Arbuscular Mycorrhizal Inoculation of Peanut in Low-Fertile Tropical Soil. II. Alleviation of Drought Stress

The effect of drought stress and inoculation with an indigenous Mozambican and a commercial arbuscular mycorrhizal (AM) inoculant on root colonization and plant growth and yield was studied in two peanut (Arachis hypogaea L.) cultivars—a traditional, low-yielding Mozambican landrace (Local) and a modern, high-yielding cultivar (Falcon)—grown in a non-sterile Mozambican soil. In these cultivars, AM mycorrhizal colonization was not substantially reduced by drought stress. Growth and yield of inoculated plants subjected to drought stress were increased in comparison with non-inoculated ones. The indigenous Mozambique inoculant significantly increased leaf and root growth in both cultivars under drought stress by preventing an increase in root weight ratio (RWR) and maximum root-length to leaf-area ratio (MRLAR). The commercial Hannover inoculant had a positive effect on growth only under well-watered conditions, this result was due most likely to a lesser ability to adapt to drought conditions to which the AM fungal strains in Mozambique inoculant are frequently exposed. Such drought-stress effects on growth could be alleviated by inoculation with Mozambique inoculant, particularly because of its ability to decrease sensitivity of the host plant to reduction in leaf expansion. Therefore, an adequate management of the AM symbiosis may improve peanut productivity, particularly under drought stress and in small-scale farming systems.