Development of an efficient plant regeneration protocol for sweet potato (Ipomoea batatas L.) cv. Blesbok

An efficient and reproducible plant regeneration protocol for the South African sweet potato (Ipomoea batatas Lam.) cultivar Blesbok was developed in this study. The effect of different hormone combinations and type of explant on shoot regeneration was evaluated in order to optimize the regeneration protocol. Explants in the form of stem sections, leaf discs, apical shoots and axillary buds derived from in vitro stock plant cultures were cultured on Murashige and Skoog (MS) media supplemented with 36 combinations of naphthalene acetic acid (NAA) (0, 0.01, 0.1, 0.2, 0.5, and 1 mg/L) and 6-benzylaminopurine (BAP) (0, 0.01, 0.1, 0.2, 0.5 and 1 mg/L). The highest percentage of shoot regeneration was obtained when apical shoot explants (31%) and axillary bud explants (22%) were cultivated on MS supplemented with 0.01 mg/L NAA + 1 mg/L BAP. Leaf discs and stem section explants produced highly recalcitrant callus that did not regenerate into shoots in shoot induction medium (SIM). Callus from apical shoots explants cultured on SIM developed into shoots. The shoots rooted readily on root induction medium (RIM) and then in hormone free MS medium. Regenerated plants appeared normal and showed a 100% survival rate when transferred to soil. The regeneration protocol described in this study will be used in a plant transformation protocol to produce transgenic sweet potato with broad virus resistance.Key words: Tissue culture, regeneration, sweet potato, genetic transformation

Single particle flame-combustion studies on solid biomass fuels

Combustion of solid biomass in large scale power generation has been recognized as a key technology for the transition to a decarbonized electricity sector in the UK by 2050. Much of the near-term forecast capacity is likely to be by the conversion of existing coal-fired pulverized fuel plant (DECC, 2012). In such applications, it will be necessary to ensure that the combustion behaviour of the solid biomass fuels is engineered to match, as far as practical, that of the original plant design. While biomass feedstock characteristics vary considerably, one controllable variable for pulverized fuel is the size of the particles.Useful modelling for adaptation and design of boiler plant can be improved with more detailed measurement of the real behaviour of individual particles of the varying fuels. Typical power plant biomass fuels including pine, eucalyptus and willow with particle sizes ranging from up to 3. mm (Van Loo and Koppejan, 2008) and with differing moisture content and aspect ratios were selected for study. Single particles were supported in a water-cooled cover and then exposed above a flame, simulating biomass combustion in a furnace. Measurements of ignition delay, volatile burning time and char burn-out time were undertaken using high speed image capture. Temperatures of the surrounding environment and near to the particle surface were measured with thermocouples and thermometric imaging. Thermo-gravimetric measurements on separate samples complement the single particle measurements as a means of verifying the demarcation between the different stages of combustion and providing kinetic data.Analysis of the data identified correlations between the biomass fundamental characteristics, particle size, and the observed combustion profiles. Empirical expressions for the duration of each combustion stage have been derived. These have been validated with basic modelling including the predicted devolatilisation stage calculated by the FG-Biomass model (Chen et al.,1998)

LES modelling of air and oxy-fuel pulverised coal combustion-Impact on flame properties

Large eddy simulations (LES) are used in a CFD model to simulate air-and oxy-fired pulverised coal combustion in a 0.5 MWth combustion test facility. Simulations are carried out using two different burners, namely, a triple-staged low-NOx wall fired burner and an IFRF Aerodynamically Air-Staged Burner (AASB). Non-gray radiation is considered in order to deal with the spectral nature of absorption and emission by high levels of combustion products in oxy-fuel combustion. Predictions using LES are compared with Reynolds averaged Navier Stokes (RANS) calculations using variants of the k-ε model for turbulence and against available experimental measurements. The results suggest that LES can offer improvements over RANS in predicting recirculation zones and flame properties of the pulverised combustion systems investigated. Flame flickering frequencies from the LES simulations are calculated and validated against available measurements. The work presented demonstrates the potential importance of using LES turbulence models for coal combustion

Pulverised coal/biomass co-fire modelling in a full scale corner-fired boiler

The practice of co-firing biomass in full-scale coal utility plants is gradually increasing. This is mainly because of the benefits associated in reducing the coal based CO2 and biomass based SOx and NOx emissions. Significant numbers of existing coal power stations are suitable for co-firing with small/no changes in the original infrastructures. In order to demonstrate this, combustion modelling of a 300MWe, widely used tangentially fired furnace for pulverised coal has been undertaken in this work. Typical Chinese fuels, Huating coal and wheat straw, were burned at 100% coal and under coal/wheat straw co-firing (up to ≈12.5% on a thermal basis). In the experiments, wheat straw has been handled by the existing coal mills and feeding system to a set of dedicated burners. CFD predications are in good agreement in general with the measured data such as temperature, furnace exit oxygen, unburnt carbon in the ash and NOx emissions

Comparison of RANS and LES turbulence models for predicting air-coal and oxy-coal combustion behaviours

It is commonly accepted that with existing physical sub-models, computational fluid dynamics (CFD) can offer significant insight to the complex combustion systems such as those found in the coal-fired power generation industry. With the growth of computing resources and, in particular, the availability of powerful computer clusters, application of Large Eddy Simulation (LES) emerges as an attractive option in modelling of turbulence combustions in coal-fired furnaces. This paper presents the results from a CFD simulation of the coal combustion processes, under both air-fired and oxy-fired conditions in a 1 MWth industrial combustion test facility. Both Reynolds Averaged Navier–Stokes (RANS) and LES approaches have been employed and the results are compared with each other and with experimental measurements. Advantages of the LES underlining its potential for future industrial applications are addressed. It is shown that validation a CFD model that is based on LES requires more detailed experimental data from well-controlled experimental measurements

Moringa oleifera Extracts Effect on Fusarium solani and Rhizoctonia solani Growth

Aims: An in vitro study was conducted to test the effect of concentration levels of Moringa oleifera leaf and seed extracts in controlling the growth of Rhizoctonia solani and Fusarium solani pathogens. Study Design: The experimental design was a 2*7 factorial laid out in a Completely Randomized Design. Potato Dextrose Agar was amended with Moringa leaf extract and seed extract, and mycelial growth of R. solani and F. solani were measured. Place and Duration of Study: University of Zimbabwe pathology laboratory during 2014/ 2015 season. Methodology: The concentrations levels of 10%, 15%, 20%, 25% and 30% from each extract were used. Distilled water (0%) was used as negative control, whilst 10% copper oxychloride was the positive control. Potato Dextrose Agar was amended with Moringa leaf extract and seed extract, and mycelial growth of R. solani and F. solani were measured.  Results: All extracts showed a significant effect on reducing fungal growth (P=0.05). The higher the extract concentration level, the less the mycelial growth and no mycelial growth occurred on the positive control (10% copper oxychloride). Maximum percentages of inhibition of 45 and 50% was recorded against R. solani using Moringa seed extract at 25 and 30% concentrations, respectively. Both Moringa extracts gave 50% inhibition growth of F. solani at the 30% concentration level. Conclusion: Moringa leaf and seed extracts contain antifungal properties which inhibited growth of R. solani and F. solani. Moringa extract concentration levels influenced the antifungal efficacy of the extracts, with higher concentration levels exhibiting an increased antifungal ability against the test pathogens. The phytochemical analysis of Moringa leaves and seed solvent extracts showed presence of alkaloids, flavonoids, glycosides, tanin and phenolic compounds, terpenoids, etc

Rhizoctonia solani Control in Field Grown Cabbage (Brassica oleracea) Using Moringa oleifera Extracts, Beatrice, Zimbabwe

Aims: To determine the antifungal activity of Moringa oleifera leaf, seed, and bark extracts in suppressing Rhizoctonia solani disease in field grown cabbage (Brassica oleracea). Study Design: The experimental design was a 3 x 3 factorial laid out in a split plot in two blocks with three replications. Place and Duration of Study: Field experiments were carried out in the November 2015 to April 2016 season at Victory Farm in Beatrice, Zimbabwe to evaluate the efficacy of Moringa oleifera leaf, bark and seed aqueous extracts in controlling bottom rot caused by Rhizoctonia solani in cabbages. Methodology: Bottom rot and root rot diseases are mainly caused by soil-borne pathogens such as Rhizoctonia solani. The fungal pathogen was isolated from diseased samples, identified and cultured. Cabbage plants were inoculated with the pathogens 5 weeks after crop emergence.  Three Moringa extract concentrations of 60%, 100%, and 140% were sprayed as foliar applications weekly from week 7 after crop emergence until the week 11 after crop emergence. The antifungal activity for each of the different Moringa extract efficacy was evaluated by recording number of totally defoliated plants once every week for the duration of the study. Results: Moringa extracts were significant in reducing the growth of fungi in cabbages (P = 0.05). The leaf and seed extracts which were not significantly different form each other in their antifungal activity. They both revealed a high level of control of Rhizoctonia solani with indice means of 1.552 and 1.697 respectively. The bark extract with a mean of 2.075 differed significantly from the leaf and seed extract in its antifungal properties (P = 0.05) and had the highest disease mean. Conclusion: Rhizoctonia solani fungi growth on cabbage can be effectively reduced by using either seed or leaf extract sprays. Moringa seed and leaf extracts contain antifungal properties which suppressed R. solani progression in field grown cabbage

Black Rot (Xanthomonas campestris pv. campestris) Control in Field Grown Cabbage (Brassica oleracea var. Sugar Loaf) with Moringa oleifera Extracts

Aims: To evaluate if the antibacterial compounds present in Moringa were significant enough to effect suppressive effect on Xanthomonas campestris pv campestris (black rot) in field grown cabbages (Brassica oleracea), in an open field experiment. Study Design: The experimental design was a 3 x 3 factorial laid out in a split plot in two blocks with three replicates. Place and Duration of Study: Field experiments were carried out for 6 months during the October 2015 to April 2016 season at Victory Farm in Beatrice, Zimbabwe Methodology: Three aqueous Moringa extracts (leaf, bark, and seed) at 3 concentration levels of 60, 100 and 140% were sprayed as foliar applications weekly from 5 weeks after crop emergence in cabbages for the duration of the study. The antibacterial activity for each of the different Moringa plant extracts was evaluated by recording number of totally defoliated plants once every week. Results: The results indicated high significance in antibacterial activity of all the three Moringa extracts as they were able to achieve control of Xanthomonas campestris pv campestris black rot disease at varying levels in the cabbage plants (P < 0.05). The highest inhibition of black rot disease progression was recorded during 8th week after crop emergence with the seed extract recording the least mean leaf defoliation of 2.965 followed by the bark extract (3.312) and lastly leaf extract (3.486). Moringa seed extract had the highest antibacterial activity against the black rot disease in cabbages in this study. Conclusion: Bacterial black rot disease caused by Xanthomonas campestris pv campestris in cabbage can be effectively managed by using either seed, bark, or leaf aqua-based Moringa extract sprays. The 100 and 140% concentration levels were most effective, compared to the 60% concentration level. Further studies need to be carried out to assess if the utilization of the Moringa seed extract as a seed dressing would not increase its antibacterial effects against the test pathogen since it is an important seed borne disease of brassicas and crucifers

Investigations of the transportation characteristics of biomass fuel particles in a horizontal pipeline through CFD modelling and experimental measurement

Recent national and international emission legislations to reduce emissions of carbon dioxide are forcing power generation industries using coal to look at various alternatives, such as biomass and especially by co-firing techniques. Biomass is transported to the burners either mixed with the primary fuel, in general, coal, or used in dedicated pipelines. In both cases, transportation of biomass is difficult due to its composition, size, shape and physical behaviour in comparison to the transportation of coal. This study considers experimental measurements for biomass particle transportation in a pipeline with a transverse elbow and compares the results with those using computation fluid dynamic (CFD) techniques. Various materials: flour, willow, wood, bark and a mixture of flour and willow, have been considered in the present investigation. The experimental work was performed using the dynamic changes in the electrostatic charges of biomass particles in conjunction with correlation signal processing techniques. The CFD simulations were performed by considering the effects of gravity, non-spherical drag (based on estimated shape factor), detailed information of the particle distribution, particle wall collisions and particle–particle interactions. Good quantitative and qualitative agreement was obtained between the CFD simulations and the experimental data. It is concluded that particle–particle interactions are of less importance if the mass loading ratio of particles to air is less than 0.03