First Report of Pectobacterium carotovorum subsp

Short Communication
First Report of Pectobacterium carotovorum
carotovorum on Tomato Plants in Tunisia
subsp.
Khaled Hibar, Laboratoire de Phytopathologie, Institut Supérieur Agronomique de
Chott-Mariem, 4042, Chott-Mariem, Tunisia, Mejda Daami-Remadi, Laboratoire
de Phytopathologie, Centre Régional des Recherches en Horticulture et Agriculture
Biologique, 4042, Chott-Mariem, Tunisia, and Mohamed El Mahjoub, Laboratoire
de Phytopathologie, Institut Supérieur Agronomique de Chott-Mariem, 4042, ChottMariem, Tunisia.
__________________________________________________________________________
ABSTRACT
Hibar, K., Daami-Remadi, M., and El Mahjoub, M. 2007. First report of Pectobacterium
carotovorum subsp. carotovorum on tomato plants in Tunisia. Tunisian Journal of Plant
Protection 2: 1-5.
During winters of 2005 and 2006, a severe outbreak of a stem rot disease occurred on tomato plants in
greenhouses in Sidi Bouzid, Chott-Mariem and Mereth regions; disease incidence was estimated to
respectively 20-25%, 30-35% and 90-100%. Isolations from rotted stems on King’s medium B showed
development of a bacterium characterized by white to cream colonies. Using some biochemical tests,
all bacterial isolates were identified as Pectobacterium carotovorum subsp. carotovorum.
Pathogenicity tests demonstrated the development of soft-rot symptoms on inoculated tomato plants. In
Tunisia, this bacterium is well known as a potato soft rot pathogen, but this is the first report of an
occurrence and an outbreak of a bacterial stem rot disease on tomato plants caused by P. carotovorum
subsp. carotovorum.
Keywords: Tomato, stem rot, Pectobacterium carotovorum subsp. carotovorum, Tunisia
__________________________________________________________________________
vely Central and Southern Tunisia, a
severe outbreak of a bacterial stem rot
disease occurred on tomato plants.
Tomato cultivars on witch symptoms
were observed were ‘Amel’ and
‘Ventura’. The disease symptoms
appeared under high humidity and
temperature conditions occurring in
greenhouses cultivated by tomato crops.
Characteristic symptoms of the disease
that we observed were darkening and
water soaking of the stem (Fig. 1A) and
browning in the vessel and pith of the
diseased plants. Stem and leaves may
completely rot (Fig. 1B) and whole the
plant may wilt (Fig. 1C) and even
collapse.
Disease incidence was estimated to
be approximately 20-25%, 30-35%, and
90-100% in greenhouses of the regions of
Pectobacterium carotovorum subsp.
carotovorum (syn. Erwinia carotovora
subsp. carotovora) mainly affects crops
in subtropical and temperate regions and
has likely among the phytopathogenic
bacteria the widest host range. It is the
causal agent of bacterial soft rot, a severe
and devastating disease of many
economically important food crops such
as potato, tomato, pepper, eggplant, and
cabbage (1, 2, 4, 5, 6, 7, 8, 9, 14, 15, 16,
17).
During the winters of 2005 and 2006,
in the regions of Sidi Bouzid, ChottMariem and Mereth located in respectiCorresponding author: M. Daami-Remadi
[email protected]
Accepted for publication 18 July 2007.
Tunisian Journal of Plant Protection
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Vol. 2, No. 1, 2007
Pathogenicity tests were performed
using four randomly selected isolates.
These bacterial isolates were suspended
in distilled water (108 cfu/ml) and needlepunctured to the stems of ten healthy
tomato plants (5-week-old cv. Amel). All
plants were covered with polyethylene
bags and incubated for 72 h at 25°C.
These bacterial isolates were also tested
for their ability to induce soft rot on
potato tubers. Ten healthy tubers (cv.
Spunta) were surface disinfected in
sodium hypochlorite (10 %) for 3 min,
rinsed with sterile distilled water and
inoculated with the bacterial suspension.
Results of the pathogenicity tests showed
that within 72 h after inoculation, watersoaking and soft-rot symptoms were
observed on inoculated tomato plants.
Bacteria with the same characteristics as
those inoculated were successfully reisolated from diseased tomato plants.
Control plants inoculated with water
remained healthy. The bacterial isolates
caused also soft rot on potato tubers
within 48 h at 30°C (Fig. 1D).
According to results of biochemical
and pathogenicity tests, all bacterial
isolates tested in the present study were
identified as Pectobacterium carotovorum
subsp. carotovorum. This identification
would need confirmation by molecular
tests. In Tunisia, P. carotovorum subsp.
carotovorum is well known as a pathogen
of potato (11, 12, 13) and it was detected
in many other Mediterranean countries (2,
4, 7, 17). But this is the first time to report
the occurrence and the outbreak of this
bacterial disease on tomato plants in
Tunisia.
The damage of this disease in
greenhouse crops can be reduced by an
early detection and an avoidance of
wounding on plants. Infected plants
should be destroyed and the crop treated
with fixed copper sprays. After cropping,
plant residues should be carefully
removed and the soil exposed to
solarization for at least 45 days during the
summer (7).
Sidi Bouzid, Chott Mariem, and Mereth,
respectively. The high level of attack,
especially in the region of Mereth,
seemed to be due to potato cropped
before settling tomato greenhouses. The
objective of this study was to identify the
causal agent of this emergent tomato
disease.
Isolations were performed from
rotted stems of tomato plants on King’s
medium B. Bacteria consistently isolated
from the diseased tissues produced white
to cream colonies on the medium as
described by Cetinkaya-Yildiz et al. (5).
On the semi-selective medium crystal
violet sodium polypectate (CVP) (3),
bacterial isolates showed pits formation.
On modified crystal violet sodium
polypectate (CVPB) double layer
medium, with 2,3,5-triphenyltetrazolium
chloride and L-asparagine in the basal
medium and bromthymol blue in the
upper, these isolates formed red to pink
colonies with pits. These cavities were
also observed when bacteria were isolated
on Miller-Schroth (MS) medium (10).
Biochemical tests were applied for all
the isolates. They were performed
according to methods reported by De
Boer and Kelman (6) and Schaad et al.
(14). On the basis of these biochemical
tests, bacteria obtained from purified
colonies, were Gram negative, oxidase
negative, arginine dyhidrolase negative,
catalase
positive,
and
facultative
anaerobic. Four representative isolates
fermented glucose and reduced nitrates to
nitrites. All isolates were resistant to
erythromycin in an antibiotic disk (15 µg)
assay. Negative results were obtained by
utilization of α-methyl glycoside,
reducing substance from sucrose, and
producing indole from tryptophane and
phosphathase activity. Positive results
were obtained by pectate, aesculin, and
gelatine liquefaction for all tested
isolates. Acid was produced from
glucose, sucrose, mannitol, mannose,
lactose, raffinose, melibiose, trehalose,
and L(+) arabinose but not from Darabinose, sorbitol, inulin, and maltose.
Tunisian Journal of Plant Protection
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Vol. 2, No. 1, 2007
A
B
C
D
Fig. 1. A: Soft rot caused by Pectobacterium carotovorum subsp. carotovorum (Pcc) on the stem of a tomato plant
(cv. Amel); B: Extending soft rot on the stem of a tomato plant (cv. Amel) infected with Pcc; C: Yellowing and
wilting of a tomato plant infected by Pcc; D: Typical soft rot induced on potato tubers (cv. Spunta) inoculated by Pcc
after 48 h of incubation at 30°C.
Tunisian Journal of Plant Protection
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Vol. 2, No. 1, 2007
__________________________________________________________________________
RESUME
Hibar K., Daami-Remadi M. et El Mahjoub M. 2007. Première description de Pectobacterium
carotovorum subsp. carotovorum sur plants de tomate en Tunisie. Tunisian Journal of Plant
Protection 2: 1-5.
Durant l’hiver de 2005 et de 2006, une éruption sévère d’une pourriture de la tige a eu lieu sur des
plants de tomate dans des serres situées dans les régions de Sidi Bouzid, Chott Mariem et Mereth;
l’incidence de la maladie a été estimée à 20-25%, 30-35% et 90-100% respectivement. Les isolements,
réalisés sur milieu King B à partir des tiges pourries, ont montré le développement d’une bactérie
caractérisée par des colonies blanches à crèmes. En se basant sur des tests biochimiques, tous les isolats
collectés ont été identifiés comme étant Pectobacterium carotovorum subsp. carotovorum. Les tests de
pathogénie ont montré le développement de symptômes de pourriture molle sur les plants de tomate
inoculés. En Tunisie, cette bactérie est bien connue comme un pathogène causant une pourriture molle
de la pomme de terre, mais il s’agit ici de la première description de l’occurrence et de l’éruption d’une
pourriture bactérienne de la tige sur des plants de tomate causée par P. carotovorum subsp.
carotovorum.
Mots clés: Tomate, pourriture de la tige, Pectobacterium carotovorum subsp. carotovorum, Tunisie
__________________________________________________________________________
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___________________________________________________________________________
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