Senegalia Senegal (Synonym: Acacia Senegal), Its Importance to Sub-Saharan Africa, and Its Relationship with a Wide Range of Symbiotic Soil Microorganisms
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UCLA UCLA Previously Published Works Title Senegalia senegal (synonym: Acacia senegal), its importance to sub-Saharan Africa, and its relationship with a wide range of symbiotic soil microorganisms Permalink https://escholarship.org/uc/item/7ss3w8qj Authors Bakhoum, N A.M. Hirsch D. Balachandar et al. Publication Date 2018-11-01 DOI 10.1016/j.sajb.2018.10.007 Peer reviewed eScholarship.org Powered by the California Digital Library University of California South African Journal of Botany 119 (2018) 362–368 Contents lists available at ScienceDirect South African Journal of Botany journal homepage: www.elsevier.com/locate/sajb Review Senegalia senegal (synonym: Acacia senegal), its importance to sub-Saharan Africa, and its relationship with a wide range of symbiotic soil microorganisms N. Bakhoum a,b,c,D.Falla,b,d,F.Falla,b,F.Dioufa,b,A.M.Hirsche,⁎,D.Balachandarf,D.Dioufa,b,c a LCM-Laboratoire Commun de Microbiologie IRD/ISRA/UCAD, Centre de Recherche de Bel-Air, BP 1386 Dakar, Sénégal b Laboratoire Mixte International Adaptation des Plantes et microorganismes associés aux Stress Environnementaux (LAPSE), BP 1386 Dakar, Sénégal c Département de Biologie Végétale, Université Cheikh Anta Diop de Dakar, BP 5005 Dakar, Sénégal d ISRA/CNRF, Route des Pères Maristes, BP 2312 Dakar, Sénégal e Molecular, Cell & Developmental Biology and Molecular Biology Institute, UCLA, 621 Charles Young Drive South, Los Angeles, CA 90095-1606, USA f Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore 641 003, India article info abstract Article history: Changing environmental conditions in dryland areas exacerbate land degradation and food insecurity in many Received 9 June 2018 sub-Saharan African nations. Multi-purpose tree species such as Senegalia senegal (L.) Britton, are favored for refor- Received in revised form 14 August 2018 estation and land reclamation as compared to single-use species. A great deal of research has also focused on this Accepted 3 October 2018 tree species due to its ability to fix atmospheric nitrogen into ammonia, which is returned over time to the soil via Available online xxxx the recycling of N-rich plant tissue. We review the recent literature on how S. senegal contributes to soil fertility Edited by B-E Van Wyk andcropproductionespeciallyinthecontextofsustainable and ecological agriculture. We also review the current literature on this legume species with regard to its microsymbionts, with the goal of further maximizing the poten- Keywords: tial of S. senegal for agriculture in sub-Saharan Africa. Senegalia senegal, which has the potential to restore degraded Acacia soils and to be used for agroforestry, is both economically and ecologically important for the dry areas of sub-Sa- S. senegal haran Africa because it produces gum arabic, an important commodity crop for smallholder farmers; it succeeds Symbiosis where other crops fail. This tree species also can correct soil fertility loss caused by continuous agriculture and Soil fertility worsened by a reduced or non-existent fallow period. Senegalia senegal and its soil microbes are positively associ- Microsymbionts ated with this species' ability to survive in harsh conditions. This tree is an important candidate for restoring soil Diversity fertility and providing commercial products especially in countries with arid environments. Soil salinity © 2018 SAAB. Published by Elsevier B.V. All rights reserved. Contents 1. Introduction.............................................................. 363 2. Diversity within S. senegal trees...................................................... 363 3. Senegalia senegal gumproduction..................................................... 364 4. Microsymbionts associated with S. senegal ................................................. 364 5. Inoculation of S. senegal withrhizobia................................................... 364 6. Inoculation of S. senegal withmycorrhiza................................................. 365 7. Effect of S. senegal onsoilfertility..................................................... 365 8. Use of S. senegal toaddresssoilaffectedbysalinity............................................. 366 9. Conclusion............................................................... 366 Acknowledgments.............................................................. 366 References.................................................................. 366 ⁎ Corresponding author at: Department of Molecular, Cell & Developmental Biology and Molecular Biology Institute, UCLA, 621 Charles Young Drive South, Los Angeles, CA 90095-1606, USA. E-mail address: [email protected] (A.M. Hirsch). https://doi.org/10.1016/j.sajb.2018.10.007 0254-6299/© 2018 SAAB. Published by Elsevier B.V. All rights reserved. N. Bakhoum et al. / South African Journal of Botany 119 (2018) 362–368 363 1. Introduction their host plants that improve both water and nutrient uptake. They also protect their hosts against plant pathogens (Smith and Read, Acacia (mimosoid clade; (LPWG, 2017)) shrubs and trees are com- 2008). Although S. senegal plays both economic and ecological roles mon in the savannas and drylands of Africa, Australia, India, and South and is used for agroforestry, information regarding the species is and North America and are frequently planted in the Sahel region of scattered and up to now, very little data integration has taken place. Africa (Dreyfus and Dommergues, 1981). The genus name Acacia was Our objectives in this review are to: (1) highlight the diversity recently changed for the African species because of their polyphyletic within S. senegal; (2) assess the chemical quality and factors influencing nature. They are found not only in Africa, but also in Central and South gum arabic; (3) describe the microsymbionts associated with S. senegal America, and Asia and comprise more than 60 species. Kyalangalilwa and the impact of their inoculation on the plant and the rhizosphere; et al. (2013) separated Acacia sensu lato into two new genera, namely and (4) lastly, summarize the effects of S. senegal on soil fertility and rec- Senegalia and Vachellia. Senegalia senegal is now the accepted name of lamation of soil damaged by salinity. what was formerly called Acacia senegal. Senegalia senegal is a multipurpose agroforestry tree species (Raddad and Luukkanen, 2007), and this small tree or shrub species 2. Diversity within S. senegal trees (Fig. 1) is one of the most commercially exploited (Fagg and Allison, 2004). This legume produces gum arabic, which is used for foods, bever- Senegalia senegal can be divided into four different varieties based on ages, pharmaceuticals, and cosmetics, and other applications. Senegalia morphology: senegal, kerensis, rostrata, and leiorhachis (Fagg and senegal also supports dryland ecosystems in tropical Africa (Fagg and Allison, 2004). The variety senegal is established in West Africa and Allison, 2004; Gray et al., 2013; Odee et al., 2011; Omondi et al., 2010; also East Africa, as are the leiorhachis and kerensis varieties (Fig. 2). Sprent et al., 2010). Agroforestry systems based on S. senegal and a vari- Previously range-wide genetic studies of S. senegal revealed differ- ety of crops produce combined yields that are larger than when the ences among varieties and provenances, especially between West Africa trees or agricultural crops are grown separately. It accumulates a large and eastern and southern Africa (Chevallier and Borgel, 1998; Odee et biomass when given sufficient water (Gaafar et al., 2006). In Sudan, a al., 2012, 2015). For example, the variety senegal exhibits a different traditional rotation with agricultural crops and S. senegal was shown population structure in Senegal (Chevallier et al., 1994). Isoenzyme to maintain soil fertility (Ballal et al., 2005; Barbier, 1992) and has a electrophoresis demonstrated low genetic variability in S. senegal var. low input production cycle (Raddad et al., 2006). Despite S. senegal's senegal populations, which indicated that the differences between prov- commercial, industrial, agricultural, and ecological importance, this enances were low although rare alleles were sometimes observed (Sall, tree still remains under-utilized in African drylands. This under-utiliza- 1997). In contrast, Omondi et al. (2010) observed a high genetic diver- tion is attributed to a lack of knowledge of production systems and also sity and low inter-population genetic differentiation in the kerensis to the fact that there are relatively few seed sources (Omondi et al., variety in Kenya. In a large S. senegal genetic diversity study that used 2010). Nonetheless, S. senegal has been a successful crop in agroforestry ITS and chloroplast DNA (cpDNA) analysis, Odee et al. (2012) observed systems in the Sudan and several West African nations (Anderson, genetic variation based on geography, such that the eastern and south- 1988). ern African populations were separated from western and central Africa Senegalia senegal is symbiotic with soil microorganisms, especially within the Sudano-Sahalian region. rhizobia and Arbuscular Mycorrhizal Fungi (AMF). Rhizobia contribute Based on cytology, S. senegal was reported to consist of diploids only to the global nitrogen cycle (Sprent, 1994), and a number of different (Atchison, 1948; Bukhari, 1997a, 1997b; Oballa and Olng'otie, 1993). rhizobial taxa and strains establish nitrogen-fixing nodules on S. senegal However, Assoumane et al. (2013) observed tetraploids in three differ- roots (Bakhoum et al., 2014;