Arbuscular mycorrhizae in Malagasy cropping systems

In Madagascar, rice production is low (2 t ha(-1)) and does not cover the needs of the population. To satisfy the food requirements, there is a need to develop agriculture on highland areas called "tanety". Soils of tanety have low nutrients availability, particularly phosphorus which is the main plant growth limiting factor (soil solution < 0.1 mg P l(-1)). Arbuscular mycorrhizal (AM) symbiosis is widely recognized to have high significance for tropical agriculture, particularly for plant P nutrition. The mycorrhizal status of some wild and cultivated plants was determined. Roots were sampled in two locations: the highlands and in the cliff-east. AM development (internal vesicles and hyphae) was estimated by microscopic examination. For the first time several native plants from Madagascar were reported as forming arbuscular mycorrhizae. Crop plants from the highlands were less colonized by AM fungi than wild species, whereas cultivated and wild plants from fallows areas were highly colonized by AM fungi. In highlands, for a long time, dry plants were burnt in furrows to release mineral nutrients. This practice is suspected to have decreased AM fungi population. Four AM fungi were isolated from colonized roots. Two of them were identified as G. fasciculatum. They were successfully propagated on leek growing on red pouzzolane. The efficiency of these isolates was tested in comparison with a strain of Glomus intraradices and found to be more efficient.