Skip to main content
ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #295255
Title: First report of bacterial blight of sugar beet caused by Pseudomonas syringae pv. aptata in Georgia, USA

Author
item DUTTA, B - University Of Georgia
item INGRAM, T - University Of Georgia
item GITAITIS, R - University Of Georgia
item LANGSTON, D - University Of Georgia
item BRENNEMAN, T - University Of Georgia
item Webster, Theodore
item Davis, Richard

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2014
Publication Date: 8/15/2014
Citation: Dutta, B., Ingram, T., Gitaitis, R.D., Langston, D.B., Brenneman, T., Webster, T.M., Davis, R.F. 2014. First report of bacterial blight of sugar beet caused by Pseudomonas syringae pv. aptata in Georgia, USA. Plant Disease. 98:1423. doi: org./10.1094/PDIS-03-14-0235-PDN.

Interpretive Summary: A recent push for alternative fuel sources to be grown in a manner that does not interfere with current crop production rotations, makes winter production of sugarbeet [Beta vulgaris L.] in Georgia an attractive crop. Preliminary studies are promising in terms of yield and industrial sugar production. Growing this crop, a summer annual in its normal production areas of the Midwest and Northwest U.S., the potential pests when grown as a winter crop are not well characterized. In field plots, there was a disease outbreak of suspected bacterial origin in Tift County, Georgia in December 2012 and resulted in approximately 35% disease incidence. Foliar symptoms included circular to irregularly-shaped spots with tan centers and dark margins. After 48-h of incubation, cream-colored, fluorescent, round colonies with smooth margins were isolated, and isolates belonged to Pseudomonas syringae van Hall LOPAT group Ia. These isolates showed similar characteristics to isolates recovered from a sugarbeet seedlot. When two-week old seedlings of sugarbeet were inoculated by spraying with a suspension, 100% of the seedlings developed symptoms (water soaked lesions that developed into necrotic spots) after 10 days of planting under greenhouse conditions (~30°C and ~80% RH). Five control seedlings inoculated with sterile water did not develop any symptoms. Bacterial colonies were re-isolated from symptomatic seedlings that showed similar characteristics to those described above. The phenotypic, genotypic and pathogenicity data indicated that these strains were P. syringae pv. aptata. To our knowledge, this is the first report of P. syringae pv. aptata in sugarbeet in Georgia. The fact that a P. syringae pv. aptata strain was also isolated from a sugarbeet seedlot suggests that the pathogen may have been introduced through contaminated seeds.

Technical Abstract: Sugarbeet [Beta vulgaris L.] is not currently a commercial crop in Georgia, but experimental plantings as a winter rotational crop are promising in terms of yield and industrial sugar production. A disease outbreak of suspected bacterial origin occurred in some plots of sugarbeet [experimental lines: Betaseed energy beet ‘BTS ENC115’, ‘BTS EGC184’, ‘BTS EGC195’, and ‘BTS 1EN6702’] in Tift County, Georgia in December 2012 and resulted in approximately 35% disease incidence. Foliar symptoms included circular to irregularly-shaped spots with tan centers and dark margins. Forty leaves (n=10/experimental line) with leaf spot symptoms were collected and bacterial isolations were made on King’s medium B. After 48-h of incubation, cream-colored, fluorescent, round colonies with smooth margins were isolated. The isolates were gram-negative, oxidase-negative, non-pectolytic on potato, arginine dihydrolase-negative, produced levan, and gave a hypersensitivity response on tobacco (HR). These characteristics indicated that the isolates belonged to Pseudomonas syringae van Hall LOPAT group Ia. Additionally, isolates showing similar characteristics were also recovered from a sugarbeet seedlot (n = 500 seeds) [BTS 1EN6702]. Both 16S rRNA and 16S-23S rRNA (internal transcribed regions) from five isolates (four foliar and one seedborne) were amplified and resultant PCR products were sequenced and BLAST searched in GenBank. The nucleotide sequences of 16S rRNA matched with Pseudomonas syringae pv. syingae (Accession number JQ071937.1) with 98-99% sequence identity. In addition, the sequence of 16S-23S rRNA matched with both Pseudomonas syringae pv. syingae (Accession number AY342167.1) and Pseudomonas syringae pv. aptata (Accession number CP000075.1) with 96 to 98% and 97 to 99% sequence identity, respectively. Isolates also had =89% and =99% similarity with P. syringae pv. aptata and P. syringae pv. syringae, respectively in BIOLOG (Biolog, Hayward, CA). When two-week old seedlings of sugarbeet [Beta EGR099] (n = 10/isolate/experiment) were inoculated by spraying with a suspension of 1 × 108 CFU/ml, 100% of the seedlings developed symptoms (water soaked lesions that developed into necrotic spots) after 10 days of planting under greenhouse conditions (~30°C and ~80% RH). Five control seedlings inoculated with sterile water did not develop any symptoms. Bacterial colonies were re-isolated from symptomatic seedlings that showed similar characteristics to those described above. The phenotypic, genotypic and pathogenicity data indicated that these strains were P. syringae pv. aptata. To our knowledge, this is the first report of P. syringae pv. aptata in sugarbeet in Georgia. The fact that a P. syringae pv. aptata strain was also isolated from a sugarbeet seedlot suggests that the pathogen may have been introduced through contaminated seeds