Scientific bulletin 319 - May 2009
Bacteria that protect strawberries
© IRD / Michel Jégu
© Univ.Tunis / N. Sadfi Zouaoui
M
ore than 225 kinds
of plant −tomatoes,
grapes, courgettes,
lettuce− fall victim
to grey mould. It is
the most devastating
disease of strawberries
in particular.
What organism is
responsible? A fungus
called Botrytis cinerea
which sets off premature
rotting of the fruit.
Currently, chemical
fungicides are the only
effective controlling
agents against this
parasite. A biological
alternative is
nevertheless possible.
There are specific
bacteria that can reduce
or even stop this mould
completely. Researchers
from the Tunis Faculty
of Sciences, supported
by the IRD1, recently
identified two strongly
grey-mould resistant
bacteria of the genus
Bacillus in Tunisian
soils. The team has
developed a product
based on these bacteria
which substantially
improves strawberry
postharvest storage life.
At a time when chemicalagent resistant fungal
strains have emerged,
this biological approach
offers new prospects for
strawberry producers
throughout the world.
Grey mould spreads from fruit to fruit and can decimate a strawberry crop, especially
during storage.
The ravaging fungus Botrytis cinerea
can devastate entire crops of fruit
and vegetables, making them unfit for
consumption. Strawberries are particularly badly hit: from the Mediterranean
rim to Asia and over to Mexico and the
United States, the losses caused by
this fungal disease, also called grey
mould, can reach 25% of the global
harvest of untreated strawberries.
Control methods exist.
Dressing with synthetic fungicides is
still the only treatment currently employed. Apart from the problems of toxic
residues left on fruit, which increasingly
cause concern among consumers, this
practice has its limits: the parasite has
developed strains resistant to the chemical substances used, making such
agents totally ineffective. This difficulty
prompts interest in a biological alternative, which does not create risk of
genetic mutation of the fungus. Biological treatment consists simply in introducing an agent into the plant’s environment (for instance another fungus,
or a bacterium), harmless for the plant
itself, which will steadily take the place
of the B. cinerea in the ecosystem.
Highly effective bacteria.
Researchers from the Faculty of
Sciences of Tunis, supported by the
IRD, recently demonstrated that halophilic bacteria2, adapted to highly saline environments, can reduce grey
mould on the strawberries by at least
50% or even remove it completely. The
Tunisian researchers first isolated new
strains of bacteria −non pathogenic for
either the plant or humans, and known
for their resistance and effectiveness
against the parasites Bacillus subtilis
and Bacillus pumilus− in different regions of Tunisia. They therefore collected soil samples from sebkhas and
chotts3, hypersaline ecosystems particularly frequent in arid regions such
as North Africa and the Middle East. In
work to support the Tunisian team, the
IRD researchers traced the phylogeny,
or evolutionary history, of the newly
isolated bacteria.
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You can find the IRD photos concerning this bulletin, copyright free for the press, on www.ird.fr/indigo
Sadfi-Zouaoui N. Biological
control of grey mould
in strawberry fruits by
halophilic bacteria, Journal
of Applied Microbiology,
106(3), 2009. doi:10.1111/
j.1365-2672.2008.04053.x
KEY WORDS :
Strawberry, grey mould,
biological control, Tunisia
Gaëlle Courcoux - DIC
Translation - Nicholas Flay
1. These bacteria are known to be effective
against B. cinerea. Substances they produce are toxic for the fungi and extracellular hydrolytic enzymes they secrete are
able to alter the fungal cells.
2. The IRD has supported this research
work as part of a contract with the joint
Franco-Tunisian committee for academic
cooperation, Comité mixte de coopération
universitaire franco-tunisien. The research
was done jointly with the Institut National
de Recherche Agronomique de Tunisie
(INRAT) and the Faculté Universitaire des
Sciences Agronomiques of Gembloux in
Belgium.
3. A sebkha is a hollow once occupied by
the sea which, on receding, left the soils
loaded with salt. A chott is a salt lake
whose high salinity is the result of strong
evaporation.
Vincent Coronini
+33 (0)4 91 99 94 87
presse@ird.fr
INDIGO,
IRD PHOTO LIBRARY :
Strawberries treated with the Bacillus
(right) are preserved much better than
non-treated ones (left).
© IRD / Vincent Simonneaux
PRESS OFFICE :
Daina Rechner
+33 (0)4 91 99 94 81
indigo@ird.fr
www.ird.fr/indigo
producers faced with the effects of
fungal resistance to chemical substances. The researchers are now
continuing their work, aiming for maximum improvement of the process with
a view to its homologation and release
on to the market.
© Univ.Tunis / Najla Sadfi Zouaoui
Scientific bulletin 319 - May 2009
Commercial application trials.
The researchers subsequently asCONTACTS :
sessed the commercial potential of
these bacteria for the preservation of
Najla SADFI ZOUAOUI
strawberries under postharvest stoLaboratoire Microorganismes
rage, a crucial phase in the developet Biomolécules Actives
ment of the disease. Indeed it is during
Address :
Faculté des Sciences de Tunis storage that a mould colony, propagating from fruit to fruit, can take hold of
Université de Tunis El Manar
an entire crop. The effectiveness of bioTél. : + 216 71 872 600
logical agents for strawberry plants has
sadfi.najla@planet.tn
already been demonstrated. However,
to date, very little research work has
Marie-Laure FARDEAU
examined their performance during
Chercheur à l’IRD
postharvest storage of the fruit.
Laboratoire Microbiologie et
The Tunisian researchers thus conducBiotechnologie des Environted warehouse trials with a commercial
nements Chauds (LMBEC)
application based on the two bacteria,
UMR (IRD, universités Aixon strawberries from the Cap-Bon reMarseille I et II)
gion in the north-east of the country.
Address :
The testing ran for three seasons, from
Université de la Méditerranée
2006 to 2008. This product is promising,
163 avenue de Luminy
as it successfully saved a substantial
13288 Marseille cedex 9
proportion of the harvests. Compared
Tél. : 33 (0)4 91 82 85 76
with untreated and chemical fungicidemarie-laure.fardeau@ird.fr
treated strawberries, those receiving
bacteria showed a significant reduction
REFERENCES :
in grey mould.
This biological alternative therefore
Essghaier B., Fardeau M.L.,
holds considerable ecological and
Cayol J.L., Hajlaoui M.R.,
economic interest for strawberry
Boudabous A., Jijakli H.,
For futher information
Biological control will help reduce the
ravages of grey mould suffered by the
strawberry trade (here in Tunisia).
Gaëlle Courcoux, coordinator
Délégation à l’information et à la communication
Tél. : +33 (0)4 91 99 94 90 - fax : +33 (0)4 91 99 92 28 - fichesactu@ird.fr