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Date: June 2007
Source: Plant Disease 91(6), 711-8 [edited] <http://www.apsnet.org/pd/current/>

Isolation and identification of the causal agent of brown stalk rot, a new disease of maize in South Africa

During 2004 to 2005, an unreported disease of maize (_Zea mays_) was observed on commercial fields in the Northwest and Mpumalanga Provinces of South Africa. Infected plants were stunted, with a vertical crack at the 1st internode. Inside the stem, a dark-brown, narrow lesion was present along the crack. Internal browning inside the stem extended upward, reaching the top internode in some plants.
Seed cobs were underdeveloped. Diseased plants were scattered in the fields and 10 to 70 percent of the crop was affected.

Gram-negative, facultatively anaerobic bacteria were consistently isolated from diseased tissues. Pathogenicity tests established that representative strains induced disease symptoms similar to those observed on maize plants in the field. Physiological and biochemical characterization using the API 20E and API 50CHE systems and 16S rRNA gene sequence analyses showed that the strains belonged to the genus _Pantoea_.

The results of these tests also separated the strains into 2 groups.
The 1st group, giving a positive reaction in the indole test, was similar to _P. ananatis_. The 2nd group of strains was indole negative and resembled _P. agglomerans_. The fluorescent amplified fragment length polymorphism (F-AFLP) genomic fingerprints generated by the indole-positive strains and _P. ananatis_ reference strains were similar and clustered together in the dendrogram, confirming that the indole-positive bacteria causing brown stalk rot on maize were _P. ananatis_. The F-AFLP fingerprints produced by the indole-negative strains were distinctly different from those generated by _P. ananatis_, _P. agglomerans_, _P. dispersa_, _P. citrea_, _P. stewartii_ subsp. _stewartii_, and _P. stewartii_ subsp. _indologenes_. The results indicated that indole-negative bacteria causing brown stalk rot on maize might belong to a previously undescribed species of the genus _Pantoea_.

This is the 1st report of a new disease on maize, brown stalk rot, caused by 2 bacterial species, _P. ananatis_ and an undescribed _Pantoea_ sp.

[Byline: Goszczynska, T. et al.]

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[In addition to the above, the authors also report (see link below):
"In spray inoculations, all strains caused chlorotic, slightly rotten lesions on maize leaves. When bacterial suspension was injected into the 2nd stem node, discoloration of the stalk at the node was observed 3-4 weeks after inoculation. The rot spread upwards, causing browning of vascular tissues and rot of the leaf sheaths. Inoculated plants produced seed from which _P. ananatis_ was isolated. This is the 1st report worldwide of bacterial stalk rot of maize caused by _P. ananatis_, and transmission of this pathogen in maize seed." Thus Koch's postulate has been satisfied which requires that to prove a pathogen to be the cause of a disease it needs to be isolated, cultured and the host re-inoculated resulting in the same symptoms.

Species of the genus _Pantoea_ cause a variety of diseases on a range of crops. For example, _P. citrea_ is the causal agent of Pink disease of pineapple; Center rot of onion is caused by _P. ananatis_; _P. stewartii_ causes Stewart's bacterial wilt on maize, an important insect-borne disease in parts of the USA and Europe. A bacterial blight of _Eucalyptus_ and a leaf blotch disease of sudangrass have also been associated with _Pantoea_ spp. The genus belongs to the family of _Enterobacteriaceae_ which also comprises genera pathogenic to humans or animals, but the majority of _Pantoea_ spp. are plant-associated.

There are 3 important findings in this work: 1st report of Brown stalk rot, a new disease of maize; 1st report of a new as yet unclassified species of _Pantoea_; 1st report of seed-transmission of _P. ananatis_ in maize.

Map of South Africa:
<http://www.safarinow.com/destinations/South-Africa/south-africa-map.gif>

Pictures
Symptoms of Stewart's wilt on maize:
<http://www.invasive.org/images/768x512/0454008.jpg>
Pink disease of pineapple:
<http://www.apsnet.org/online/feature/pineapple/image/pink1sm.jpg>

Links:
Additional information on Brown stalk rot by the authors:
<http://155.240.199.39/v-arcroot/institutes/ppri/main/news/downloads/pprinews64.pdf>

Diseases associated with _Pantoea_:
<upetd.up.ac.za/thesis/available/etd-02092006-110117/unrestricted/00front.pdf>
_Pantoea_ taxonomy:
<http://www.bacterio.cict.fr/p/pantoea.html>
Information on Stewart's bacterial wilt of maize:
<http://www.ca.uky.edu/agc/pubs/ppa/ppa33/ppa33.htm> and <http://nu-distance.unl.edu/Homer/disease/agron/corn/CoStewWlt.html>
Information on Pink disease of pineapple:
<http://www.apsnet.org/online/feature/pineapple>
_Pantoea_ associated with bacterial blight of _Eucalyptus_:
<http://www.pestalert.org/espanol/viewArchNewsStory.cfm?nid=140>
- Mod.DHA]

[see also in the archive:
2004
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Quarantine pests, new data - EPPO 20040107.0072
2003
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Plant pests, new data, EPPO (03) 20030728.1853 2000
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Plant pathogens, intercepts, EPPO 20000204.0170
1999
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Plant pests - Russia 19991202.2114]

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