Effectiveness of native rhizobia for increased cowpea and groundnuts production in Uganda

Abstract

Cowpeas (Vigna unguiculata L.) and Groundnuts (Arachis hypogaea L.) production in Uganda is constrained greatly by low soil fertility, especially in dominant growing areas. Enhancing biological nitrogen fixation can greatly improve yields of these legumes. Therefore, native rhizobia were isolated from cowpea and groundnut nodules collected, which were used in the laboratory and screen house studies. The objectives were to i) determine the existence of native rhizobia strains in the dominant cowpea and groundnut growing areas of the eastern region of Uganda, ii) determine the efficacy of the isolated native rhizobia strains of cowpea and groundnuts for biological nitrogen fixation, and iii) determine nodule occupancy of native rhizobia strains for cowpea. The study obtained five native rhizobia isolates through molecular characterization which were grouped into three clusters. The screen house treatments for the groundnut crop were native isolates (GT24.1 and GT24.2), MAKbiofix (commercial inoculant) and non-inoculated control. For cowpea, the treatments included native isolates (CT34.3, CT40.3 and CB4.2), commercial strain Br3262 and a non-inoculated control. Inoculation with native rhizobia strain GT24.2 significantly increased the number of nodules, increased the concentration of plant tissue nitrogen and uptake in the groundnut. On the other hand, inoculation with the strain Br3262 and CT34.3 significantly increased the nitrogen uptake in the cowpea. It was further noted native isolate CT34.3 and CT40.3 were detected in 63% and 69% of nodules compared to 31% for Br3262 when these were inoculated on cowpea seed grown in non-sterilized soil. This indicated that the native strains CT34.3 and CT40.3 were more competitive than commercial strain BR3262 but will require further evaluation for their stability across different AEZ and agronomic management practices.