. To identify the causal agent, we performed bacterial isolation, pathogenicity tests, physiological analysis, sequencing of the 16S rRNA region and recA gene, and phylogenetic analysis; the bacterial pathogen was identified as Burkholderia cepacia. This is the first report of bacterial blight on D. sanderiana caused by B. cepacia. Although there is no clear epidemiological information on the inoculum source, the recent occurrence of the disease indicates that B. cepacia is a potential threat to the production of indoor dracaena plants, which are increasingly used for air purification in SBS. Because D. sanderiana is grown in indoor living spaces, B. cepacia infection could threaten human health as well.
KeywordsDracaena sanderiana Blight Burkholderia cepacia 16S rRNA recA
Dracaena sanderiana, also called ‘Lucky Bamboo’ or ‘Ribbon Dracaena’, is a flowering plant in the family Asparagaceae. It is a small, shrubby plant with slim stems and flexible strap-shaped leaves. D. sanderiana is native to Cameroon in tropical West Africa, where it grows on the ground in tropical rainforests (Damen et al. 2018). It is a popular indoor plant that can survive in various indoor environments and has many cultivars (USDA, ARS 2008; Damen et al. 2018). D. sanderiana is often propagated from short cuttings in water. In Korea, it is called lucky bamboo because it is believed to bring happiness and prosperity when it is grown in houses and workplaces; this belief has made it more popular. Although it is attracting attention as an air purification plant to eliminate sick building syndrome (SBS), which is becoming a serious problem (Orwell et al. 2006; Dela Cruz et al. 2014), there are no accurate data on imports into South Korea.
In this study, we isolated and identified the causal plant pathogen from wilted D. sanderiana plants. We performed bacterial isolation, pathogenicity tests, molecular identification, and physiological tests. Here, we report the occurrence of bacterial blight caused by Burkholderia cepacia on D. sanderiana for the first time. The occurrence of this disease indicates that B. cepacia poses a potential risk to the production of ornamental D. sanderiana plants.
Bacteria were isolated as described previously (Choi and Kim 2013) with some modifications. Tissues (× 5 mm) from wilted stems of plants with leaf chlorosis were added to a 1.5-ml microtube containing 0.5 ml of sterile distilled water, macerated with a pipette tip, left to soak for 10 min, and vortexed vigorously to make a suspension. A 100 μl aliquot of a 1/10 serial dilution was spread on 1/10 tryptic soy broth agar (TSBA) and incubated at 28 °C for 3 days. The resulting dominant colonies were streaked onto new TSBA. Gram-negative, rod-shaped, and non-spore forming yellow colonies of bacteria were consistently isolated from infected tissues on TSBA. The yellow colonies were circular and opaque with smooth margins, and produced non-fluorescent yellow pigment. A representative isolate was deposited in the Korean Agricultural Culture Collection (KACC 21282).
Three isolates including KACC 21282 were tested for the tobacco leaf hypersensitive reaction and potato rot induction. All bacterial isolates were negative in the potato rot assays; however, they induced a hypersensitive reaction in tobacco leaves.
The physiological and biochemical characteristics of the bacteria were determined using the API 20NE system (BioMérieux, Marcy l’Etoile, France). The optical density of the bacterial suspension was adjusted as recommended by the manufacturer. In biochemical tests, KACC 21282 utilized d-glucose, l-arabinose, d-mannose, d-mannitol, N-acetyl-glucosamine, potassium gluconate, caprate, adipate, malate, trisodium citrate, and phenyl acetate, while it did not utilize d-maltose. The isolate was positive for catalase, oxidase, β-glucosidase, protease, and β-galactosidase, but negative for the production of arginine dihydrolase, urease, and indole. The isolate did not reduce nitrates to nitrites.
To confirm the identity of the bacteria, the 16S rRNA and recA genes were amplified with primer pairs 27mF (5′-AGAGTTTGATCMTGGCTCAG-3′) and 1492mR (5′-GGYTACCTTGTTACGACTT-3′) and BCR1 (5′-TGACCGCCGAGAAGAGCAA-3′) and BCR2 (5′-CTCTTCTTCGTCCATCGCCTC-3′), respectively (Lane 1991; Mahenthiralingam et al. 2000). DNA extraction and PCR amplification were as described previously (Choi et al. 2019). PCR was performed on a thermal cycler (T100; Bio–Rad, Hercules, CA, USA) using PCR premix (Bioneer, Daejeon, Korea), 1 μl genomic DNA, and 1 mM each primer, under the following conditions: 98 °C for 2 min; 30 cycles of 98 °C for 30 s, 55 °C for 30 s, and 70 °C for 1 min; and a final 4-min extension at 72 °C. The PCR products were examined by electrophoresis in 0.8% agarose gels, purified using Expin Gel SV (GeneAll Biotechnology, Seoul, Korea) and cloned using pGEM-T Easy Vector (Promega, Madison, WI, USA), according to the manufacturers’ instructions. Sequencing was performed with primers M13F and M13R using a BigDye Terminator Cycle Sequencing kit (Applied Biosystems, Foster City, CA, USA), following the manufacturer’s instructions. Using BLAST, searches revealed that the 16S rRNA (1,495 bp; GenBank accession no. MK779204) and recA gene (1,040 bp; MK779203) sequences of KACC 21282 shared 99.87 and 99.9% similarity with B. cepacia SE-1 (KF681774) (Zhu et al. 2016) and ATCC17759 (AF143788) (Mahenthiralingam et al. 2000; Mahenthiralingam and Vandamme 2005), respectively.
B. cepacia is reported to cause onion rot, and we also performed a pathogenicity test on onion bulbs. For onion bulb pathogenicity tests, three onion bulbs purchased from a market were each surface-disinfested with 70% ethanol, dried, and injected with 200 μl of bacterial suspension (~108 CFU/ml) of KACC 21282 using syringe infiltration. The bulbs were placed in plastic boxes at 100% relative humidity and incubated at room temperature for 7 days. Sterile distilled water was used as a negative control inoculation. KACC 21282 caused soft rot on the onion bulbs after 7 days after inoculation (Fig. 2c).
Combining the symptoms and results of the pathogenicity assay, API tests, and 16S rRNA and recA gene sequencing, the pathogen causing blight on D. sanderiana was identified as B. cepacia. This is the first report that B. cepacia causes blight on indoor D. sanderiana.
Isolates of the B. cepacia complex often cause pneumonia in immunocompromised patients with underlying lung diseases such as cystic fibrosis and chronic granulomatous diseases (Isles et al. 1984; Mahenthiralingam and Vandamme 2005). Some isolates cause bacterial soft rot on onions, while others are biological control agents with potential agricultural benefits (Parke and Gurian-Sherman 2001; Sotokawa and Takikawa 2004). The bacterium occurs naturally in various environments, including soil, the rhizosphere, urban habitats, and river water (Miller et al. 2002; Dalmastri et al. 2003; Ramette et al. 2005). Because D. sanderiana plant is grown in indoor living spaces, B. cepacia infection could pose a risk to human health. Although epidemiological information on the inoculum source is unclear, the recent occurrence of the disease indicates that B. cepacia is a potential threat to the production of indoor plants, which are increasingly used for air purification, such as in SBS.
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education of the Republic of Korea [2015R1A6A1A03031413].
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