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SESSION 5: DISEASE CONTROL AND FORECASTING MODELS
P125 - The potential of biofungicides in controlling
soil born pathogen on tomato by inducing defense
response
W. Jendoubi 1 , R. Rodriguez 2 , W. Hamada 1
1 Laboratory of Genetics, National Agronomic Institute of Tunisia; 2 Sustainable Agro Solutions S.A,
Almacelles (Lleida), Spain
Email: w_hamada@yahoo.com
Some bio-fungicides were characterized for the mode of action and their
effectiveness in controlling soil born disease on tomato. Five natural products
containing seaweed, carbohydrates, phosphite, chitosan and the beneficial
bacterium Pseudomonas putida were compared to salicylic acid used as
reference as known to be involved in defense response pathway. Their indirect
mode of action was analyzed by application of the products on the plants before
challenging with the pathogen. The telluric fungus Fusarium oxysporum f. sp.
radicis Lycopersici (FORL) and the tomato crop were used as model of study.
Due to the difficulty of monitoring the efficacy of products in the amended soil, a
hydroponic system was adopted. After the application of either the tested or the
reference products, the effectiveness is evaluated based on the development of
disease symptoms on shoots and roots of the attacked plants. In order to
understand better the mode of action of these bio-fungicides in planta, analysis of
the release of the secondary metabolites specific of plant defense such as soluble
phenolics was undertaken and showed an accumulation of these compounds in
leaves of treated tomato plants. RT-PCR analysis of expression of the gene
encoding phenyl-amenia-lyase (PAL), encoding the synthesis of phytoalexin
representing parts of these compounds, confirmed the results found earlier.
Accordingly, the resistance observed in treated plants may be a direct result to
the accumulation of several phenolic compounds. Similarly peroxidase activity
has been assessed in leaves and roots of treated and inoculated tomato plants by
FORL. This analysis showed a remarkable increase of peroxidase activity in
treated and inoculated plants which is more significant in roots than in leaves. RT-
PCR analysis performed on the gene encoding peroxidase (PR9) confirmed the
results obtained following the peroxidase activity. Molecular analysis was also
undertaken in order to explain the mechanism that may be the basis of the type of
reaction observed. This analysis was based on monitoring the expression of three
genes encoding for three PR proteins namely PR2, PR4 and PR1and a gene that
lies upstream of all proteins PRs (NPR1). Follow up of the gene expression
showed accumulation of the PR proteins depending on the applied product. Thus,
we can conclude that part of the resistance observed may be explained by the
accumulation of transcripts of PR4, PR2 and PR1 after products application.
Keywords: biofungicides, plant defense activator, Fusarium
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