Diversity of wild herbaceous legumes in southern Africa, their associated root nodule bacteria, and insect pests.

Abstract

Climate change models predict that most parts of southern Africa including Botswana and Namibia will experience severe water stress and temperature increases as a result of climate change. Wild drought-tolerant nitrogen-fixing plants with heat-tolerant bacterial symbionts might be a source for mitigation, nutrient-rich grazing grounds, and soil fertility. Herbaceous legumes may be developed into forage plants that are resilient to climate change effects. Therefore, the purpose of the study was to assess the diversity of wild herbaceous legumes in the north-western and eastern parts of Botswana, northern parts of Namibia, and Northern Cape of South Africa. They were assessed for nodulation and insect damage, root nodule bacteria were isolated, and some were identified and authenticated on their homologous hosts. In Namibia, rhizosphere bacteria were isolated and characterised. For the first time, it was shown that a wide range of wild legumes in the study area were nodulated. Common plant species included, amongst others, Chamaecrista bieinsis (Stey.) Lock, Chamaecrista absus (L.) Irwin and Barneby, Zornia glochidata DC, and several Crotalaria and Indigofera species. The jewel beetle Sphenoptera sp. damaged over 90% of the Indigofera sp. in Lecheng. The bacteria isolated were typical plant growth-promoting bacteria mostly belonging to the Bacillus and Brevibacillus genera, with fewer rhizobial species. Such bacteria may be valuable inoculants for pulses and cereals, respectively. Taken together, the results of this study highlight the potential for herbaceous legumes in mitigating climate change effects through the use of inoculants as biofertiliser and through use in intercropping that modulates pest infestation, leading to low usage of chemical pesticides.