In 2011, the bacterial leaf streak disease of the monocotyledonous flowering plant, commonly known as bird of paradise (Strelitzia reginae), occurred in a nursery in Guangzhou, Guangdong Province, China. Lesions on diseased leaves began as water-soaked leaf spots or streaks near the central and secondary veins, eventually expanded along veins and became brown necrotic streaks. Occasionally, during wet conditions, seedlings were completely blighted. The disease incidence was about 12% in the nursery. Bacteria were consistently isolated on nutrient agar (NA) (4) from surface-sterilized symptomatic lesions and purified on NA. Three bacterial strains were tested for pathogenicity on S. reginae plants. Three plants were inoculated per bacterial strain (bacterial suspensions 107 CFU/ml in nutrient broth [NB] ) by wounding three young, fully expanded leaves (four wounds per leaf) with needle. Plants were placed in polyethylene bags 1 day before inoculation and maintained for 7 days after inoculation. Three control plants were inoculated with NB. Water-soaked areas on leaves were observed on all inoculated plants 7 days after inoculation. Within 10 days, brown streaks were observed. All strains induced similar symptoms as those observed on the plants in the nursery. Control plants showed no symptoms. For molecular identification, a near full-length sequence of the 16S rRNA gene was amplified from strain TNT1-1 (GenBank Accession No. JX901049.1) with primers 27F and 1492R (3), obtaining a PCR product of ~1,500 bp. A BLAST search in GenBank revealed the highest similarity (99.5%) to sequences of Burkholderia cepacia (FN178432.1 and FN178432.1). BIOLOG identification showed that TTN1-1 had the highest probability index of 0.85 and highest similarity index of 0.85 to B. cepacia. For biochemical characteristics, the strain was gram negative, anaerobic growth test negative, oxidase negative, catalase positive, did not produce fluorescent pigment on KB (4), did not grow on DIM agar (4), arginine dihydrolysis negative, nitrate reduction negative, starch hydrolysis negative, gelatin liquefaction negative, citrate, D-arabinose, L-fructose, trehalose, and maltose utilization positive, didn't produce acid from glucose, and grew on Tween 80 medium at 41°C. The above characteristics were identical to that of reference isolate B. cepacia ATCC 25416. Additionally, bacteria isolated on NA from the leading edge of lesions of inoculated plants with the strain were identical to the inoculated strain based on 16S rDNA sequence analysis, but no bacteria were recovered from the wounded sites on the control plants. Therefore, bacterial leaf streak of bird of paradise is caused by B. cepacia based on Koch's postulates. In contrast, two bacterial diseases on S. reginae were previously reported to be caused by Xanthomonas campestris (1) and B. gladioli (2) in the United States and Italy, respectively. A similar leaf streak disease on S. nicolai was caused by Acidovorax avenae subsp. avenae in the United States (5). To our knowledge, this is the first report of a leaf streak disease on S. reginae caused by B. cepacia.
References: (1) A. R. Chase and J. B. Jones. Plant Dis. 71:845, 1987. (2) G. Cirvilleri et al. Plant Dis. 90:1553, 2006. (3) I. M. Lee et al. Appl. Environ. Microbiol. 63:2631, 1997. (4) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001. (5) T. E. Seijo and N. A. Peres. Plant Dis. 95:1474, 2011.