Pseudomonas cichorii as the causal agent of midrib rot, an emerging disease of greenhouse-grown butterhead lettuce in Flanders

• Published in: Systematic and applied microbiology Vol. 32; no. 3; pp. 211 - 225
• Main Authors: Cottyn, Bart, Heylen, Kim, Heyrman, Jeroen, Vanhouteghem, Katrien, Pauwelyn, Ellen, Bleyaert, Peter, Van Vaerenbergh, Johan, Höfte, Monica, De Vos, Paul, Maes, Martine
• Format: Journal Article
• Language: English
• Published: München Elsevier GmbH 01-05-2009; Elsevier
• Subjects: Bacterial rot; Bacterial Typing Techniques; Bacteriology; Belgium; Biological and medical sciences; Butterhead lettuce; Dickeya sp; DNA, Bacterial - isolation & purification; DNA, Ribosomal - analysis; DNA-Directed RNA Polymerases - genetics; Fatty Acids - analysis; Fundamental and applied biological sciences. Psychology; Greenhouse; greenhouse production; Lactuca - microbiology; Lactuca sativa; Lactuca sativa var. capitata; lettuce; Microbiology; Miscellaneous; Molecular Sequence Data; Nucleic Acid Hybridization; pathogen identification; Pectolytic fluorescent pseudomonads; Plant Diseases - microbiology; plant pathogenic bacteria; plant rots; Polymerase Chain Reaction - methods; Polysaccharide-Lyases - metabolism; Pseudomonas; Pseudomonas - classification; Pseudomonas - genetics; Pseudomonas - isolation & purification; Pseudomonas - physiology; Pseudomonas cichorii; Pseudomonas fluorescens; Pseudomonas putida; RNA, Ribosomal, 16S - genetics; Sequence Analysis, DNA; Solanum tuberosum; Belgium; Bacterial rot; Greenhouse; Pseudomonas cichorii; Dickeya sp; Butterhead lettuce; Pectolytic fluorescent pseudomonads; Pseudomonadales; Emerging disease; Rot; Bacteria; Pseudomonadaceae; Pseudomonas
• ISSN: 0723-2020; 1618-0984
• DOI: 10.1016/j.syapm.2008.11.006

Bacterial midrib rot of greenhouse-grown butterhead lettuce (
Lactuca sativa L. var.
capitata) is an emerging disease in Flanders (Belgium) and fluorescent pseudomonads are suspected to play an important role in the disease. Isolations from infected lettuces, collected from 14 commercial greenhouses in Flanders, yielded 149 isolates that were characterized polyphasically, which included morphological characteristics, pigmentation, pathogenicity tests by both injection and spraying of lettuce, LOPAT characteristics, FAME analysis, BOX-PCR fingerprinting, 16S rRNA and rpoB gene sequencing, as well as DNA–DNA hybridization. Ninety-eight isolates (66%) exhibited a fluorescent pigmentation and were associated with the genus
Pseudomonas. Fifty-five of them induced an HR
+ (hypersensitive reaction in tobacco leaves) response. The other 43 fluorescent isolates were most probably saprophytic bacteria and about half of them were able to cause rot on potato tuber slices. BOX-PCR genomic fingerprinting was used to assess the genetic diversity of the
Pseudomonas midrib rot isolates. The delineated BOX-PCR patterns matched quite well with
Pseudomonas morphotypes defined on the basis of colony appearance and variation in fluorescent pigmentation. 16S rRNA and rpoB gene sequence analyses allowed most of the fluorescent isolates to be allocated to
Pseudomonas, and they belonged to either the
Pseudomonas fluorescens group,
Pseudomonas putida group, or the
Pseudomonas cichorii/
syringae group. In particular, the isolates allocated to this latter group constituted the vast majority of HR
+ isolates and were identified as
P. cichorii by DNA–DNA hybridization. They were demonstrated by spray-inoculation tests on greenhouse-grown lettuce to induce the midrib rot disease and could be re-isolated from lesions of inoculated plants. Four HR
+ non-fluorescent isolates associated with one sample that showed an atypical midrib rot were identified as
Dickeya sp.