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In recent years, so-called ‘lost crops’ have been appraised in a number of reviews, among them Lablab purpureus in the context of African vegetable species. This crop cannot truly be considered ‘lost’ because worldwide more than 150 common names are applied to it. Based on a comprehensive literature review, this paper aims to put forward four theses, (i) Lablab is one of the most diverse domesticated legume species and has multiple uses. Although its largest agro-morphological diversity occurs in South Asia, its origin appears to be Africa. (ii) Crop improvement in South Asia is based on limited genetic diversity. (iii) The restricted research and development performed in Africa focuses either on improving forage or soil properties mostly through one popular cultivar, Rongai, while the available diversity of lablab in Africa might be under threat of genetic erosion. (iv) Lablab is better adapted to drought than common beans (Phaseolus vulgaris) or cowpea (Vigna unguiculata), both of which have been preferred to lablab in African agricultural production systems. Lablab might offer comparable opportunities for African agriculture in the view of global change. Its wide potential for adaptation throughout eastern and southern Africa is shown with a GIS (geographic information systems) approach.
So-called ‘lost crops’ have been appraised in a number of reviews in recent years, among them Lablab purpureus (L.) Sweet, one of traditional African vegetables (NRC 2006). Information on neglected crops such as lablab is typically scattered over a range of journals, reports, or manuscripts, many of which will probably never be published and, therefore, remain inaccessible to most researchers. Recent compilations of information promoting the ‘conservation and use of underutilized and neglected crops’ (e.g., the series by IPGRI of the same name; Hammer et al. 2001), however, have usually excluded lablab because the species has attracted certain attention in the science literature, often far more than other neglected crops (J. Heller, pers. comm. 2003). Despite its representation in the literature, however, it can be argued that lablab truly qualifies as ‘underutilized’ given its many attributes, potential uses and adaptation.
Lablab is an ancient crop and has been documented by archaeo-botanical finds in India prior to 1500 BC (Fuller 2003) and at Qasr Ibrim in Egyptian Nubia from the 4th century AD (Clapham and Rowley-Conwy 2007). Despite its label of ‘underutilized’, however, substantial areas of lablab are sown in certain tropical regions, either as a sole crop or in mixed production systems. Its popularity may also be demonstrated by the large number of more than 150 local names reported by various authors and on databases (e.g., Westphal 1974; Kay 1979; MMPND 2005). Lablab is the third most important vegetable in the central and south-western parts of Bangladesh after eggplant (Solanum melongena) and taro (Colocasia spp.) and is reported to have a total production area in the region of approximately 48,000 ha (Rashid et al. 2007). However, the limited production data available suggest that yields are low. The species is largely cultivated as a systems’ component of homegardens or mixed cropping schemes, whose specific contribution to the overall system is usually not recorded. It has been documented as part of traditional production systems, such as those based around irrigated agriculture in the oases of Oman (Gebauer et al. 2007), homegardens in Nepal (Gautam et al. 2008), India (Kumar and Ramakrishnan 1990; Peyre et al. 2006), Bangladesh (Mir et al. 2004), Thailand (FAO 1999), and other tropical countries (Table 1).
The prime objective of this paper is to stimulate debate and focus on a crop whose striking diversity, uses and adaptation might be lost in Africa, its cradle, as it continues to be overlooked in current farming systems research and development. We also highlight the genetic diversity of the species so it might be applied to plant improvement efforts, including those in Asia, which are currently based on limited genetic diversity. The paper focuses on recent progress in plant improvement and genetic resources based on a comprehensive review of scientific literature from the mid 1990s to the present and so builds on the previous reviews of the crop by Schaaffhausen (1963), Hendricksen and Minson (1985), Shivashankar and Kulkarni (1989), and Murphy and Colucci (1999).
This paper also brings together and builds on the insights of diversity and domestication of the species provided in a number of previous studies over the last 8 years (Pengelly and Maass 2001; Maass et al. 2005; Tefera 2006; Maass and Usongo 2007; and Venkatesha et al. 2007), and it offers new insights into the species’ eco-geography based on passport data from 643 herbarium specimens and germplasm accessions collected from Africa (Ramme, 2002).
The probability of occurrence and potential use of lablab throughout eastern and southern Africa can be estimated by using passport data from a range of germplasm accessions and herbarium specimens as input into the FloraMap® program (Jones and Gladkov 1999; Jones et al. 2002), and by subsequently calculating and mapping the distribution probability based on climatic similarities. The resulting map (Fig. 4a) is in contrast to that generated by a database on tropical forages and derived primarily from known adaptation of widespread forage cultivars, such as cvs. Rongai or Highworth (Fig. 4b; Cook et al. 2005). While the tropical forages mapping suggests that large parts of eastern Africa are only marginally suited to the species, the analysis using passport data indicated that many accessions were collected from precisely some of those regions defined as “marginally suited” (Fig. 4a). Such divergent outcomes from GIS analyses can be expected when different ecotypes of a species are included (Jones and Gladkov 1999), as is the case here. The integrity of the divergence between the adaptation maps based on different ecotypes is supported by on-the-ground adaptation studies in southern Africa, where cvs. Rongai and Highworth were deemed to be unsuitable due to long vegetative phases that made them prone to early frosts or drought and impeded seed production (Maass et al. 2003; Whitbread and Pengelly 2004). Overall, the two maps demonstrate the wide potential range of adaptation for this species in Africa, depending both on specific genotypes (cultivars) and its purpose of use(s).
Few germplasm or herbarium collections originated from West and Central Africa. However, it would be expected that the species be adapted over a large proportion of that region given its rainfall and latitude. Widespread adaptation in West and Central Africa is supported by the forage accession analyses’ prediction of adaptation in the region (Fig. 4b).
The provocative title on whether or not L. purpureus is a crop lost for Africa aims to stimulate consideration of this versatile, variable and adaptable crop resource and avoid its loss. While the current initiatives to develop this underutilized plant for food and feed in Africa continue to be founded on a very narrow genetic base, and often on plant types selected for forage rather than pulses or vegetables, there is every reason for concern that known and existing biodiversity, which may be more suited to Africa and its range of climates, is being overlooked.
Adebisi and Bosch (2004) summarized that lablab has considerable promise as a crop species because its grain yields can be higher than those of cowpea and its spectrum of adaptability to differing ecological conditions is wider than for any other leguminous plant. However, not enough is known about adaptation to drought across the species (Ewansiha and Singh 2006). Even less information exists about the physiological mechanisms of that adaptation. The history, success and failure of lablab evaluation in various African environments, either as a crop or forage, have clearly been based on narrow genetic diversity and a few commercial cultivars, some of which were initially selected for their forage value only. Basing decisions on the potential value of the crop in Africa on results from this limited genetic base will undoubtedly lead to the risk that the species as a whole may be discarded (Maass et al. 2003). A wider range of diversity exists and is available from the world’s genebanks, including African indigenous materials. And this wider range of germplasm needs to be evaluated in future work. This may not only provide new insights into the potential role of lablab, in semi-arid regions in particular, but such an approach may also aid in ensuring that indigenous germplasm is conserved.
Due to its drought tolerance, lablab might offer comparable opportunities for African agriculture in the view of global change. The IPCC (2007) report indicates that many semi-arid areas, including southern Africa, will suffer a decrease in water resources due to climate change. Thornton et al. (2002) mapped the possible changes in production systems over sub-Saharan Africa and came to the conclusion that some of the existing cropping systems may decrease in area.
The mutual benefit and potential collaborations arising from the exchange of materials and knowledge between African and Asian researchers will hopefully have been stimulated during the First International Lablab Meeting near Arusha, Tanzania, in March 2008. Improved, high-yielding cultivars from drought-prone areas in India could contribute to African food security in regions with similar climates. Genetically distant African landraces may offer to the South Asian breeding programs new sources for pest and disease resistance together with other important traits. Collecting special purpose germplasm from semi-arid regions, such as in Namibia, where the wild L. purpureus subsp. uncinatus var. rhomboïdeus has been recorded (Verdcourt 1970) and which has never been included in any screening program, may add needed traits for future breeding programs.
This paper, together with an international meeting to stimulate collaborative activities among African and Asian researchers, was generously supported by the Kirkhouse Trust, UK. S.C. Venkatesha’s PhD thesis research is greatly benefiting from supervisions by Dr. T.H.N. Ellis (JIC, UK), Dr. P.H. Ramanjini Gowda and Dr. M. Byre Gowda (both UAS Bangalore, India). The following are the affiliations for personal communications: Dr. M. Byre Gowda, UAS, GKVK Campus, Bangalore 560 065, Karnataka, India, e-mail: email@example.com; Prof. Dr. J. Heller, University of Applied Sciences RheinMain, Rüdesheimer Str. 5, 65366 Geisenheim, Germany, e-mail: firstname.lastname@example.org; Prof. Dr. M.G. Kinyua, Moi University, PO Box 1125-30100, Eldoret, Kenya, e-mail: email@example.com; Dr. D.A. Vaughan, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba 305-8602, Ibaraki, Japan, e-mail: firstname.lastname@example.org.
Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
Elaborated from a presentation at the International Symposium “Underutilized plants for food, nutrition, income and sustainable development”, 3–7 March 2008, Arusha, Tanzania; organized by ICUC, GFU, AVRDC, GlobalHort, Bioversity International, PROTA, and ISHS.