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English

Youssef Ismail

Étudiant Ph.D. de Mohamed Hijri

"Les interactions tripartites entre les plantes, les champignons pathogènes et des champignons mycorhiziens à arbuscules, en utilisant l’approche de la génomique fonctionnelle."

(Description disponible qu'en anglais)

Resistance, according to Agrios (1988) is the ability of an organism to exclude or overcome, completely or in some degree, the effect of a pathogen or other damaging factor. Disease resistance in plants is manifested by limited symptoms, reflecting the inability of the pathogen to grow or multiply and spread, and often takes the form of a hypersensitive reaction (HR), in which the pathogen remains confined to necrotic lesions near the site of infection. Induced resistance is the phenomenon that a plant, once appropriately stimulated, exhibits an enhanced resistance upon ‘challenge’ inoculation with a pathogen, although induced resistance has been attracting attention recently.

Induced or acquired resistance to disease in plants has been known for many years, but the phenomenon was studied in only a few laboratories until about a decade ago. Since then, there has been an increasing interest in induced resistance as a new, environmentally safe means of disease control, as well as a model for the study of the genes involved in host defense and the signals that control them. Plants can be induced locally and systemically to become more resistant to diseases through various biotic or abiotic stresses by various inducers. i) Chemical inducers such as application of exogenous salicylic acid and ethylene. ii) The biological inducers include necrotizing pathogens, non-pathogenic fungi, root colonizing bacteria and arbscular mycorrhizal fungi (AMF).

Some events similar to those found in plant-pathogen interactions have been also found in the plant interaction with AMF. These events include signal perception, signal transduction and defense gene activation. AMF secrete similar chitin elicitors, which could induce a defense response. There are several hypotheses about the mechanisms of the increased resistance in mycorrhizal plants: (1) improvement of plant nutrient status; (2) competition; (3) changed roots morphology and structure; (4) changed microbial flora in rhizosphere; (5) induced resistance or systematic resistance in plant. After colonized by AMF, phenolic compounds accumulate in plant, and local defense response or systemic defense response occurs. It is necessary to do intensive research on the mechanisms of increased resistance in mycorrhizal plants, because it may help us understand the function of disease resistance of mycorrhiza correctly, and let us use AMF as a new approach to control plant diseases in eco-agriculture in the near future. So, this study aims to:

Examine the ability of two different AMF (Glomus intraradices and G. mosseae) to induce resistance against diseases of potato plants caused by Phytophthora infestans, Verticillium dahliae and Rhizoctonia solani

1. Examine the involvement of the plant signal molecules (Jasmonic acid, ethylene and salicylic acid) in mycorrhizal plant and challenged by pathogens.

2. Examine the biochemical changes associated with local and systemic expression of defense-related genes such as,
   • Detection of chitinase and chitosanase activities
   • Detection of β-1,3-glucanase activity
   • Detection of Peroxidase activity
   • Detection of Super-oxide Dismutase activity
   • Detection of lytic activity mediated by AMF against fungal cell walls.

3. Quantitative PCR system for cloning and sequencing of resistance genes in response to inoculation with AMF and challenged by the pathogen for indicating the acquired resistance in both roots and leaves.