Options for Improving Plant Nutrition to Increase Common Bean Productivity in Africa

Common bean (Phaseolus vulgaris L.) is one of the most important grain legume crops in Africa. It represents an important share of food proteins and calories of poor agricultural populations in Eastern and Southern Africa. The production of bean in Africa is carried out primarily by small-scale farmers, who use little or no fertilizers or soil amendments. Average seed yields of beans in Africa are very low as compared to other production areas, mainly because of abiotic (edaphic and climatic) and biotic constraints. African soils are generally nutrient poor and application of adequate fertilizers is currently not feasible for economic and other reasons. The grain yield in the future can be increased by (i) using improved bean varieties that are better adapted to low soil fertility (ii) by application of fertilizers and managing soil fertility, and (iii) by optimizing the root symbioses to improve plant nutrient uptake under present conditions. Beans are forming two distinct types of symbiotic relations. They undergo nodulation with nitrogen-fixing bacteria and they also establish arbuscular mycorrhiza with Glomeromycota. Both of these symbioses affect in an important way the plant nutrient uptake. However, limited research efforts were made so far into studying the complex interactions between the three partners compared to the research focused either on biological nitrogen fixation or on mycorrhizal symbiosis. Thus the interactions among the symbiotic partners within the tripartite symbiosis are still poorly understood, though they might offer a potential to improve and sustain bean production in the tropics.