TITLE:
Morpho-Cultural Characterization, Physicochemical Activities, and Effect of Abiotic Factors on the Growth of Rhizobium sp. Isolated from Nodules of 18 Soybean (Glycine max (L.) Merr.) Varieties Farmed in Cameroon
AUTHORS:
Linda Manet, Hippolyte Mouafo Tene, Eddy Léonard Ngonkeu Mangaptche, Onana Boyomo, Ferdinand Lanvin Edoun Ebouel, Gabriel Medoua Nama, Aimé Didier Begoudé Boyogueno
KEYWORDS:
Soybean, Nodules, Rhizobium sp., Adaptation, Abiotic Stress, Physicochemical Activity
JOURNAL NAME:
Open Journal of Soil Science,
Vol.15 No.6,
June
24,
2025
ABSTRACT: Acidic pH, high salinities, and extreme temperatures limit agricultural production in tropical soils, particularly in Cameroon. Rhizobia can improve crop growth and productivity in these soils, thanks to their ability to adapt to stressful conditions. In this study, nodules of 18 varieties of soybeans (Glycine max (L.) Merr.) were used to isolate rhizobia. The isolates were characterized and screened for their resistance to pH (2 to 6.8), salinity (NaCl 2% to 12%, w/v), and temperature (15˚C to 45˚C). Then, the physicochemical activity (catalase, proteins, total antioxidant capacity (TAC), ferrous reducing antioxidant power (FRAP), and malondialdehyde (MDA) of the isolates was assessed using referenced methods. The results showed that out of 108 isolates obtained, 73 were Rhizobium sp., endowed with variable pH, salinity, and temperature adaptabilities. The highest acid resistance (pH 2 to 4), salinity (4% to 12%), and extreme temperature (40˚C to 45˚C) were recorded with isolates 1M, 2M, 7M, and 5M. Isolate 10G2 showed the highest protein content (135.33 ± 5.65 µg/mL), while the isolates 1, 2G, 5P', and 13M scored the highest catalase activity (0.07 ± 0.00 µmol/mL/g prot). All the isolates demonstrated antioxidant activity, with the highest FRAP recorded by isolate 7M (298.46 ± 0.00 µg AAE/mL) and the highest TAC by isolate 4M1 (1335.93 ± 10.84 µg AAE/mL). They also presented the ability to inhibit oxidative stress through the inhibition of MDA production. The lowest MDA value (1.14 ± 0.05 µmol/L) was obtained with the isolate 11G3. Generally, the isolates with interesting adaptation to abiotic conditions and physicochemical activities were from soybean varieties TGX 2007-11 F, TGX 2001-12 F, TGX 1991-22 F, SC Sentinel, Panorama 3, Maksoy 2N, Panorama 237, and Panorama 2. These results highlight the potential of Rhizobium sp. isolated from soybean nodules in improving the crop productivity of tropical soils and suggest further characterization of these strains using genomic approaches.