December 3, 2005
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes, December 2005 [edited]
<http://www.apsnet.org/pd/searchnotes/2005/PD-89-1361C.asp>

Bacterial wilt of beans (Phaseolus vulgaris) caused by Curtobacterium flaccumfaciens in Southeastern Spain
A. J. Gonzalez, Laboratorio de Fitopatologia, SERIDA, Carretera de Oviedo s/n, 33300 Villaviciosa, Asturias. Spain; J. C. Tello, Departamento de Produccion Vegetal, Universidad de Almeria, 04120, Almeria, Spain; and M. R. Rodicio, Departamento de Biologia Funcional (Area de Microbiologia), Universidad de Oviedo, Julian Claveria 6, 33006 Oviedo, Asturias, Spain. Plant Dis. 89:1361, 2005; published on-line as DOI: 10.1094/PD-89-1361C.
Accepted for publication 29 Sep 2005.

Symptoms of bacterial wilt were observed on common beans (cv. Donna) in southeastern Spain. From samples collected in 4 different fields (coast of Granada), a bacterium was isolated with the following characteristics:
gram-positive, aerobic rods with yellow colonies, strictly oxidative, oxidase negative, galactose, sucrose, erythritol, mannitol, sorbitol and m-inositol were not used as a sole carbon source, and hydrolysis of casein was positive. These results coincide with what is expected for _Curtobacterium flaccumfaciens_ pv _flaccumfaciens_ (3).

One isolate from each field was selected for pathogenicity tests using 2 different methods. Bacterial suspensions (approximately 100 million CFU/ml) were spray-inoculated on bean seedlings of cv. Andecha (10 plants with 3 true leaves for each isolate). Beans were covered with transparent plastic bags for 2 days and held at 25 deg C and 80 percent relative humidity with a 12-h photoperiod. In addition, 10 healthy seeds of cv. Andecha were
soaked in bacterial suspensions (ca. 100 million CFU/ml) for 1 h and incubated at 25 deg C (2). Seedlings sprayed with distilled sterile water and seeds soaked in water served as controls. With both methods of inoculation, assays were conducted twice. Results were recorded after 3 weeks.

Symptoms that developed on plants after infection with the 4 isolates were similar to those observed in the field. They included golden yellow necrotic leaf lesions and wilting. Wilting was more pronounced in the field and when inoculation was performed by spraying seedlings rather than by soaking seeds. Control plants did not develop symptoms and grew bigger than the inoculated plants. 2 pathogenic isolates were identified through sequencing of the 16S rRNA gene. The genes were amplified by polymerase chain reaction (1) and their nucleotide sequences (1418 bp) proved to be identical (Accession No. AJ879110).

Comparison of these sequences with databases showed that they were also identical to those of _C. flaccumfaciens_ strains LMG 3645 and P 259/26 (Accession Nos. AJ312209 and AJ310414) and _Curtobacterium_ sp. strains 2384 and 3426 (Accession Nos. AY688359 and AY688360).

In Spain, the bean pathogen _C. flaccumfaciens_ was first isolated from seeds during 2001 (4). However, to our knowledge, this is the first report of damage caused by this bacterium in the field. Bacterial wilt has been recorded, but often not substantiated, in several countries from North and South America, Africa, Asia, Oceania, and Europe.

References:
(1) U. Edwards et al. Nucleic Acid Res. 17:7843, 1989.
(2) T. F. Hsieh et al. Plant Dis. 86:1275. 2002.
(3) K. Komagata and K.-I. Suzuki. Pages 1313-1317 in: Bergey's Manual of Systematic Bacteriology. Vol. 2. Williams and Wilkins, Baltimore, MD, 1986.
(4) J. L. Palomo et al. Page 154 in: XI Congreso de la Sociedad Espanola de Fitopatologia, Almeria, 2002.

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[_Curtobacterium flaccumfaciens_ subsp. _flaccumfaciens_ (Cff) grows throughout the water-conducting tissues of the plant and impedes water movement, resulting in a wilt. Symptom development is favored by temperatures greater than 32 deg C. Infection is often caused by the planting of infected seed, but Cff may also survive in infested crop debris. Cff bacteria are more confined to internal infection of plant vascular tissue, and apparently are not spread as readily by rain or movement of machinery among wet plants as compared to the halo blight
pathogen (_Pseudomonas syringae_ pv. _phaseolica_ ) or the common bacterial blight pathogen (_Xanthomonas campestris_ pv. _phaseoli_). Infection through natural openings on the plant are rare, but hailstorms and wounding favor infection. Cff is disseminated among fields by irrigation water and movement of infested crop debris or contaminated seed.

Disease management strategies include planting high-quality certified seed free from the bacterial wilt pathogen. There are varietal differences in their susceptibility to bacterial wilt, and resistant or tolerant varieties should be planted if available. A 2-year crop rotation to non-hosts such as small grains is recommended. Avoid reuse of irrigation water if possible and practice strict sanitation of crop debris and volunteer beans to reduce pathogen survival between bean crops. Antibiotic seed treatment can reduce surface contamination of seed, but chemical controls are most effective when integrated with sound cultural practices.

Links:
<http://www.agr.gc.ca/cal/epub/1758e/1758-0012_e.html>
<http://www.eppo.org/QUARANTINE/bacteria/Curtobacterium_flaccumfaciens/CORBFL_ds.pdf>
<http://highplainsipm.org/HpIPMSearch/Docs/BacterialWilt-DryBean.htm>
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12358698&dopt=Abstract>
<http://www.hort.uconn.edu/ipm/veg/htms/btbnbl.htm>
- Mod.DH]

[see also in the archive:
2003
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Plant pests, new data, EPPO 20030312.0608]