First Report of a Leaf Spot Disease of Golden Dewdrop (Duranta erecta) Caused by Pseudomonas cichorii and a Xanthomonas Species in Florida

Duranta erecta (Verbenaceae) is used extensively in southern states as an ornamental shrub and has replaced boxwood as the most common short hedge accenting flower beds. Over the past 2 years, during warm wet periods, dark necrotic leaf spots have been observed on golden dewdrop plants in Florida. I...

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Veröffentlicht in:Plant disease 2013-06, Vol.97 (6), p.836-836
Hauptverfasser: Gumtow, R L, Khan, A A, Bocsanczy, A M, Yuen, J M F, Palmateer, A J, Norman, D J
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Sprache:eng
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Zusammenfassung:Duranta erecta (Verbenaceae) is used extensively in southern states as an ornamental shrub and has replaced boxwood as the most common short hedge accenting flower beds. Over the past 2 years, during warm wet periods, dark necrotic leaf spots have been observed on golden dewdrop plants in Florida. Isolations from these spots on Difco nutrient agar (NA) consistently yielded two types of bacterial colonies that were not always simultaneously present: 1) round butyrous, bright yellow and 2) flat cream-colored. Both were 2 mm in size after 48 h, gram-negative, and produced a hypersensitivity reaction (HR) on tobacco cv Hicks. Yellow colony bacteria were oxidase negative and non-fluorescent on King's medium B (KMB) (1). Cream-colored colony bacteria were oxidase positive and fluorescent on KMB. Three isolates of both types were selected for further study. Partial 16S rDNA sequencing and fatty acid analysis (FAME) MIDI Microbial Identification System (Microbial ID, Inc., Newark, DE) were used for identification of strains. The 16S rDNA primers used were; forward primer AMB14 5'-TCCAGCAATGCCGCGTGTGT-3' and reverse primer AMB13 5'-CATCCACCGCTTGTGCGGGT-3'. The PCR program consisted of an initial denaturing cycle of 95°C for 2 min followed by 30 cycles of denaturing at 95°C for 30 s, annealing at 60°C for 40 s and extension at 72°C for 1 min and one final extension at 72°C for 10 min. Using FAME analysis, the three strains of the cream-colored colony type were identified as Pseudomonas cichorii with high similarity values (0.907, 0.961, 0.819) and this corresponded well with the 16S rDNA sequences where 99% sequence identity was observed with P. cichorii strain JBC1 16S ribosomal RNA gene, partial sequence GenBank Accession No. JF951725. Two of the three yellow colony strains were identified by MIDI FAME profiles as Xanthomonas axonopodis pv. manihotis with similarity coefficients of 0.767 and 0.826. The third strain had a low similarity match to X. a. pv. carotae (0.541). The 16S rDNA sequencing of these strains showed 98% sequence identity to X. citri subsp. citri strain SA1 16S ribosomal RNA gene only, partial sequence identity JQ890091.1, thus indicating a possible undescribed X. axonopodis pathovar. To satisfy Koch's postulates, three golden dewdrop 'Golden Mound' plants were sprayed with a suspension of 10 CFU/ml of a 2-day NA culture of each strain, bagged for 24 h to raise humidity, and placed in a greenhouse. A strain of P. cichorii (P409) isolated from chr
ISSN:0191-2917
1943-7692
DOI:10.1094/PDIS-12-12-1117-PDN