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Articles by Derib Alemu
Total Records ( 2 ) for Derib Alemu
  Haymanot Awgchew , Hailay Gebremedhin , Girma Taddesse and Derib Alemu
  Background and Objective: Potato is an important crop grown by many smallholder farmers in the central part of Ethiopia. However, the productivity of the crop is low which is mainly attributed to poor soil fertility and improper application of fertilizers. Thus, this field experiment was conducted to study influence of nitrogen rate on nitrogen use efficiency and quality of potato (Solanum tuberosum L.) varieties at Debre Berhan, Central Highlands of Ethiopia. Material and Methods: Factorial experiment of six nitrogen rates (0, 46, 92, 138, 184 and 230 kg N ha–1) and two varieties (Gera and Gudene) were arranged in randomized complete block design scheme with three replications. The collected data were subjected to ANOVA using SAS-GLM procedure. Results: The total N uptake and concentration in above ground part were raised by two and three folds, respectively with application of 230 kg N ha–1 that had increased N concentration in tuber by 57.17% and soils after harvest by 20.87% as compared to the control. Generally, the highest values of total dry matter, above ground biomass, total plant dry matter and medium size tubers were found at the 184 kg N ha–1 rate. However, the maximum amounts of agronomic and physiological N efficiencies were recorded at 46 kg N ha–1 that had the highest percent of apparent N recovery and N harvest index. Conclusion: The finding of this study had revealed that N had significant impact on production of quality potato tubers and nitrogen use efficiency. Generally, 184 kg N ha–1 showed the highest dry matter accumulation with good apparent nitrogen recovery and agronomic nitrogen use efficiency, beyond which there were poor efficiency and non-significant difference.
  Derib Alemu , Fikre Lemessa , Mulatu Wakjira and Gezahegn Berecha
  Tomato (Lycopersicon esculentum Mill.) is one of the most widely grown vegetables in the world including Ethiopia. However, its production is constrained by different abiotic and biotic factors. Among biotic factors, bacterial wilt caused by Ralstonia solanacearum is one of the most important pathogens, threatening the production of tomato and potato in Ethiopia. So far there is no single means that would totally manage the disease and provide an absolute cure or fully protect host plants against the pathogen. Hence it is important to look for alternative mechanisms of disease management that can be used as an integrated disease management scheme. This study was, therefore, initiated with the objectives of evaluating the antibacterial activities of aqueous and solvent (acetone and methanol) extracts of five invasive alien species (Eichhorina crassipes, Mimosa diplotricha, Lantana camara and Prosopis juliflora) against R. solanacearum. In vitro antibacterial test was carried out in disc diffusion sensitivity test in a completely randomized design with three replications. It is evident from the result that most of the plant extracts exhibited significant inhibition of the bacterial growth compared with the control. Aqueous extract of E. crassipes provided the highest inhibition zone (26 mm), followed by M. diplotricha (14 mm). After in vitro screening, four promising invasive alien species extracts (aqueous extracts of E. crassipes, M. diplotricha, L. camara and methanolic extract of P. juliflora) with inhibition diameter>10 mm were selected and Minimum Inhibitory Concentration was assessed in vitro. They were also evaluated on tomato plants by applying the botanicals at three time of application (at the time of inoculation and 2-days before and after inoculation). The result of current study revealed that most of the treatment combinations significantly reduced percent disease severity index, but the inhibitory activities of tested plant species were reliant on type of plant species and their application time. More than 91% reduction in percent severity index of bacterial wilt was observed in tomato plants treated with leaf extract of E. crassipes when it was applied at a time of inoculation. The result suggested a need to continue research on invasive alien species extracts and determine their active principles to develop environmentally friendly management approach against bacterial wilt of tomato.
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