Diversity and distribution patterns of enset landraces in Sidama, Southern Ethiopia

Diversity and distribution of enset landraces (clones) were investigated in 300 randomly selected peasant households at ten different locations in the Sidama region of Ethiopia using presence-or-absence data. A total of 86 named landraces were recorded, making the region an area of remarkably high enset landrace diversity. A substantial fraction of the landraces had a restricted distribution range and low abundance while a number were moderately common with the remaining few being cosmopolitan. Regional distribution was positively correlated with local abundance, such that more widespread landraces were also typically more abundant (r = 0.78, p < .01). Landrace diversity was not evenly distributed throughout the region, the highest diversity being recorded in mountain areas (r = 0.71, p < .05). Farmers exchange planting materials extensively, resulting in a fairly high (up to 70%) coefficient of similarity among sites. Implications for the collection and conservation of enset genetic resources are discussed.     

Genetic erosion of Ethiopian tetraploid wheat landraces in Eastern Shewa,Central Ethiopia

Ethiopia is a centre of diversity and hosts rich genetic resources of tetraploid wheats. Through time, the wheat materials were subject to genetic erosion. Closer investigation was made to assess the status of loss, and identify the possible causes by studying two districts from East Shewa. Information from primary and secondary sources was reviewed and analysed. Farmers identified 26 tetraploid wheat landraces (21 from Akaki and 17 from Ejere), which were once widely grown in the area. Of these, only six were currently available. Compared to the formerly available number of landraces, the loss of diversity in the study area was estimated to be 77%. In the Ejere locality, the loss was 100% before the launching of the on farm landrace conservation programme, and for Akaki it was 95%. Major factors that contributed to the loss include: (1) introduction and expansion of bread wheat varieties; (2) expansion of tef; (3) lack of a mechanism to re-supply seeds of tetraploid wheat landraces; (4) decline in size of landholdings; (5) changes in land use and cropping patterns; (6) lack of policy support; and (7) expansion of improved tetraploid wheat varieties. The lessons from this study underscore the importance of strengthening the local seed supply system as a prerequisite for sustaining on farm conservation of landraces. Moreover, it is necessary to initiate diversity studies focusing on the distribution and status of tetraploid wheat landraces across the country. Complementing these by molecular analyses is essential in order to assess the genetic distinctness of the landraces.     

A new yam bean (Pachyrhizus spp.) interspecific hybrid

The yam bean (Pachyrhizus spp.) is a legume tuber / root crop locally grown in Central America, South America and Asia. The tuber is usually consumed raw for its refreshing taste and high moisture content. A recently found P. tuberosus type from a small ecogeographic region in the tropical lowlands of Peru has a high tuber dry matter content and this so-called Chuin-Type is consumed like manioc. This study was conducted to determine the possibility to use the Chuin-Type as a source to incorporate high dry matter into the remaining yam bean gene pool. Three P. tuberosus (Chuin) accessions were crossed with 15 P. ahipa accessions from the Andean highlands resulting in six successful interspecific hybridisations. Successful crosses were confirmed by morphological and agronomical traits as well as multivariate statistics. All hybrid plants were fertile and vigorous. Owing to the fertility and vigour of interspecific hybrids it is assumed that a hybrid between P. tuberosus and P. ahipa might already evolved in the area of origin and that interspecific hybridisation is appropriate to improve the tuber dry matter content in the yam bean which might give the crop new forms of food and processing use.     

Genetic Nature of Yams (Dioscorea sp.) Domesticated by Farmers in Benin (West Africa)

‘Domestication’ is a traditional farmers’ practice reported for yams (Dioscorea sp.) in Benin (West Africa). It involves introducing ‘spontaneous’ (naturally occurring) yams, supposedly wild (D. abyssinica and D. praehensilis), in varieties of the D. cayenensis–D. rotundata cultivated species complex. In this study, we established the genetic nature of ‘predomesticated’ yam plants using the amplified fragment length polymorphism (AFLP) technique. A total of 213 accessions, consisting of 32 predomesticated yams, 70 D. cayenensis–D. rotundata, 86 D. abyssinica and 25 D. praehensilis yams were analysed. Using 91 AFLP markers, three groups of accessions were distinguished, broadly corresponding to the above botanical species. Of the 32 predomesticated accessions, 16% were clustered with D. praehensilis, 37% with D. abyssinica and the remaining 47% with D. cayenensis–D. rotundata. These results demonstrated the use of wild plants by farmers in their domestication process, and suggested that plants derived from intervarietal and interspecific hybridisation may also be subject to this process. This study has shown that through domestication farmers influence and increase the genetic diversity in yam by using sexual reproduction of wild and possibly cultivated yams.     

Inverse Sequence-tagged Repeat (ISTR) Analysis of Genetic Variability in Forest Coffee (Coffea arabica L.) from Ethiopia

Genetic diversity in forest coffee (Coffea arabica L.) was estimated using inverse sequence-tagged repeat (ISTR) markers. One hundred ninety two samples representing 16 populations of C. arabica from four regions of Ethiopia were analyzed with 12 pairs of forward and backward ISTR primer combinations. A total of 144 reproducible bands were generated out of which 37 (25%) were polymorphic and scored as present (1) or absent (0) data matrix. This data was used to compute Jaccard coefficient to estimate genetic variability among all possible pairs of samples. The proportion of polymorphic bands within populations ranged from 19% for Bale-3, to 54% for Walega-2 populations. Un-weighted pair group method with arithmetic mean (UPGMA) based cluster analysis generated two clusters at 56% similarity value. The samples were clustered on the basis of their geographical origin, which could be attributed to a few region specific banding patterns detected. However, within regions most of the samples failed to cluster on the basis of their respective populations, which may be due to the presence of substantial gene flow between local populations in the form of seedlings carried out by farmers. The results may provide information to develop strategies for in situ conservation.     

Current status of coffee (Coffea arabica L.) genetic resources in Ethiopia: implications for conservation

The aim of this article is to provide an overview of the current situation of coffee genetic resources that are dwindling at an alarming rate in Ethiopia, the centre of diversity of Coffea arabica. Firstly, we describe the coffee growing systems (forest coffee, semi-forest coffee, garden coffee and plantation coffee) and recent research on the genetic diversity of the coffee planting material associated with those systems. Whilst the maximum genetic diversity revealed by DNA-based markers is found in the forest coffees of the south-western highlands, the natural habitat of C. arabica, the taxonomy of coffee landraces is particularly rich in garden coffee systems located in ancient growing zones such as Harerge in eastern Ethiopia. After reviewing the factors involved in the genetic erosion of the Ethiopian genepool, we give an update on the status of coffee genetic resources conserved ex situ in the field genebank of the Jimma Agricultural Research Centre, with 4,780 accessions spread over 10 research stations located in the main production areas, and in the main genebank of the Institute of Biodiversity Conservation located in Choche (Limu) with 5,196 accessions conserved. Lastly, we mention the in situ conservation operations currently being implemented in Ethiopia. Improving our knowledge of the genetic structure of Ethiopian forest and garden coffee tree populations as well as genetic resources conserved ex situ will help to plan the future conservation strategy for that country. To this end, modern tools as DNA-based markers should be used to increase our understanding of coffee genetic diversity and it is proposed, with the support of the international scientific community and donor organizations, to undertake a concerted effort to rescue highly threatened Arabica coffee genetic resources in Ethiopia.

The major Italian landraces of lentil (<Emphasis Type="Italic">Lens culinaris</Emphasis> Medik.): Their molecular diversity and possible origin

The eleven most known landraces from central and southern Italy were analysed using ISSR markers on 15 randomly chosen individuals for each landrace, with the aim of assessing genetic variation within and among landraces and possibly ascertaining their origin and genetic relationships. A total of 164 loci were observed, 128 of which (78.05%) were polymorphic. Gene diversity over all landraces was I = 0.3759. The highest within-landrace diversity was observed in samples from the Apennine ridge and for one Sicilian landrace; on the other hand, samples from the small Sicily islands were less variable. Principal Component Analysis and AMOVA allowed the discrimination of groups of landraces with higher similarity. Analyses indicate that the small Sicily islands landraces are very closely related to one another and seem to be derived from the peninsular material; moreover, they help disclose relationships among geographically close landraces. The knowledge so acquired can, therefore, contribute to elaborate strategies for increasing the economical value of élite landraces and to protect producers from frauds.     

Geographic variation in tetraploid wheat (Triticum turgidum spp. turgidum convar. durum) landraces from two provinces in Ethiopia

There is considerable wealth of genetical and morphological variation in tetraploid wheat collected from Ethiopia by past expeditions. Several authors have speculated on the reasons for this concentration of diversity so far removed from the centre of origin of wheats in West Asia. The present study reports results of evaluation carried out on material collected in the early 1970's from Ethiopia. The landraces from the two provinces Shewa and Tigray were found to be distinctly different. This divergence was attributed to the differences in environmental conditions between them. Wide differentiation among landraces within each province was also present. The Ethiopian farmer's practice of growing composite cultivars in the field has resulted in bulk samples of Ethiopian landraces containing several agrotypes. The proportion of total variance due to differences among agrotypes within landraces was by far the greatest found in this study, followed in most cases by the variation among landrace populations within provinces which exceeded, in turn, the variation between province gene pools. The optimal strategy for further germplasm collections and implications for improvement and conservation in locally-based community gene banks are discussed.     

Genetic Diversity and Phylogenic Relations Among Sahelian Sorghum Accessions

To establish the genetic relationship among Sahelian sorghum [Sorghum bicolor (L.) Moench S.L.] landraces from Burkina Faso were submitted to electrophoretic analysis for 10 enzymatic systems and 18 loci. Four enzymatic systems (ADH, LAP, MDH, PGD) and five loci revealed polymorphism both within and among landraces. Thirty-eight per cent of the landraces were monomorphic in all the 18 loci. The genotypic frequencies in most of the landraces deviated markedly from Hardy–Weinberg proportions due to a major heterozygote deficit, the landrace being homozygous or a mixture of homozygotes. Multivariate analysis yielded three main groups, containing native landraces and five minors, containing introduced cultivars, randomly distributed over the territory. The pattern of allelic occurrence was random and unrelated to external selection pressures. The major diversity among landraces appears to be from genetic shift caused by farmers’ selection of their seeds. It could also be due to the low rates of outcrossing (19%) and migration (0.06) prevailing in the set.     

Physico-chemical characterisation of yam (Dioscorea alata L.) tubers from Vanuatu

The objectives of this study were: (1) to analyse the physico-chemical characteristics of 48 Dioscorea alata varieties representing a core sample of the Vanuatu national germplasm collection; (2) to relate those characteristics with the varieties eating quality; and (3) to assess the possibility of selecting varieties according to their chemotype. Overall, 331 accessions were collected from 15 different islands of Vanuatu, planted in an ex situ germplasm collection and described during 3 years. The 48 varieties included in the core sample were selected according to their island of origin, eating quality, tuber shape, tuber flesh colour and morphotype. Analyses of their tubers were made for percentage dry matter, starch, amylose, lipids, minerals, proteins, sugars and gelatinisation temperature range. Significant variation exists for each of these characteristics except for gelatinisation temperature. Varieties with good eating quality are characterised with high dry matter, starch and amylose contents. Chemotypes appear to be genetically controlled and further screening of germplasm and/or breeding will have to take into consideration these characteristics, important for farmers’ adoption.     

The nitrogen nutrition of yam (Dioscorea spp)

Abstract

Information on the nitrogen (N) nutrition of yam (Dioscorea spp) is limited. Our objective was to elucidate the factors controlling N uptake by D. rotundata and D. alata. We analyzed results obtained with improved cultivars of these species grown in three field experiments among which ¹⁵N-fertilizer was used in one. Plant biomass production, leaf area index (LAI), root length density, N and ¹⁵N uptake by the plant were measured in these experiments. Nitrogen uptake was controlled in both species by plant demand and N inputs. A positive relation was observed between N uptake and LAI. Despite the small root system, the ability of the plant to take N up was high. The amount of N derived from the fertilizer recovered in the plant was explained by total N uptake. Finally, avenues to improve the low nitrogen fertilizer recovery (<20%) in yam are discussed.     

Genetic and Phenotypic Diversity in Downy-mildew-resistant Sorghum (Sorghum bicolor (L.) Moench) Germplasm

Genetic and phenotypic diversity among randomly selected 36 downy-mildew-resistant sorghum accessions were assessed, the former using 10 simple sequence repeat (SSR) marker loci and the latter using 20 phenotypic traits. The number of alleles (a _j ) at individual loci varied from five to 14 with an average of 8.8 alleles per locus. Nei's gene diversity (H _j ) varied from 0.59 to 0.92 with an average of 0.81 per locus. High gene diversity and allelic richness were observed in races durra caudatum (H _j = 0.76, a _j = 4.3) and guinea caudatum (H _j = 0.76, a _j = 3.8) and in east Africa (H _j = 0.78, a _j = 7.2). The regions were genetically more differentiated than the races as indicated by Wright's F _st. The pattern of SSR-based clustering of accessions was more in accordance with their geographic proximity than with their racial likeness. This clustering pattern matched little with that obtained from phenotypic traits. The inter-accession genetic distance varied from 0.30 to 1.00 with an average of 0.78. Inter-accession phenotypic distance varied from 0.01 to 0.55 with an average of 0.33. Eleven accession-pairs had phenotypic distance of more than 0.50 and genetic distance of more than 0.70. These could be used as potential parents in a sorghum downy mildew resistance-breeding program.     

Species Diversity in Wheat Landrace Populations from two Regions of Ethiopia

Wheat (Triticum spp.) landrace populations in Ethiopia are mostly species mixtures. However, no quantitative data is available with regard to their species components. We studied here 32 wheat landrace populations originating from two regions (Bale and Wello). A total of 2559 individual plants, 45–110 plants representing each population, were classified into their species components. Five tetraploid (2n = 4x = 28) and one hexaploid (2n = 6x = 42) wheat species were found in mixtures of varying proportions. These included the tetraploids Triticum durum Desf., Triticum turgidum L., Triticum aethiopicum Jakubz., Triticum polonicum L., Triticum dicoccon Schrank and the hexaploid Triticum aestivum L. Also found, however in a rare frequency, in two populations from Wollo was T. durum Desf. convar. durocompactoides Flaksb. (Triticum pyramidale Percival), which is a very dense spiked durum. Discriminant analysis using seven qualitative traits revealed 91.5% correct classification of the wheat species, beak awn and awn length with the most significant importance. Single species were found in eight of the populations; six were for T. durum and two for T. aethiopicum. Two to three species-combinations were the most frequent; a maximum of four species was recorded in one population. The highest diversity index (H′) observed was 0.44. T. durum was the most predominant species. The hexaploid T. aestivum was found in nine of the Wollo populations and, in one population, its frequency reached up to 35.5%. On altitudinal basis, no clear trend of clinal variation was observed both from the frequency distributions and H′ estimates. The results confirmed that Ethiopian wheats, despite the morphological overlaps, could be classified into their species components with high degree of certainty. For the future, therefore, genetic diversity estimations should be dissolved into their species components for more expeditious utilization and conservation of this important genetic resource.     

Genetic Diversity and Relationships of Wheat Landraces from Oman Investigated with SSR Markers

Little is known about genetic diversity and geographic origin of wheat landraces from Oman, an ancient area of wheat cultivation. The objectives of this study were to investigate the genetic relationships and levels of diversity of six wheat landraces collected in Oman with a set of 30 evenly distributed SSR markers. The total gene diversity, (H_T), conserved in the three durum wheat (Triticum durum desf.) landraces (H_T = 0.46) was higher than in the three bread wheat (Triticum aestivum L.) landraces (H_T = 0.37), which were similar to Turkish and Mexican bread wheat landraces calculated in previous studies. Genetic variation partitioning (G_ST) showed that variation was mainly distributed within rather than among the durum (G_ST = 0.30) and bread wheat (G_ST = 0.19) landraces. Based on modified Rogers’ distance (MRD), the durum and bread wheat landraces were distinct from each other except for a few individuals according to principal coordinate analysis (PCoA). One bread wheat landrace (Greda) was separated into two distinct sub-populations. A joint cluster analysis with other landraces of worldwide origin revealed that Omani bread wheat landraces were different from other landraces. However, two landraces from Pakistan were grouped somewhat closer to Omani landraces indicating a possible, previously unknown relationship. Implications of these results for future wheat landrace collection, evaluation and conservation are discussed.     

Genetic diversity in bambara groundnut (Vigna subterranea (L.) Verdc) landraces assessed by Random Amplified Polymorphic DNA (RAPD) markers

Genetic diversity in 12 landraces of bambara groundnut (Vigna subterranea), an indigenous African legume, was evaluated using Random Amplified Polymorphic DNA (RAPD) markers. DNA from individuals of each landrace was also analysed to determine the level of heterogeneity within landraces. RAPDs revealed high levels of polymorphism among landraces. The percentage polymorphism ranged from 63.2% to 88.2% with an average of 73.1% for the 16 RAPD primers evaluated. The construction of genetic relationships using cluster analysis groups the 12 landraces in two clusters. RAPDs are useful for the genetic diversity studies in V. subterranea and can identify variation within landraces.     

Genetic erosion of sorghum (Sorghum bicolor (L.) Moench) in the centre of diversity, Ethiopia

The Ethiopian region is characterised by a wide range of agro-climatic conditions, which accounted for the enormous resources of agro-biodiversity that exist in the country. The most important of these resources is the immense genetic diversity of the various crop plants in the country. Of these, one of the most on farm genetically diverse crops is sorghum. Since the advent of formal breeding in particular after green revolution, genetic diversity of most crops has been threatened worldwide. In order to assess on farm genetic erosion (GE), various research methodologies were employed. These were focused group interviews with 360 farmers, on farm monitoring and participation with 120 farmers, key informant interviews with 60 farmers and development agents, and semi-structured interviews with 250 farmers. Besides, diversity fairs were done with over 1200 farmers. Notwithstanding the complexity of assessing GE, it was assessed by various methods; namely, by temporal method (comparing 1960 and 2000 collections), area method, and semi-structured interview method at individual, community or wereda level and causes of varietal loss from other various perspectives. Farmers perceived GE as the reduced importance of the variety as indicated by lower proportion in the varietal portfolio. The five most important factors for varietal loss at individual farmers’ level were reduced benefit from the varieties, drought, Khat expansion, reduced land size and introduction of other food crops respectively. GE was not affected by wealth groups and ecological regions. Farmers do not make simple replacement as a strategic mechanism for genetic resources management. GE at regional level was quantified by temporal and spatial method. There was a complementation not rivalry between farmer varieties (FVs) and improved varieties (IVs). The whole process of GE is explained by three models, namely: Bioecogeographic enhanced genetic erosion model, Farmer induced genetic erosion model and Farmer-cum-bioecogeographic genetic erosion model. As aforementioned, sorghum genetic erosion behaviour is completely different from other food crops such as tetraploid wheat. The prediction in the late seventies that complete erosion of FVs by IVs by the end of the eighties, the principle of GE that competition between IVs and FVs, favours the former and results in the replacement of the latter is not valid in the context of sorghum in Ethiopia. Hence, maintenance of the on farm genetic diversity of sorghum is a reality but GE is rhetoric.     

RAPD Polymorphism of the White-Flowered Gourd (Lagenaria siceraria (Molina) Standl. Landraces and its Wild Relatives in Kenya

The present study was performed to investigate genetic diversity of Kenyan landraces of the white-flowered gourd (Lagenaria siceraria), which exhibits tremendous morphological variation. RAPD analyses were performed on 53 landraces of the cultivated species L. siceraria and 42 accessions of three wild species (40 L. sphaerica, 1 L. abyssinica, and 1 L. breviflora). A total of 432 polymorphic bands were detected using 54 primers. The four species were clearly differentiated from one another. Intra-specific variations were investigated with L. siceraria and its wild relative L. sphaerica. Landraces of the cultivated species collected from different ethnic communities or regions were differentiated. Morphological variations were not associated with RAPD variations. Bitter landraces collected in Maasai communities showed two specific RAPD bands. In the wild species, accessions collected from the eastern and western sides of the Great Rift Valley were genetically differentiated from each other. In both species, genetic and geographical distance matrices computed among all pairs of accessions were significantly correlated, implying that the observed geographical variation can be explained by the 'Isolation by distance model'. Progeny plants derived from a common mother in L. siceraria showed a low level of segregation in RAPD pattern, suggesting that collected landraces are cultivated, maintaining their inherent traits although they are monoecious and insect-pollinated, whereas the wild relative L. sphaerica showed a higher level of segregation. The morphological diversity observed among landraces of L. siceraria is the result of human selection and their genetic identities are maintained by inbreeding probably resulting from frequent self-pollination.     

Diversity Analysis of Garlic (Allium sativum L.) Germplasms Available in Nepal Based on Morphological Characters

A total of 179 garlic (Allium sativum L.) accessions were collected from various parts of Nepal in 2000. Each accession was planted in each of a plot of 2.25 m² at the Institute of Agriculture and Animal Science (IAAS) Horticulture farm (225 m asl) and at the Agriculture Research Station, Dailekh (1400 m asl) of Nepal Agriculture Research Council (NARC) in the first week of November 2000. All accessions were characterized for leaf erectness, leaf color, leaf wax, leaf cross section, bulb regularity, bulb skin color, bulb outer scales number, days to emergence, bulbing period, number of green leaves at 135 days after planting, days to maturity, plant height, bulb weight, bulb diameter, number of cloves per bulb, clove diameter and bulb yield. Data were analyzed by using principal component and cluster analysis procedures to reveal three major clusters. Four principal components were identified explaining more than 86% of total variation. Major characters included in the principal components were bulb weight, diameter, yield, number of cloves per bulb, maturity, plant height, number of green leaves at 135 days after planting, and bulbing period. The level of variation found in the collection showed the great potentiality of improving agronomic characters in garlic.     

Multivariate Analysis of Diversity of Tetraploid Wheat Germplasm from Ethiopia

The variability of 2420 plants of tetraploid (2n = 4x = 28, AABB genome) wheat germplasm representing 121 accessions from Ethiopia were evaluated for 23 agro-morphological traits at Debre Zeit Agricultural Research Center area, Akaki substation, during the 2003 main season using multivariate methods. This enabled to assess the extent and pattern of variation of the germplasm with respect to regions, altitude classes and species and to identify the major traits contributing to the diversity. The first three and two principal components explained about 83 and 80% of the total variance among regions and altitudinal class, respectively. In the first principal component plant height, days to heading, the length and density of the spike, and kernel color were the most important traits contributing to variation that explained about 50% of regional variance. Cluster analysis grouped the accessions into 15 clusters, with 9 accessions remaining ungrouped. Based on the observed patterns of variation, it is concluded that there exists great variation in the germplasm, which provides opportunities to be utilized for genetic improvement.