Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (http://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
http://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (http://www.sciepub.com)

Nodulation Potential of Bambara Groundnut (Vigna subterranea L.) in Yaounde (Centre Region of Cameroon)

Ndiang Zenabou*, Semboung Lang Firmin, Ngo Nkot Laurette, Wafo Fosso Daniel, Tchinda Ninla Laurianne, Bell Joseph Martin

Department of Botany, Faculty of Science, University of Douala, Po. Box. 24157, Cameroon

Abstract: Vigna subterranea (L.) Verdc., which is the third most important food legume in terms of production and consumption after peanuts (Arachis hypogeae L.) and cowpeas (Vigna unguiculata Walp.) with a very high nutritional value, remains a neglected and underutilized specie. Some morphotypes of Bambara groundnut were surveyed in order to constrain their nodulation potential six weeks after sowing. Nodules of fifteen plants per morphotype per replication were determined under pot experiment in non-sterile soil in Yaounde. The effectiveness of N-fixation was determined by measuring the above-ground plant size (PH) and biomass (SDW). All plants nodulated. Nodule number (NN = 11 - 108), nodule dry weight (NDW = 0.04-0.26 g), shoot height (SH = 20.48 - 30.96 cm), root length (RL = 34.6 - 52.1 cm), shoot dry weight (SDW = 2.45 - 7.08 g) and root dry weight (RDW = 0.34 - 1.28 g) vary from one morphotype to another. NN correlated positively and highly to the RDW (r = 0.75; p < 0.001) and NDW (r = 0.89; p < 0.001) revealing the root biomass as an indicator of good nodulation. SDW correlated positively and highly to the RDW (r = 0.70; p < 0.001) too, showing that the root biomass resulted from a good shoot system as NOR2Y morphotype. SDW shows positive and imperfect correlation with NDW (0.41) and NN (0.32) indicating that shoot biomass was not always the result of good nodulation. The nodulation potential of studied Bambara groundnut evidences their infectivity by indigenous rhizobacteria. It seems to be a good criterion for predicting high productive species and a selection marker for breeding programs.

Keywords: morphotypes, nodules, plant biomasses, Vigna subterranea

Received April 11, 2022; Revised May 16, 2022; Accepted May 26, 2022

Citation: Ndiang Zenabou, Semboung Lang Firmin, Ngo Nkot Laurette, Wafo Fosso Daniel, Tchinda Ninla Laurianne, Bell Joseph Martin, Nodulation Potential of Bambara Groundnut (Vigna subterranea L.) in Yaounde (Centre Region of Cameroon). American Journal of Food and Nutrition, 10 (1). 34-39. January 2022. doi:10.12691/ajfn-10-1-5

1. Introduction

The nitrogen (N) in soil represents one critical condition of plant growth in natural conditions as in crop production and breeding programs. It is considered as the most important component for supporting this plant growth capable of enhancing biomass accumulation [1]. As an essential macronutrient for plant function, N is a key component of amino acids building plant proteins and enzymes by helping to regulate water and nutrient uptake; and of chlorophyll molecules giving green colour to plants involving to create food for the plant through photosynthesis. Contrarily, lack of N can induce a chlorosis equivalent to the general yellowing of plants, smaller root systems and the reduction of food production. Moreover, N contributes in speedy shoot growth, flower differentiation, health of flower buds, increases the quality of fruit and acts as a catalyst for the other minerals [2]. This N is commonly available in soil without additional fertilizers. The trick is having healthy soil full of beneficial microorganisms such as Rhizobia that can make use of the N available in the air. Legumes through root nodules can fix N, boosting soil’s health. These root nodules are the salient feature of symbiosis with nitrogen-fixing soil bacteria [3]. Under conditions of low external input, the use of biological nitrogen fixation appears to be a cheaper and environmentally friendly source of N for plants [4].

Bambara groundnut (Vigna subterranea L. Verdc.) is a neglected and underutilized species (NUS) despite its promising richness of food resources. This plant could help to address nutritional problems and to attain food security through its high nutritional value and richness with its vitamin, micronutrient and protein contents. Furthermore, V. subterranea contributes to improving the natural resource base through addition of organic matter and biological nitrogen fixation [5]. It thrives well in nutrient poor soils due to its ability to form effective root nodules with compatible rhizobacteria.

Bambara groundnut morphotypes display several seed coat colours from black to mottled, and lighter cream pigmentation due largely to the presence of different types and concentrations of flavonoids [6]; it also fixes N under field and glasshouse conditions [7], reaching 42 - 62 kg ha⁻¹ in Ghana [8,9]. Because of the prohibitive cost of synthetic fertilizers for most African farmers, the identification of germplasm with highly efficient N fixing ability could provide an alternative cheap source of natural N benefiting for users and contribute to increase crop production. The present study aims to evaluate the nodulation potential of twelve Cameroonian Bambara groundnut morphotypes by identification and surveying promising genotypes for further development in breeding programs.

2. Materials and Methods

Table 1 presents characteristics of the soil sample (0-20 cm depth with a soil corer) collected from cropland at Eloumdeng II (N5°08’, E10°31’; 740 m) in the Yaounde suburb (Centre region of Cameroon) within the agro-ecological zone V. This soil sample was air-dried for two weeks, sieved to pass 5 mm and amount 100 g were collected for geochemical analysis. This agro-ecological zone V registers ~1836.7 mm/yr of rainfall, ~25.01°C of ambient temperature and ~75 % of humidity (Weather station of Yaounde, 2012).

Table 1. Soil chemical characteristics before the experiment

Seeds of twelve Bambara groundnut morphotypes (MBYO10, MBYO3, NOR1, NOR1Y, NOR2, NOR2Y, NOR4, NOR5, NOR6, NOR7, NOR8 and NOR9) of [10] and varying one to another by their growth habits and coat colours were used. The detailed description of these morphotypes is summarized in Table 2 with main characteristics of associated agro-ecological zones. Seeds were sterilized in 95 % ethanol during 5 mn, subsequently washed with distilled water and then pre-germinated on a wet filter paper for five days at 25°C. We planted two pre-germinated seeds per morphotype in pots of litres of volume and contained 2 kg soil. Fifteen replicate pots per morphotype were arranged randomly in the greenhouse. One week after planting, all pots were thinned to a plant per pot and watered daily to maintain the water-holding capacity of experimental soil.

Pot-grown plants were harvested at flowering, six weeks after sowing (WAS). From each plot, fifteen plants per morphotype were randomly taken and then separated into the shoot and root systems. Root nodules collected on roots were dehydrated in vials containing silica gel and stored at 4°C until use. The native bacteria infectivity was evaluated for their ability to induce nodule formation in B. groundnut roots. Selected nodules were prepared for nodule sectioning and visual observation. Nodulation efficiency is evidenced by observing the healthy, entirety and pink colour evidenced by the nitrogen fixing activity of nodules. We determined the number (NN) and dry weight (NDW) of viable nodules, separated and measured plant height (PH) and root length (RL). The effectiveness of N-fixation was determined by measuring the above-ground plant biomass, which was excised, dried at 70°C for 72 hours in an air oven and weighed (SDW) until constant weight. Both pot- and pouch-grown plants were harvested and weighed (RDW). Data collected were subjected to analysis of variance (ANOVA) using SPSS 23.0 and correlations between parameters of nodulation and growth were assessed. A p-value < 0.05 generally used to evaluate significance, although higher levels were considered for p-value < 0.001.

Table 2. Characteristics Bambara groundnut morphotypes [10] and harvested agro-ecological zones

3. Results

3.1. Infectivity and Efficiency of Indigenous Rhizobacteria

All roots of the twelve Bambara groundnut morphotypes display healthy and pink coloured nodules six week after sowing indicating the effective rhizobacteria infectivity known for their capability to induce such biological processes. Figure 1a present NN with an average ranges between 11-108 recorded from NOR2 and NOR4 respectively and p-value < 0.05. This nodule number per plant within morphotype defines three classes of morphotypes, < 40, [40-80] and > 80 equivalent to low, moderate and good nodulation potential. NOR2, NOR6 MBYO10, NOR5 and NOR1Y belong to class 1 with 11, 19, 23, 25 and 31 nodules per plant. NOR7, MBYO3 and NOR9 represent class 2 with 52, 57 and 62 nodules per plant. NOR1, NOR2Y and NOR4 represent class 3 and are the most productive with 84, 104 and 108 nodules per plant.

Figure 1. Nodulation potential a) Nodule number per plant b) Nodule dry weight

NDW (g) was significantly different (P < 0.05) among the morphotypes and ranges between 0.04-0.26 g in NOR2 and NOR2Y respectively for an average value of 0.11 (Figure 1b). NOR2, NOR5, NOR1Y, NOR6 and NOR9 have NDW lower than 0.1. Except NOR8 with NDW equals to 0.1, the NDW of NOR7, MBYO3, MBYO10, NOR1, NOR4 and NOR2Y were greater than 0.1. Except MBYO3 that displays a low number of nodules but a high weight, correlations between the NN and NDW are positive for all other morphotypes with highest nodule number corresponding to highest nodule dry weight and reversely.

NOR4 originated from North Cameroon is the most adapted with the highest nodule number than the local morphotypes MBYO3 and MBYO10. These also pinpoint preferential affinities between morphotypes regarding the native rhizobia strains and suggest the possible existence of a symbiotic link between introduced morphotypes with local rhizobia and the gene-for-gene relationship between the plant and the competent strains.

Given the importance of seed coat compounds in nodule formation, the variation in seed colour of Bambara groundnut probably plays a critical role in the choice of microsymbiont partner, attracting different types of native rhizobia with different levels of symbiotic efficiency.

3.2. Plant Growth and Biomasses of V. subterranea Morphotypes

Figure 2 presents the plant growth and biomasses, which vary from one morphotype to another, 6 WAS. The plant heights (PH) vary between 20.48 - 30.96 cm (Figure 2a). They form three classes of small, medium and large size plants. The first group with a lower size < 25 cm, is made up of NOR2, NOR6, NOR5, NOR1Y, NOR7, NOR8, NOR2Y and NOR4. Medium size plants range between 25 - 30 cm and comprise MBYO3, NOR9, NOR1. Only MBYO10 represent a large size with 30.96 cm.

Figure 2. Plant growth a) Plant height b) Root length

The root length (RL) i.e. vertical growth of the root varies from 34.6 - 52.1 cm and defines one class ([30 - 60] cm) at 6 WAS (Figure 2b). There was no significant difference for the rooting depth, i.e., taproot length between 30 - 60 cm. Morphotypes used in this study were originating from drier and wetter environments but soil nutrient and water acquisition are the same among them.

The shoot dry weight (SDW) varies between 2.45 - 7.08 g equivalent to NOR5 and MBYO10 respectively and defines three classes (Figure 3a). The first includes NOR5, NOR1, NOR6, N0R1Y, NOR7, NOR4 and NOR2 with SDW varying between 2.45 - 3.61 g. The second is made up of NOR8, NOR2Y, MBYO3, NOR9 with SDW ranging from 4.18 - 4.59 g. MBYO10 defines the third class with SDW greater than 7.00 g. The root dry weight (RDW) varies from 0.34-1.28 g (Figure 3b) and defines three classes (≤ 0.7; ]0.7 - 1] and >1). NOR1, MBYO3, NOR2, NOR1Y, NOR9, NOR2Y and NOR4 belong to the first class. MBYO10, NOR4, NOR6 and NOR8 form the second class while NOR7 alone defines the third class.

Figure 3. Plant biomasses a) Shoot dry weight b) Root dry weight

3.3. Correlation between Nodulation, Shoot and Root Biomasses

Table 3 shows the Spearman correlation coefficients (r) between nodulation, growth and development components. The positive and significant correlation recorded between the NN and RDW (r = 0.75; p ˂ 0.001) indicate that a plant which nodulated a lot had an abundant root system as NOR1, NOR4 and NOR2Y plants. Our findings highlight the positive and highly significant correlations between NN and NDW. Contrarily, the growth parameters RL and PH are not significantly correlated with the NDW and NN nodulation parameters. Highly significant correlation was found between SDW and RDW (r = 0.70; p ˂ 0.001), NN and NDW (r = 0.89; p ˂ 0.001) confirm its status as an indicator for efficiency in N fixation.

Positive and significant correlation between the bambara groundnut NN and plant biomasses (r = 0.80; P = 0.05) are found. The nodule regulation phenomenon cautions current results where the NN has any or limited influence on the growth of aerial and root systems (PH and RL). The positive and significant correlation between NN and RDW (r = 0.75; p ˂ 0.001) indicate that plant with the highest NN has an important root biomass. Reversely, RL and PH do not correlate significantly with NDW and NN. MBYO10 has a low NN with the highest shoot and root systems. The high correlation of RDW with most of the tested parameters confirm its reliability as an indicator for efficiency in N fixation.

Significant correlations were found between NDW and RDW (r = 0.74; p ˂ 0.001). The correlation between NDW and SDW was positive and imperfect (0.41; p < 0.05). These rhizobia would be efficient because of the positive effect of NDW on SDW and on the RDW. There would be very infectious strains in this soil but less efficiently and vise-versa, hence the results obtained with NOR1 which shows plants with a low SDW and high NN. Their correlation (0.32; p < 0.05) was positive and imperfect. Above morphotypes with highest nodulation potential and better root length seem to be appropriated for commercial production and further breeding programmes.

Table 3. Spearman Correlation coefficients among nodulation potential, plant growth and biomasses in V. subterranea

4. Discussion

4.1. Nodulation Potential

There was no history of inoculation at the soil sample used in this study. Then, the microsymbionts present in root nodules of twelve Bambara groundnut morphotypes were considered authentic indigenous occupants. Our findings show that all morphotypes nodulated (Figure 2). This demonstrates that the soil used for the experiment has indigenous rhizobacteria that were able to nodulate B. groundnut morphotypes as well as the efficient symbiotic relationships established between the two groups of organisms [11]. Similar findings for rhizobia collected from fields were found under mixed culture [12,13]. Three classes of NN indicate the overall N-fixation and nodulation potential of studied morphotypes and their dominant high to extremely very high nodulation potential. [14] mentioned the high nodulation potential of B. groundnuts in the Centre and Littoral regions of Cameroon. These variations of nodule numbers have been evocated on Phaseolus vulgaris [15] and Arachis hypogaea [13].

Except MBYO3 that displays a low number of nodules but a high weight, correlations between the NN and NDW are positive for all other morphotypes with highest nodule number corresponding to highest nodule dry weight and reversely. The highest nodule dry weight observed in MBYO10 pinpoints their biggest sizes and heaviest characters than those of other morphotypes. This indicates that both characters do not match systematically. The nodule dry weight inferred to its size could reveal other symbiotic inputs. [16] reported that nodule dry weight as a revelatory feature of the symbiotic relationship between root nodule bacteria and legumes. E.g.: [17] showed that nodulation and nitrogen fixing activity of several species of legumes vary according to the origin or the genotype of the host plant. The genotype of the plant can also influence nodulation and nitrogen fixation in peanuts [18]. NOR4 originated from North Cameroon is the most adapted with the highest nodule number than the local morphotypes MBYO3 and MBYO10. These also pinpoint preferential affinities between morphotypes regarding the native rhizobia strains and suggest the possible existence of a symbiotic link between introduced morphotypes with local rhizobia and the gene-for-gene relationship between the plant and the competent strains. Like the microbial partner, the host plant could also influence the effectiveness of the legume-rhizobia symbiosis [19]. Given the importance of seed coat compounds in nodule formation, the variation in seed colour of Bambara groundnut probably plays a critical role in the choice of microsymbiont partner, attracting different types of native rhizobia with different levels of symbiotic efficiency. These seed coat flavonoids seem to serve as signal molecules for compatible soil rhizobia during nodule formation [20]. Therefore, they influence bacterial partner specific choice.

4.2. Practical Implications and Perspectives

This study evaluated the nodulation potential of Bambara groundnut morphotypes. This nodulation potential seems to be associated with plant growth and biomass. Both are to the shoot and rout lengths and nodulation. For the plant growth, only MBYO10 that represents a large size (˃30 cm) while all others are lower < 25 cm (NOR2, NOR6, NOR5, NOR1Y, NOR7, NOR8, NOR2Y and NOR4) and medium 25 - 30 cm (MBYO3, NOR9, NOR1) size plants (Figure 2a). The root length (RL) i.e. vertical growth that defined one classe ([30 - 60] cm) at 6 WAS (Figure 2b), was not significant for the rooting depth. The taproot length (30-60 cm) in our B. groundnut morphotypes belong to the latest class of [21] in deeper soil depths at 35 days after sowing. Any specifically studied Bambara groundnut genotype represents its greater to greatest root length distribution (60 to 90 cm). This also indicates the availability of water resources at superficial soil levels.

NOR2Y, NOR4 and MBYO10 are morphotypes that also have better root length and root dry weight potentials to uptake nutrients and water mainly in the studied area producing many mature pods [22]. MBYO10 produced more aboveground biomass and NOR2Y produced more belowground biomass showing their best shoot and root characteristics, respectively. [23] documented that the highest root volume in species likely explore the rhizosphere more intensively for nutrients, water and mycorrhizal associations, able to mat and bind soil particles together, reducing rill and interrill erosion on cultivated plots.

NN and NDW correlate positively and are highly significant correlations. Contrarily, the growth parameters RL and PH are not significantly correlated with the NDW and NN nodulation parameters. [24,25] established different correlations between NN or NDW and the increasing dry weight of the aerial parts. The highly significant correlation between SDW and RDW (r = 0.70; p < 0.001), NN and NDW (r = 0.89; p < 0.001) confirm their status as indicators for efficiency in N fixation as documented in common bean by [26]. [27] described a similar positive and significant correlation between the bambara groundnut NN and plant biomasses (r = 0.80; P = 0.05). Our findings do not corroborate with those of [25] who found a negative correlation between NN and NDW in chickpeas inoculated with different strains of rhizobia. The nodule regulation phenomenon cautions current results where the NN has any or limited influence on the growth of aerial and root systems (PH and RL) such as MBYO10 that has a low NN with the highest shoot and root systems. [14] showed that the quality of soil used to influence the RDW and NN in B. groundnut. The high correlation of RDW with most of the tested parameters confirm its reliability as an indicator for efficiency in N fixation. [25] concluded that these positive and perfect correlations indicate the dual evolution between concerned parameters and highlighted the significant difference in the effect of strains on bean root growth. These rhizobia would be efficient because of the positive effect of NDW on SDW and on the RDW. There would be very infectious strains in this soil but less efficiently and vice-versa, hence the results obtained with NOR1 which shows plants with a low SDW and high NN.

Our results reveal three types of B. groundnut morphotypes with low, moderate and good nodulation potential. Those with highest nodulation potential and better root length seem to be appropriated for commercial production. The nodulation potential can be considered as a selection marker in further breeding programmes.

5. Conclusion

Twelve selected local Bambara groundnut morphotypes were surveyed in order to constrain their nodulation potentials and plant growth in non-sterile soil from the Centre region in Cameroon. The results show that the soil has indigenous rhizobia allowing B. groundnut genotypes to nodulate at 6 weeks after sowing indicating their high symbiotic N₂ fixation. NOR1 shows lowest SDW and high NN contrarily for MBYO3 and MBYO10 that have highest SDW and lowest NN. Morphotypes with the highest NN coincide with those having the highest NDW except for MBYO3 and MBYO10 which have lowest NN and the highest NDW, related dominantly to nodule size than number expressing genotypic and even nutritional specificities. MBYO3 and MBYO10 morphotypes with the highest shoot biomass, NN and NDW seem to be the most producing usable for varietal improvement programs. The nodulation potential of V. subterranea can be used as a selection marker in breeding programs.

Acknowledgements

The authors are thankful to Dr Koji Ernest for their statistical analysis.

Competing Interests

The authors have no competing interests.

References

[1]  
Nadeem, F., Ahmad, Z., Wang, R., Han, J., Shen, Q., Chang, F., Diao, X., Zhang, F., and Li, X. Foxtail Millet [Setaria italica (L.) Beauv.] Grown under Low Nitrogen Shows a Smaller Root System, Enhanced Biomass Accumulation, and Nitrate Transporter Expression. Front plant Science, 9(205), 1-12, 2018.

[2]   | Leghari, S. J., Wahocho, N. A., Laghari, G. M., Laghari, A. H., Bhabhan, G., M., Talpur, K., H., Safdar, T., A., Wahocho, S. A. and Leghari, A. A. “Role of nitrogen for plant growth and development: a review.” Advances in Environmental Biology, 10(9), 209-218, 2016.
[3]   | Szczyglowski, K. and Ross, L. Baring the roots of nodulation. Nature Plants, 7, 244-245, 2021.
[4]   | Peoples, M. B., Herridge, D. F. and Ladha, J. K. Biological nitrogen fixation: an efficient source of nitrogen for sustainable agricultural production. Plant and Soil, 174, 3-28, 1995.
[5]   | Kindeya, Y. B., Girmay, D., Atsbiha, A., Abadi, A., Negash, W., Gebregergies, G. and Gebremedhn, Z. Morphological characterization and evaluation of mungbean (Vigna radiata (L) Wilczek) genotypes in Western Tigray, Ethiopia. Journal of Experimental Agriculture International, 42(9), 25-37, 2020.
[6]   | Ndakidemi, P. A. and Dakora, F. D. Legume seed flavonoids and nitrogenous metabolites as signals and protectants in early seedling development. Functional Plant Biology 30, 729-745, 2003.

[7]  
Mohale, K. C., Belane, A. K. and Dakora, F. D. Symbiotic N nutrition, C assimilation, and plant water use efficiency in Bambara groundnut (Vigna subterranea L. Verdc) grown in farmers' fields in South Africa, measured using 15N and 13C natural abundance. Biology and Fertility of Soils, 50, 307-319, 2013.

[8]   | Peoples, M. B. and Herridge D. F. Nitrogen fixation by legumes in tropical and subtropical agriculture. Advances in Agronomy, 44, 155-223, 1990.
[9]   | Peoples MB, Herridge DF, Ladha JK. 1995. Biological nitrogen fixation: an efficient source of nitrogen for sustainable agricultural production. Plant Soil, 174: 3-28.
[10]   | Ndiang, Z., Bell, J. M., Ouattara, B., Mokake, S. E., Ngalle, H. B. and Fonceka, D. Variation in Seeds Physical Traits of Bambara Groundnut (Vigna subterranea) Collected in Cameroon. American Journal of Experimental Agriculture, 12(2), 1-8, 2016.
[11]   | Rogel, M. A., Ormeño-Orrillo, E. and Romero, E. M. Symbiovars in rhizobia reflect bacterial adaptation to legumes. Systematic and Applied Microbiology, 34(2), 96-104, 2011.
[12]   | Egbe O.M., Godwin Adu Alhassan G.A. & Ijoyah M. (2013). Nodulation, nitrogen yield and fixation by Bambara groundnut (Vigna Subterranea (L.)Verdc.) landraces intercropped with cowpea and maize in southern guinea savanna of Nigeria. Agricultural Science, 1: 15-28.
[13]   | Ngo Nkot, L., Nwaga, D., Ngakou, A., Fankem, H. and Etoa, F. X. Variation in nodulation and growth of groundnut (Arachis hypogaea L.) on oxisols from land use systems of the humid forest zone in southern Cameroon. African Journal of Biotechnology; 10(20), 3996-4004, 2011.

[14]  
Ngo Nkot, L., Ngo Bisseck, M., Fankem, H., Adamou, S., Kamguia, K., Ngakou, A., Nwaga, D. and Etoa, F. X. “Isolation and Screening of Indigenous Bambara Groundnut (Vigna Subterranea) Nodulating Bacteria for their Tolerance to Some Environmental Stresses.” American Journal of Microbiological Research, 3(2), 65-75, 2015.

[15]   | Amijee, F. and Giller, K. E. Environmental constraints to nodulation and nitrogen fixation of Phaseolus vulgaris (L.) in Tanzania. I. A survey of soil fertility, root nodulation and multilocational responses to Rhizobium inoculation. African Crop Science Journal, 6, 159-169, 1998.
[16]   | O’Hara, G. W. The role of nitrogen fixation in crop production. Journal of Crop Production, 1, 115-138, 1998.
[17]   | Perret, X., Staehelin, C. and Broughton, W. J. Molecular basis of symbiotic promiscuity. Microbiology and Molecular Biology Reviews, 64, 180-201, 2000.
[18]   | Alkama, N. Adaptation de la symbiose rhizobienne chez le haricot à la déficience en phosphore : détermination de la réponse de la plante en terme d’échanges gazeux et de flux minéraux échangés avec la rhizosphère. [PhD thesis], ENSAA of Alger (Algeria) and SupAgro of Montpellier (France), 2010.
[19]   | Aguilar, J. M. M., Ashby, A. M., Richards, A. J. M., Loake, G. J., Watson, M. D. and Shaw, C. H. Chemotaxis of Rhizobium leguminosarum biovar phaseoli towards flavonoid inducers of the symbiotic nodulation genes. Journal of General Microbiology, 134, 2741-2746, 1988.
[20]   | Subramanian, S., Stacey, G. and Yu, O. Distinct, crucial roles of flavonoids during legume nodulation. Trends in Plant Science, 12, 282-285, 2007.
[21]   | Mateva, K. I., Chai, H. H., Mayes, S. and Massawe, F. Root Foraging Capacity in Bambara Groundnut (Vigna Subterranea (L.) Verdc.) Core Parental Lines Depends on the Root System Architecture during the Pre-Flowering Stage. Plants. 9 (645), 1-22, 2020.
[22]   | Ndiang, Z., Bell, J. M., Fokam, P. E., Ouattara, B, Simo, C. and Dibong, D. S. Agro-morphological variability in twelve bambara groundnut (Vigna subterranea (L.) Verdc.) accessions in Cameroon. Sciences, Technologies et Développement, 16, 38-45, 2014.
[23]   | Anikwe, M. and Atuma, J. Characterizing the suitability of selected indigenous soil improving legumes in a humid tropical environment using shoot and root attributes. Tropicultura, 21 (4), 179-185, 2003.
[24]   | Depret G. and Laguerre, G. Plant phenology and genetic variability in root and nodule development strongly influence genetic structuring of Rhizobium leguminosarum biovar viciae populations nodulating pea. New Phytologist, 179, 224-235, 2008.
[25]   | Laguerre, G., Depret, G., Bourion, V. and Duc, G. Rhizobium leguminosarum bv. Viciae genotypes interact with pea plants in developmental responses of nodules, roots and shoots. New Phytologist, 176, 680-690, 2007.

[26]  
Kawaka, F., Dida, M. M., Opala, P. A., Ombori, O., Maingi, J., Osoro, N., Muthini, M., Amoding, A., Mukaminega, D. and Muoma, J. Symbiotic Efficiency of Native Rhizobia Nodulating Common Bean (Phaseolus vulgaris L.) in Soils of Western Kenya. International Scholarly Research Notices, Article ID 258497, 2014.

[27]   | Ngakou, A., Megueni, C., Ousseni, H. and Massai, A. Study on the isolation and characterization of rhizobia strains as biofertilizer tools for growth improvement of four-grain legumes in Ngaoundéré-Cameroon. International Journal of Biological and Chemical Sciences, 3(5), 1078-1089, 2009.