Horticultural Science
Permanent URI for this collectionhttps://etd.hu.edu.et/handle/123456789/41
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Item DIVERSITY OF CULTIVATED AND WILD YAMS (Dioscorea spp) IN SOUTHWEST ETHIOPIA BASED ON FARMERS MANAGEMENT PRACTICES, AGRO-MORPHOLOGICAL TRAITS AND NUTRITIONAL COMPOSITION(Hawassa University College of Agriculture, 2021) TSEGAYE BABEGE WOROJIEDIVERSITY OF CULTIVATED AND WILD YAMS (Dioscorea spp) IN SOUTHWEST ETHIOPIA BASED ON FARMERS MANAGEMENT PRACTICES, AGRO-MORPHOLOGICAL TRAITS AND NUTRITIONAL COMPOSITION Yam (Dioscorea spp) is a traditional crop that has long been cultivated in Ethiopia as a co-staple crop. Several yam species might have their origin in Ethiopia and are among those crops with wild relatives in the country. Though the genus Dioscorea is reported to show a wide range of variation, it has not been studied across its range of distribution. This study was investigated the diversity of wild and cultivated yams in Bench-Sheko and Sheka Zones, Southwest Ethiopia. Toward this effort, 5 studies were carried out. The first 2 studies were designed to investigate folk biosystematics, diversity and distribution and the local management practices of yams in Southwest Ethiopia. In the third study, accessions from South and Southwest Ethiopia were considered to investigate the diversity of yams based on agro-morphological traits. In the fifth study, we link two data sets to assess the knowledge of wild yam and the process of domestication. Lastly, we analyze the nutritional compositions based on selected yam landraces. We also have another study which is underway and was part of our initial project initiated with the objective of studying the true genetic diversity of yams using SSR marker. An ethnobotanical survey was conducted on 15 Kebeles in 5 districts of Bench-Sheko and Sheka Zones from Dec., 2016 to Nov., 2017. Data were collected using a semi-structured questionnaire from 272 households. Seventy-five yam accessions corresponding to 30 differently named landraces were used for morphological study. Sixty of the 75 accessions were collected in Kaffa, Bench-Sheko and Sheka Zones of Southwest Ethiopia. The rest represented previously collected accessions from Basketo, Gamo-Gofa and Wolaita areas of Southern Ethiopia. They were grown in RCBD with 2 replicates in 2018 at Hawassa University research field. The process of wild yam manipulation in Southwest Ethiopia was studied by linking two data sets derived from (1) ethnobotanical survey using 231 interviews and (2) morphological study using 47 selected accessions. Twelve landraces composed of different species and contexts were analyzed for nutritional composition in Addis Ababa at the Ethiopian Health and Nutrition Research Institute. Results obtained from ethnobotanical study suggest that there exists a systematic and welldeveloped folk naming and taxonomic system in Sheko and its environs. Sheko and Bench botany of yam recognizes 58 named individuals. These individuals are grouped into 3 well recognized ranks, namely sub-variety, variety and supra variety. Taxa assigned to each ranks have distinct features that mark them as members of a separate group. Farmers manage a wide range of morphological characters and some other attributes other than morphological ones for grouping of the taxa assigned to distinct groups. An account of each of these aspects and its link with the taxa recognized in the domain of formal science are presented. A folk biological classification of yam consisting of 4 taxonomic ranks is proposed. Our result showed much information of biological and functional aspects which can aid the taxonomic and genetic study of yams in Ethiopia. Our assessment also showed that there exists a wide range of yam diversity in Southwest Ethiopia. Altogether, 40 actually grown yam landraces, including those found in farms of unsampled households were recorded; making Bench-Sheko and Sheka Zones an area of notably high landrace diversity. The greatest number of these individuals had a narrow xviii distribution and low abundances, with a few being cosmopolitan. This was evident in a positive and significant correlation between distribution and local abundance, such that a few cosmopolitan landraces were locally more abundant. Maintenance and distribution range of landraces is related with the local management practices. A description of farmers’ decisions to the on-farm landrace maintenance is presented and implication for the collection and conservation of yam germplasm are suggested. Morphological diversity study based on 37 qualitative and 13 quantitative traits has shown a considerable variability among accessions of yam species studied. Our multivariate analysis showed that all the traits used were useful for capturing the variability among accessions, but 21 traits (17 of which are qualitative traits) were useful for capturing the variability among accessions of distinct species. The remaining traits were useful for capturing the variability among accessions within and between species, which could be exploited, if improvement need arises. The overall structure of morphological diversity is consistent with the locally perceived biota. Yet, no clear morphological variations were obtained among some differently/similarly named landraces, suggesting the need for DNAbased studies to show the full extent of the existing diversity. The observed manipulations of wild growing yams in Southwest Ethiopia suggest that yam domestication is still an active process. Knowledge of domestication was shared by 44% of the farmers, even by those that had never practice it. Farmers who have recent transplants in their garden varied from 4% in Bench to 10% in Sheko. The duration of domestication can take up to 6 years, but with most of the individuals it only takes 3 to 5 years. By linking two types of evidences, two divergent adaptation processes are distinguished: (1) parents of recent domesticate expressing a domestication syndrome belongs to wild D. abyssinica or D. praehensilis, and (2) populations of incipient domesticate that might be derived from feral or diverse types of hybrids. A description and analysis of each of these processes and their role on the adaptation process of yams is presented. Based on this account, the term adoptive transplantation is proposed to replace domestication. Although only a few landraces were used, a considerable variability existed in nutritional compositions among the studied samples. The results of nutritional study showed that landraces from D. alata contained high amounts of crude fat and ash contents that make them a good source of energy and minerals. Landraces from the D. cayenensis complex contained low moisture content that makes them suitable for prolonged storage and processing. The variability observed both among different species and among landraces in a single species highlights their potential in future breeding. More generally, this PhD study documented a great wealth of knowledge on distribution, the level of diversity within the yam, the taxonomic status, folk biosystematics and the local management practices. This constitutes an essential step towards setting development priorities and for enhancing the traditional yam farming in the studied areas. This study thus form an important part of an ongoing study aimed at designing an effective collection and conservation strategies for efficient utilization in future yam improvement.