ESTABLISHMENT OF AN EFFECTIVE ENDOMYCORRHIZAL ASSOCIATION ON CASSAVA IN FLOWING SOLUTION CULTURE AND ITS EFFECTS ON PHOSPHORUS NUTRITION

Summary Eight cassava (Manihot esculenta) cultivars were grown with or without mycorrhizal inoculation in flowing solution cultures containing approximately 0.1, 1, 10 or 100 μM phosphate. Rice (Oryza sativa), maize (Zea mays), cowpea (Vigna unguiculata) and French bean (Phaseolus vulgaris) were included in the experiment for comparative purposes. Cassava required a higher external phosphorus concentration for maximum yield (≥ 10 μM) than the other species (≥ 1 μM) regardless of the inoculation treatments. Roots of inoculated cassava plants were heavily infected with VA endophytes at 0.1 and 1 μM phosphate, but not at 10 or 100 μM. Non-inoculated cassava plants were free of infection, and no infections were observed in any treatment on the other species. At 1 μM phosphate, infection of cassava roots was associated with large increases in whole plant dry wt, concentration of phosphorous in tops and roots, and total phosphorus uptake. At 0.1 μM phosphate there were also substantial increases in phosphorus concentration in tops and roots but the infected cassava plants were still severely phosphorus deficient and growth was not improved. The results are discussed in relation to the present state of knowledge about the phosphorus nutrition of cassava.