Fluorescent Pseudomonas spp., isolated from tomato and pepper plants rhizosphere soil,
was evaluated in vitro as a potential antagonist of fungal pathogens. Pseudomonas strains
were tested against the causal agents of tomatoes damping-off (Sclerotinia sclerotiorum),
root rot (Fusarium solani), and causal agents of stem canker and leaf blight (Alternaria
alternata). For this purpose, dual culture antagonism assays were carried out on 25% tryptic
soy agar, King B medium and potato dextrose agar to determine the effect of the strains on
mycelial growth of the pathogens. In addition, strains were screened for their ability to
produce exoenzymes and siderophores. All the strains significantly inhibited Alternaria
alternata, particularly in 25% TSA medium. Antagonistic effect on Sclerotinia sclerotiorum
and Fusarium solani was greater on King B medium. Protease was produced by 30% of the
strains, but no strain produced cellulase or chitinase. Finally, the selected Pseudomonas
strain, Psf5, was evaluated on tomato seedling development and as a potential candidate
for controlling tomato damping-off caused by Sclerotinia sclerotiorum, under growth
chamber conditions. In vivo studies resulted in significant increases in plant stand as well
as in root dry weight. Psf5 was able to establish and survive in tomato plants rhizosphere
after 40 days following the planting of bacterized seeds.
2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
* Corresponding author.
E-mail address: naceur.hamdi@isste.rnu.tn (N. Hamdi).
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