Jens Gebauer

Effects of transformation processes on plant species richness and diversity in homegardens of the Nuba Mountains, Sudan

Traditional homegardens (HGs) are considered to harbor high levels of plant diversity and have been therefore characterized as sustainable agro-ecosystems suitable for on-farm (incl. circa situm) conservation of plant genetic resources. While the functional structure of traditional HGs is poorly understood specifically for semi-arid and arid regions, their plant species richness and diversity is increasingly threatened by recent and fast evolving agricultural transformation processes. This has been particularly claimed for traditional jubraka HG systems of Sudan. Therefore, sixty-one HGs in four villages of the Nuba Mountains, South-Kordofan Province, Sudan, were randomly selected, geographically recorded and plant richness and abundance determined and plant diversity parameters calculated. In addition, socio-economic household data were assessed by interviews and soil samples taken to allow a comprehensive analysis of putative factors affecting HG plant diversity across different villages, levels of commercialization and plant species composition based clusters. A total of 110 species from 35 plant families were grown in the HGs along with 71 ornamentals. Perennial species accounted for 57xa0% including 12 indigenous fruit tree (IFT) species and six exotic fruit tree species. Mean species richness of useful plant species (excluding ornamentals) per HG was 23 (range 6–46). On average, 41xa0% of the 23 species per HG were of exotic origin, however, with a large range (21–83xa0%) among locations. Mean diversity and evenness indices were 1.46 (range 0.49–2.42) and 0.48 (0.15–0.87), respectively. The level of commercialization of HGs only marginally affected species diversity measures although the species richness was significantly higher for commercial than subsistence HGs. Species richness was higher on lower (6.6–7.2) pH soils. IFT richness was highly variable, but non-significantly different across the four locations. Plant species richness and diversity was high in comparison with other HG systems in semi-arid regions. Cluster analysis was found to be a valuable tool to classify HGs and to extract homogeneous HG types with low, intermediate and high richness and diversity. In addition, the share of exotic and ornamental species in HGs indicated a trend towards the loss of traditional farming practices, particularly in areas with good market access. The data did not indicate the hypothesized loss of inter-specific diversity due to commercialization and species richness was numerically even higher for market-oriented HGs compared to subsistence ones.

Identification of mango (Mangifera indica L.) landraces from Eastern and Central Kenya using a morphological and molecular approach

Local mangos (Mangifera indica L.) are highly valued for home consumption in rural Kenya and are regarded by the local population to be comparatively drought tolerant and less susceptible to pests and diseases than the improved varieties. These are characteristics which make them interesting for improvement and breeding purposes. To date, research on Kenyan mangos has mainly focused on introduced and commercial varieties, whereas information on local varieties and landraces is lacking. We present the first comprehensive morphological and molecular characterisation of local mango landraces from Eastern and Central Kenya. Thirty-eight local mango trees were sampled and characterized by 75 selected qualitative (44) and quantitative (31) morphological descriptors selected from the descriptor list developed for mango by Bioversity International (former IPGRI). Hierarchical cluster analysis was performed using first all variables and finally only 10 selected key descriptors. Additionally, dried mango leaves from the same 38 trees were used for molecular classification with 19 simple sequence repeat markers. Genetic relatedness between the mango samples was visualized using a dendrogram based on Nei’s genetic distance and Neighbor Joining methods. Morphological characterisation resulted in six distinct clusters, and molecular analysis in eight clusters, which partly supported the morphological classification. Four of the eight molecular clusters were consistent and molecular results confirmed morphological classification in these cases. Identification of local mango landraces using morphological traits can be considered as satisfying under field conditions, e.g. for rootstock identification in nurseries, but environmental conditions may influence the results. Molecular marker analysis is more expensive, but independent from environmental influences and thus suitable for identification of landraces in field genebanks and for breeding purposes. Outcomes of the present study can form the basis for urgently needed future conservation efforts, including circa situ conservation on farms and the development of ‘conservation through use’ strategies for local mango landraces in Kenya.

Horizontal nutrient flows and balances in irrigated urban gardens of Khartoum, Sudan

The role of urban agriculture (UA) for the supply of fresh vegetables, fruits and meat for local markets is well known. The periodically flooded Gerif soils on the River Nile banks in the core of Khartoum city harbour vegetable gardens that supply perishable leafy vegetables with a short life cycle. In an effort to assess their sustainability and possible negative environmental impact we used a horizontal balance approach to determine the nutrient use efficiency of four intensively cropped UA gardens. Two of the gardens were located in downstream lowlands (L1 and L2) and the other two belonged to the upstream highlands (H1 and H2). The river sediments contributed on average 873xa0kg nitrogen (N), 6.5xa0kg phosphorus (P), 6.8xa0kg potassium (K) and 8,317xa0kg carbon (C) per hectare in lowland gardens, while only 289, 1.6, 2.5 and 1,938xa0kgxa0N, P, K and C ha−1 reached the highlands. The farmers’ management in all four gardens resulted in horizontal N and C surpluses of 75–342xa0kgxa0Nxa0ha−1xa0year−1 and 798–6,412xa0kgxa0Cxa0ha−1xa0year−1, in contrast to P and K for which negative balances up to −45xa0kg P ha−1 year−1 and −583xa0kgxa0Kxa0ha−1xa0year−1 were recorded. While the River Nile floods as important N and C source contribute significantly to soil fertility maintenance, the negative P and K balances call for a better integration of UA gardening with livestock husbandry and the regular addition of animal manure in these cropping systems.

A note on baobab (Adansonia digitata L.) in Kordofan, Sudan

The isolated Sudanese baobab (Adansonia digitata L.) populations, located at the northernmost limit of the East African distributional range of the species, are regarded as important genetic resources. The morphological variation in fruits of selected baobab trees in Kordofan, Sudan, was evaluated by sampling fruits and assessing their characteristics. Furthermore, locations and stem diameter at breast height of 240 baobabs were mapped for a stand in Kordofan. Our preliminary results indicated a high diversity in fruit phenotypes. Ventricose, crescent-shaped, globose and fusiform fruit types were identified. Fruit shape varied between trees but was consistent within each individual tree. Percentage of fruit pulp varied between the different fruit types with 14, 15, 18, and 21xa0% recorded for ventricose, fusiform, crescent-shaped and globose fruits, respectively. Interesting was also the observation of baobab morphotypes that retained leaves during the dry season. Variation in leaf morphology could also be recognised. Measurements of baobab trees revealed a density of 0.72 individuals ha−1. Stem diameters ranged from 0.06 to 4.77xa0m. The size class distribution (SCD) showed an inverse J-shaped curve with a SCD slope of −0.57 which indicates a viable regenerating population. Based on the results recorded, enhancement of scientific research activities on the almost unstudied baobabs in Kordofan, Sudan is highly recommended.

The African baobab (Adansonia digitata, Malvaceae): Genetic resources in neglected populations of the Nuba Mountains, Sudan

UNLABELLEDn•nnnPREMISE OF THE STUDYnAdansonia digitata L. is one of the most important indigenous fruit trees of mainland Africa. Despite its significance for subsistence and income generation of local communities, little is known about the genetic and morphological variability of East African populations of A. digitata, including those of Sudan. The aim of the current study, therefore, was to analyze genetic and morphological variability of different baobab populations in Kordofan, Sudan and to estimate the effect of human intervention on genetic differentiation and diversity.•nnnMETHODSnA total of 306 trees were randomly sampled from seven spatially separated locations in the Nuba Mountains, Sudan, to cover a wide range of differing environmental gradients and management regimes (homesteads and wild). Genetic analyses were conducted using nine microsatellite markers. Because of the tetraploid nature of A. digitata, different approaches were applied to estimate patterns of genetic diversity. Investigations were completed by measurements of dendrometric and fruit morphological characters.•nnnKEY RESULTSnGenetic diversity was balanced and did not differ between locations or management regimes, although tendencies of higher diversity in homesteads were observed. A Bayesian cluster approach detected two distinct gene pools in the sample set, mainly caused by one highly diverse population close to a main road. The variability of tree characters and fruit morphometries was high, and significantly different between locations.•nnnCONCLUSIONSnResults indicated a rather positive effect with human intervention. The observed populations provide a promising gene pool and likely comprise ecotypes well-adapted to environmental conditions at the northern distribution range of the species, which should be considered in conservation and management programs.

Africa’s wooden elephant: the baobab tree (Adansonia digitata L.) in Sudan and Kenya: a review

Wild edible fruits hold great potential for improving human diets, especially in agricultural societies of the developing world. In Africa, a well-known supplier of such fruits is the baobab (Adansonia digitata L., Malvaceae), one of the most remarkable trees of the world. Several studies in different African countries have highlighted this indigenous fruit tree as a priority species for domestication and expanded use. However, internationally available information on baobab in East Africa, particularly in Sudan and Kenya, remains scarce. This review aims to shed light on the ecology, diversity and current level of utilization of baobab in East Africa in order to facilitate domestication and conservation of the species. A list of priority research areas is provided at the end of the review to encourage further studies and investment in this unique plant taxon.

Current knowledge and breeding perspectives for the miracle plant Synsepalum dulcificum (Schum. et Thonn.) Daniell

Synsepalum dulcificum, an African native shrub, is a valuable species. All plant parts are of medicinal importance whereas the fruit known as magic berry, miracle berry, or sweet berry is consumed fresh. Surprisingly, very little is known on the species in terms of genotypes utilization and breeding. In this review we recalled the uses and importance of the species and suggested research avenues for an accelerated growth and fruit production. Synsepalum dulcificum is rich in glycoprotein and is an excellent natural sweetener and also a good candidate for the synthesis of drugs against diabetes. Furthermore, S. dulcificum has high content in phytochemical substances (e.g. (+)-epi-syringaresinol, vanillic acid, cyanidin-3-monogalactoside, and quercetin-3-monogalactoside) with various health and food benefits. Data on the nutrient content are limited. Likewise, knowledge on the reproductive biology and mating system is still narrow, combined with poorly developed horticultural practices. To fully exploit the potential of S. dulcificum prospective actions include: (1) improving the propagation and growth abilities of the species, (2) improving knowledge of floral biology and genetic diversity, (3) understanding the phenological phases of the species, gene expressions and how this contributes to metabolites accumulation and (4) improving genotypes for beverages, cosmetics and pharmaceutical industries and other value chains.

Carbon and nutrient fluxes and balances in Nuba Mountains homegardens, Sudan

Management intensification has raised concerns about the sustainability of homegardens in the Nuba Mountains, Sudan. This study aimed at assessing the sustainability of these agroecosystems following the approach of carbon (C) and nutrient balances. Three traditional (low input) and three intensified (high input) homegardens were selected for monitoring of relevant input and output fluxes of C, nitrogen (N), phosphorus (P) and potassium (K). The fluxes comprised those related to management activities (soil amendments, irrigation, and biomass removal) as well as estimates of biological N2 fixation, C fixation by photosynthesis, wet and dry deposition, gaseous emission, and leaching. Annual balances for C and nutrients amounted to −21xa0kgxa0Cxa0ha−1, −70xa0kgxa0Nxa0ha−1, 9xa0kgxa0Pxa0ha−1 and −117xa0kgxa0Kxa0ha−1 in high input homegardens and to −1,722xa0kgxa0Cxa0ha−1, −167xa0kgxa0Nxa0ha−1, −9xa0kgxa0Pxa0ha−1 and −74xa0kgxa0Kxa0ha−1 in low input homegardens. Photosynthesis C was the main C input flux with averaged of 7,047 and 5,610xa0kgxa0Cxa0ha−1xa0a−1 in high and low input systems, respectively. Biological N2 fixation (17xa0kgxa0N ha−1xa0a−1) was relevant only in low input systems. In both systems, the annual input of 77xa0kgxa0Kxa0ha−1 through dust was highly significant and annual gaseous C losses of about 5,900xa0kgxa0Cxa0ha−1 were the main C loss. In both garden types, the removal of biomass accounted for more than half of total nutrient exports of which one-third resulted from weeding and removal of plant residues and two-third from harvest. The observed negative nutrient balances may lead to a long-term decline of crop yields. Among other measures the reuse of C and nutrients in biomass removals during the cleaning of homegardens may allow to partially close C and nutrient cycles.

The role of homegardens and forest ecosystems for domestication and conservation of Ziziphus spina-christi (L.) Willd. in the Nuba Mountains, Sudan

Iterative domestication processes by humans such as selection, translocation and cultivation are known to affect the morphological and genetic diversity of tree species. Since many of these species occur also in human-created homegardens (HG) this type of agroecosystem therefore represents an ideal setting to study such domestication processes. The threatened indigenous fruit tree Ziziphus spina-christi occurs in HGs and forests of the Nuba Mountains, Sudan, and was therefore selected as a model species. Five locations were sampled and the geographical position of 250 trees determined. Each location was subdivided into HG and forest sites. The diversities of morphological traits and amplified fragment length polymorphisms were assessed to study variation within and among locations and sites. Diversity of dendrometric parameters and fruit morphometries was high and differed significantly among locations. Environmental parameters affected dendrometry and fruit size, but applied regression models were of low explanatory power. Although statistically not significant, mean fruit measures were continuously larger in HGs than in forests. Higher genetic diversity was observed in HG samples. Larger dendrometric and fruit morphometric traits are likely to result from better growing conditions in HGs and/or human selection of germplasm. This is in line with the higher genetic diversity in HGs which may be a consequence of the admixture of germplasm from different origins planted in HGs. Z.xa0spina-christi underwent incipient steps of domestication. High genetic diversity in HGs suggests those as valuable spots of improved germplasm and for on-farm conservation purposes.

Grewia flavescens: a potential horticultural crop?

Traditionally agricultural research has given little attention to underutilized or neglected crops. Grewia flavescens Juss., the donkey berry, is a fruit species which is found throughout semi-arid and sub-humid tropical Africa and sometimes cultivated in homegardens. The species is also known for its ornamental value and is used as a vegetable, fodder and in basketry. In Niger its fruits are mostly collected in the wild and sold at markets. The fruits are used as food and for traditional medicinal treatments. To promote this interesting neglected taxon as a horticultural crop, information on its germplasm diversity and cultivation practices is urgently needed.