Mycorrhizal associations: important for cassava grown on soils low in P

Cassava grows well on some low-P soils and is less responsive to P fertilizers than many other crops due to the association of cassava roots with certain soil fungi, called vesicular-arbuscular (VA) mycorrhiza. Aspects of the symbiotic relationship fungus/plant are described. VA mycorrhiza produce hyphae in and around the roots and form arbuscles and vesicles inside the root cortex. The P absorbed by the external hyphae of the fungus is released to the plant roots where interchange of substances occurs. More than 70 species have been identified, differing in their efficiency to absorb P. Since 1980 the Mycorrhiza Project at CIAT has collected, purified, and evaluated the efficiency of large no. of mycorrhizal strains to identify highly efficient strains adapted to particular soil and climatic conditions. Improved methods of inoculum production and application are also being studied. It is expected that the use of better strains will make field inoculation in nonsterilized soil an attractive alternative to using high levels of P fertilizer. (CIAT)