Résumé
In Sahelian zone, the low ecosystem productivity has been accelerated. This low production of ecosystems has been caused by anthropological activities and/or natural effects which, together result in deforestation and degradation of West African lands.lt has been demonstrated that fast-growing trees such as Australian species, able to grow in poor and disturbed soils, could promote rehabilitation on degraded topical lands.ln this way, Casuarina equisetifolia (Filao), a tree native to Australia was established in the Niayes region of Senegal in 1948. The symbiosis between Arbuscular Mycorrhiza Fungi (AMF) and Casuarina seedling improves the uptake of mineral nutrients such as phosphorus and nitrogen and enhances seedling development. With their nitrogen-fixing ability Casuarinas species increase the nitrogen availability in soils. In our work, we collected AMF strains from Australia SA (Casuarina's native zone) and from Senegal SS (introduced zone), evaluated their influence on C. equisetifolia growth and characterized the basis of their differences using molecular and histochemical markers of mycorrhizal symbiosis. C. equisetifolia plants were inoculated with Senegalese, Australian strains and/or with Frankia bacteria Ccl3. After 4 months in the greenhouse, plants were harvested; the biomass and mycorrhizal rate were assessed. Histological analysis was carried out on mycorrhizal roots using a new staining method, more rapid and less toxic than Trypan blue to assess the degree of AMF colonization. The expression of marker genes and the activity of mycorrhiza were analyzed using respectively molecular and histochemical techniques. The results show that this new staining method is an excellent technique to detect AMF in roots. Higher colonization and a positive C. equisetifolia development were obtained with plants inoculated with Senegalese fungus strains and this correlates with an increased expression of symbiotic marker genes and with an increased metabolic activity. These results allow the selection of effective mycosymbionts able to promote C. equisetifolia development and regenerate plantations of the Niayes region. (Résumé d'auteur)