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Date: November, 2007
Source: The American Phytopathological Society, Plant Disease 2008; 91(11): 1514 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-91-11-1514C>

First report of ear soft rot of corn (Zea mays) caused by Burkholderia gladioli in the United States

During the summer of 2005, an uncharacterized disease was observed on sweet corn commercially grown in Sunflower County, Mississippi. Initial symptoms developing at the base of the ear on interior husk leaves were brown, water-soaked, irregular lesions. These gradually enlarged up to 10 cm (3.9 in) in diameter. Market value was significantly affected when the corn ears had visible symptoms of this disease. Bacterial cell streaming was observed at a magnification of 675 times from the diseased husk. A bacterium was consistently isolated from lesions.

Isolates MS102 and MS103, which were chosen for further characterization, were Gram negative, and biochemical characteristics were the same as those described previously for _Burkholderia gladioli_. Confirmation was made by polymerase chain reaction (PCR) analysis of the nearly complete 16S rRNA gene (1471 base pairs). DNA sequence analysis demonstrated that the 16S rRNA gene of the bacterium shared highest identities (99.4 to 99.6 per
cent) with that of 3 _B. gladioli_ strains. A product (approximately 300 bp) characteristic of _B. gladioli_ also was obtained from both isolates using species-specific PCR.

To confirm pathogenicity, cell suspensions of the isolates were injected into interior husk leaves of field-grown sweet corn. Control corn ear husks were injected with phosphate buffer. After 3 days, ear rot symptoms were observed on all plants inoculated with the isolates but not those injected with phosphate buffer. Cell suspension of isolates dropped on non-wounded husks also incited the same symptoms as those inoculated with a syringe.
Koch's postulates were fulfilled with reisolation from the inoculated tissues. The identity of the reisolated pathogen was proved by sequencing the 16S rRNA gene.

This disease was previously reported in Brazil. To our knowledge, this is the 1st report of _B. gladioli_ causing a disease of corn in the United States. Although the impact of this disease was not observed from 2005 to
2006 because of dry weather and rotation to other crops in the affected field, there is a potential that the bacterium could become established in corn-producing areas as a member of the corn ear rot complex if environmental conditions are favorable.

[byline: SE Lu, et al]

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communicated by:
ProMED-mail
<promed@promedmail.org>

[_B. gladioli_ (formerly _Pseudomonas gladioli_ or _P. marginata_) was initially described in 1921 as a soil inhabiting phytopathogen of gladioli and other flowers. It causes, for example, bulb soft rot of onion; scab, soft and corm rots of gladiolus, iris, freesia, and other flower crops; soft rot of orchids with up to 50 per cent loss; grain rot, panicle blight, and leaf-sheath browning of rice plants (sometimes together with other species in the genus). The pathogen is spread in soil and water, by mechanical means (including on insects), and with infected plant material.
Disease management includes the use of clean planting material and cultural practices such as frequent disinfection of tools, insect control, and reduction of free moisture in plantings.

_B. gladioli_ is a heterogeneous species with phenotypic and genetic variability and has been divided into 3 pathovars (pv. _gladioli_, pv.
_alliicola_ and pv. _agaricicola_) based on their host ranges. Strains assisting in nitrogen fixation have been found in the rhizospheres of a number of cereals and sugarcane. Some strains are nematode and fungal antagonists and can be used in biocontrol (for example for _Fusarium_ species); some strains are plant growth promoters. Strains producing human toxins or associated with infections in humans have also been reported.

A number of fungal pathogens causing ear and stalk rots are known for maize. Bacterial stalk and ear rots are less frequent and may be caused by one of several species that live as saprophytes on plant debris in the soil, for example _Erwinia_ species. They are sometimes found in maize crops after accidental flooding. However, such a trigger is not being reported here and may not be needed for _B. gladioli_ ear rot.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html>  and
<http://healthmap.org/promed?v=40,-97.6,4>
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Mississippi counties:
<http://mapsofworld.com/usa/states/mississippi/mississippi-county-map.html>
Pictures
Panicle blight on rice:
<http://www.lsuagcenter.com/mcms/webtools/image.aspx?Watermark=bgB1AGwAbAA=&ResourcePath=/NR/rdonlyres/8CB2201D-902F-4461-89C4-6A4F31B64260/14798/PBL.jpg> 

Bacterial soft rot on onion:
<http://mtvernon.wsu.edu/path_team/Disease%20Gallery/dg95L.jpg>
Scab on gladiolus:
<http://www.ojdinfo.nsw.gov.au/Hort/ascu/zeck/others.pic8.jpg>
Links
_B. gladioli_ on rice:
<http://sciencelinks.jp/j-east/article/200618/000020061806A0638165.php>  and
<http://www.lsuagcenter.com/en/communications/publications/agmag/Archive
/2003/Fall/Biotechnology+and+Control+of+Rice+Diseases.htm> 

_B. gladioli_ on onion:
<http://www.publish.csiro.au/?paper=AP05024>
_B. gladioli_ on orchids:
<http://apsjournals.apsnet.org/doi/abs/10.1094/PD-89-1273>
Diseases of gladiolus including scab:
<http://www.wvu.edu/~agexten/hortcult/flowers/disglads.htm>
Biocontrol applications:
<http://www.patentstorm.us/patents/4880745-description.html>
Toxin-producing strains:
<http://www.jstage.jst.go.jp/article/mandi/47/12/47_915/_article/-char/en>
PCR detection and differentiation of _B. gladioli_:
<http://www.springerlink.com/content/1x78ql1eg4g3gpvd/>
Taxonomy of the genus _Burkholderia_ with species list:
<http://www.bacterio.cict.fr/b/burkholderia.html>  and
<http://www.dsmz.de/microorganisms/bacterial_nomenclature_info.php?genus=BURKHOLDERIA&show_all_details=1> 

Bacterial ear rots on maize after flooding:
<http://www.pioneer.co.nz/pdf%20files/maize%20pdfs/342.pdf>
List of maize diseases and pathogens:
<http://www.apsnet.org/online/common/names/corn.asp>.  - Mod.DHA]

[see also in the archive:
2007
---
Burkholderia cocovenenans foodborne illness - Indonesia (Central Java)
20070802.2493]

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