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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #281868
Title: New report of Lolium multiflorum and Rumex crispus as weed hosts of epiphytic populations of Psuedomonas sp., causal agent of yellow bud in onion in Geogia, USA

Author
item DUTTA, B - University Of Georgia
item GITAITIS, R - University Of Georgia
item LEWIS, K - University Of Georgia
item BOOTH, C - University Of Georgia
item LANGSTON, D - University Of Georgia
item Webster, Theodore
item RINER, C.M. - University Of Georgia
item EDENFIELD, J.D. - University Of Georgia

Submitted to: New Disease Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2013
Publication Date: 5/18/2013
Citation: Dutta, B., Gitaitis, R., Lewis, K., Booth, C., Langston, D., Webster, T.M., Riner, C., Edenfield, J. 2013. New report of Lolium multiflorum and Rumex crispus as weed hosts of epiphytic populations of Psuedomonas sp., causal agent of yellow bud in onion in Geogia, USA. New Disease Reports. 27:18.

Interpretive Summary: Yellow bud, an emerging bacterial disease of onion, has been spreading throughout the Vidalia onion-growing region in Georgia since 2007. Symptoms of yellow bud include intense chlorosis in emerging leaves and severe blight in the older leaves leading to stand loss and reduced bulb size. Like some other species sharing these traits, yellow bud strains have the ability to produce the toxin coronatine. In the spring of 2012, weed samples were collected from the edge of fields in three different counties (one fallow field where yellow bud was first observed in 2007 and two fields with onions currently expressing yellow bud symptoms). We detected the bacterium on Italian ryegrass (Lolium multiflorum L.) from all three locations and on curly dock (Rumex crispus L.) from only the fallow field. When 15-day old onion seedlings, cv. Century, were inoculated with a suspension from the weeds, 100% of the seedlings developed mild yellow bud symptoms, while control plants remained asymptomatic. Bacterial colonies were re-isolated from symptomatic seedlings and had similar characteristics to those described above. DNA sequences matched Pseudomonas sp. 7Y-1 and P. syringae pv. atropurpurea. This is the first report of these two weed species harboring epiphytic populations of yellow bud strains. Understanding the epidemiology of yellow bud should be helpful for developing disease management strategies.

Technical Abstract: Yellow bud, an emerging bacterial disease of onion (Allium cepa L.), has been spreading throughout the Vidalia onion-growing region in Georgia since 2007. Symptoms of yellow bud include intense chlorosis in emerging leaves and severe blight in the older leaves leading to stand loss and reduced bulb size. The causal agent is a Gram-negative, ice-nucleating, rod-shaped, aerobic bacterium. The bacterium possesses all the phenotypic characteristics of Pseudomonas syringae van Hall LOPAT group Ia, as it produces levan, is negative for oxidase, potato rot, and arginine dihydrolase and produces a hypersensitive reaction in tobacco. Like some other species sharing these traits, yellow bud strains have the ability to produce the toxin coronatine. However, unlike most P. syringae strains, the yellow bud bacterium does not produce a fluorescent pigment on King’s medium B agar. In the spring of 2012, weed samples were collected from the edge of fields in three different counties (one fallow field where yellow bud was first observed in 2007 and two fields with onions currently expressing yellow bud symptoms). The assay detected the bacterium on Italian ryegrass (Lolium multiflorum L.) from all three locations and on curly dock (Rumex crispus L.) from only the fallow field. When 15-day old onion seedlings, cv. Century, were inoculated with a suspension of 1 × 108 colony forming units (CFU)/ml, 100% of the seedlings developed mild yellow bud symptoms. Ten control plants inoculated with sterile water remained asymptomatic. Bacterial colonies were re-isolated from symptomatic seedlings. The non-fluorescent colonies recovered had similar characteristics to those described above. Universal primers fD1 and rD1 and cfl1 and cfl2 were used to amplify the 16S rRNA and coronofactate ligase genes, respectively. Amplified products were sequenced. DNA sequences were BLAST searched in GenBank. The nucleotide sequences of the weed strains matched Pseudomonas sp. 7Y-1 and P. syringae pv. atropurpurea (98 to 99% similarity with 16srRNA and 94 to 99% by coronofactate ligase gene). Additional samples of Italian rye grass and curly dock were collected from plants flagged during the earlier visit. Bacterial colonies were isolated from the weed washes and again identified as non-fluorescent stains in LOPAT group Ia. This is the first report of these two weed species harboring epiphytic populations of yellow bud strains. Understanding the epidemiology of yellow bud should be helpful for developing disease management strategies.