Rhizosphere Microbial Community Structure of Promiscuous Soybean Cultivars in the Guinea Savanna Zone of Ghana.

The rhizosphere microbial community composition and activity are affected by soil properties, management practices, plant species or varieties, and growth stages. To gain a better insight into how crop cultivars and growth are affected by the rhizosphere microbial communities, a field study was conducted in 2016 at Nyankpala in Northern Ghana. The objective of the study was to determine whether different promiscuous soybean cultivars select for specific microbes at different growth stages, and how this impacts soil quality, nodulation, and yield. The experiment was laid-out as a split plot design, where the main plot factor consisted of three TGX (Tropical Glycine max crosses) cultivars: Jenguma (TGX1448-2E), Afayak (TGX1834-5E), and Songda (TGX 1445-3E). The subplot factor consisted of three types of commercial Bradyhizobium inoculants: Legumefix (USDA 532c strain), Biofix (USDA 110 strain), and Nodumax (USDA 110 strain), and control. Rhizosphere soil was randomly sampled from 10 soybean plants at various growth stages; 33 (V8, 8 leaf), 53 (R2, flowering), 90 (R4, podding) and 110 (R6, seeding) days after sowing (DAS) respectively. Analyses included phospholipid fatty acid (PLFA), soil pH, and N (NO₃-N and NH₄-N), nodulation and yield. Total PLFA (microbial biomass), gram-negative bacteria and arbuscular mycorrhizal fungi (AMF) abundances increased with growth stages. Rhizosphere N significantly increased due to the interaction effect of inoculant and growth stage. The interaction effect of cultivar and growth stage resulted in rhizosphere pH decline. Shoot biomass and side root nodulation were affected by the interactive effect of cultivar and inoculation. Inoculating Afayak with Biofix and Legumefix, and Jenguma with all inoculant types (Biofix, Legumefix, and Nodumax) increased side root nodulation. Inoculation with Biofix and Nodumax increased grain yield compared to the control. In conclusion, inoculation enhanced nodulation, biomass production, and grain yield (~ 30%) in promiscuous soybean cultivars.