Abstract:
The cultivated sesame (Sesamum indicum L) is an annual plant of the Pedaliaceae family and is considered as one of the oldest crops cultivated by man, having been grown in the Near East and Africa for over 5,000 years for cooking and medicinal needs. Among the major oil crops grown in Ethiopia, sesame seed has a unique position mainly due to its adaptation to arid and semi-arid low land environments. Yet, the insufficient genetic information of Ethiopian sesame populations hinder the access to useful traits present among adapted landraces. The aim of this study was to characterize various sesame germplasm collections of Ethiopia, which represent genotypes from ten geographic locations (Afar, North-Gonder, North-Shoa, North-Wollo, South-Wollo, Benishangul, Gambella, Oromia, SNNP and Tigray), using agro-morphological and molecular (ISSR and RAPD) markers; and to determine the magnitude of genotype x environment interaction in the improved varieties. The agro-morphological and molecular marker analyses results revealed high genetic divergence in the studied genotypes representing different geographic locations in Ethiopia, suggesting the possibility of using these genotypes in breeding programs. Overall results of diversity analyses indicated that the various sesame genotypes included in the study did not show a correlation with their geographical origins such that genotypes from the same location grouped in different clusters and those from different locations grouped in same cluster with XVII higher genetic distance among accessions of the same region as compared to distance of accessions fromdifferent geographic regions. This was consistent in both morphological and molecular techniques used for measuring genetic distances and clustering. This could perhaps be resulted from the exchange over time, of sesame germplasm among farmers across locations, sesame promotion by the extension system and sesame trades across the regions. In the whole sets of variability analyses, the traits capsules/plant, biomass/plant and thousand seed weight were identified as the most important yield contributing traits which showed a strong positive correlation with seed yield/plant. Hence, these traits should be considered in selection of cultivars for seed yield improvement program in sesame. The results from G x E interaction analyses showed that among the studied traits only seed yield/plant number of capsules/plant and oil content were significantly influenced by G x E interaction. However it was noted that the effect of genotype was predominant for the expression of these traits as compared to the effect of environment G x E interaction. None of the varieties studied was found superior for all the traits in all the environments. The stable genotypes identified for one or more traits should be given due emphasis to exploit maximum yield potential in sesame across diverse agro-ecologies of the Awash valleys and also to use them in future breeding program for developing suitable varieties with wider adaptability. Overall, the studies in this research provide important insights into the populations of sesame in Ethiopia and constitute a set of useful background information that can be used as a basis for future breeding strategy and sesame improvement program.