Date Published: August 01, 2017
Author(s): Amaral Machaculeha Chibeba, Stephen Kyei-Boahen, Maria de Fátima Guimarães, Marco Antonio Nogueira, Mariangela Hungria.
•Biological nitrogen fixation (BNF) is a key process for soybean production in Africa.•The selection of elite African indigenous soybean Bradyrhizobium strains is a feasible strategy.•Eighty-seven isolates were obtained from soybean nodules in Mozambique.•Isolates fit into the Bradyrhizobium (75%) and Agrobacterium-Rhizobium (25%) clades.•Five Bradyrhizobium isolates with outstanding symbiotic performance were obtained.
Soybean [Glycine max (Linnaeus) Merrill] stands out as the best-bet legume to feed the growing world population, projected to be between 9.6 and 12.3 billion in 2100, with much of the increase expected to happen in Africa (Gerland et al., 2014, UN, 2015). With approximately 40% seed protein and 20% seed oil content (Arslanoglu et al., 2011), soybean is an excellent source of food, fodder and biofuels. Like most legumes, soybean has the ability to reduce atmospheric nitrogen (N2) to a biologically usable ammonia (NH3), in association with bacteria collectively known as rhizobia (Singleton et al., 1992, Giller, 2001), obviating the need for N fertilizers. This is particularly important in Africa, where the predominantly subsistence farmers can hardly afford the limited available agricultural inputs (Singleton et al., 1992, Maingi et al., 2006, Chianu et al., 2011). In Mozambique, the demand for soybean has increased notably in recent years (Lava Kumar et al., 2011, Cunguara et al., 2012), to supply the growing poultry industry and for exportation (Dias and Amane, 2011, Muananamuale et al., 2012).
A total of 87 indigenous isolates trapped by promiscuous soybean cultivars (TGx) from soils of Mozambique were studied. The isolates were assigned to the Bradyrhizobium (75%) and Agrobacterium/Rhizobium (25%) genera. Most (63%) of the Bradyrhizobium isolates clustered within the superclade B. elkanii and the remaining showed genetic relatedness to the superclade B. japonicum. Bradyrhizobium has been repeatedly reported among indigenous rhizobia in Africa. In a study conducted in Malawi, B. elkanii was the dominant species that formed nodules with soybean (Parr, 2014). A survey conducted in Kenya identified all indigenous rhizobia nodulating soybean as B. elkanii (Herrmann et al., 2014). In addition, a study conducted with indigenous rhizobia isolated from soybean in Benin, Cameroon, Ghana, Nigeria, Togo and Uganda revealed the genera Bradyrhizobium and Rhizobium as the most abundant, and B. elkanii and B. japonicum were the most common species identified (Abaidoo et al., 2000).