Dioscorea Rotundata Research Articles

Contribution of aroma compounds to the antioxidant properties of roasted white yam (Dioscorea rotundata)

BackgroundThe aroma chemistry and the contribution of the aroma compounds to the anti-oxidative properties of roasted yam have yet to be characterized. The growing popularity of roasted yam in regions where they are being consumed calls for a concerted effort to elucidate their aroma chemistry as well as their anti-oxidative properties.ResultsThe aroma compounds in roasted white yam (Dioscorea rotundata) were isolated and identified using static headspace-gas chromatography-mass spectrometry (SH–GC–MS) and gas chromatography–olfactometry (GC–O). In addition, the anti-oxidative activities of the most abundant volatile heterocyclic compounds (2 pyrroles, 4 furans and 3 pyrazines) were evaluated on their inhibitory effect towards the oxidation of hexanal for a period of 30 days. Twenty-nine aroma-active compounds with a flavour dilution (FD) factor range of 2–256 and an array of odour notes were obtained. Among them, the highest odour activities (FD ≥ 128) factors were determined for 2-acetyl furan and 2-acetylpyrrole. Other compounds with significant FD factors ≥ 32 were; 2-methylpyrazine, ethyl furfural, and 5-hydroxy methyl furfural.ConclusionResults of the anti-oxidative activity showed that the pyrroles exhibited the greatest antioxidant activity among all the tested heterocyclic compounds. This was followed by the furans and the pyrazines which had the least antioxidant activity.

Distribution and diversity of viruses infecting yams (Dioscorea spp.) in Cameroon.

Yam (Dioscorea spp.) is an important food crop cultivated for its edible tubers in Cameroon. Surveys were conducted in Cameroon to determine the incidence and severity of yam mosaic disease and associated viruses in 124 yam farms in four agro-ecological zones in 2014 and 2016. Dioscorea rotundata, D. cayenensis, D. alata, D. Dumetorum and D. bulbifera were most frequently detected yam species in the fields. Symptoms of virus disease were observed on 81.5% of the farms surveyed and the disease incidence ranged from 0 to 96.7%, with an overall mean of 26.5%. Mean symptom severity estimated using a numerical rating scale of 1-5, ranged from 2 to 4.1, with an overall mean of 2.6. Representative set of leaf samples collected from farmers' fields were tested for three viruses known to cause yam mosaic disease in West Africa, viz., Yam mosaic virus (YMV), Yam mild mosaic virus (YMMV) and Cucumber mosaic virus (CMV), using multiplex RT-PCR. YMV and YMMV were detected in 220 (37.2%) of the 591 samples tested and 75% of the farms surveyed. None of the samples tested positive to CMV. Phylogenetic analysis based on the coat protein sequencing of 27 YMV isolates clustered these isolates into three phylogenetic groups. This study demonstrated high prevalence of mosaic disease in yam fields and YMV as main causal agent. Knowledge generated in this study will be useful to augment diagnostic tools and yam mosaic disease control with a view to improve on yam production in Cameroon.

Activated Carbon from Yam Peels Modified with Fe3O4 for Removal of 2,4-Dichlorophenoxyacetic Acid in Aqueous Solution

The removal of organic pollutants from water sources can be enhanced using suitable adsorbents. The aim of this research was to study the adsorption capacity and potential reuse of a magnetic adsorbent prepared from agricultural wastes of yam peels (Dioscorea rotundata) for 2,4-dichlorophenoxyacetic (2,4-D) acid removal. The procedure was performed through carbonization and activation at 400 and 500 °C, respectively. Then, the as-prepared activated carbon (AC) was chemically modified using magnetite (Fe3O4) nanoparticles. The AC and magnetic activated carbon (MAC) were characterized and then used for batch adsorption and regeneration tests at different pH, initial concentrations of 2,4-D, and temperature. AC and MAC were showed to have microporous structures with surface areas of 715 and 325 m2/g, respectively. Superparamagnetic behavior was observed for MAC with a saturation magnetization of 6 emu/g. The results from the batch experiments showed higher adsorption capacity at high initial concentration of 2,4-D, low pH, and room temperature. The thermodynamic parameters indicated that the experiments proceeded as exothermic and spontaneous adsorption. Our findings also showed that MAC can be separated from the water medium through a facile magnetic procedure, and from regeneration experiments, MAC showed better results with 60% of its initial adsorption capacity after five cycles. Hence, MAC was found to be a promising alternative adsorbent of pesticides in water.

Isolation of inulin oligomer from white yam tuber (Dioscorea rotundata) for preparation of curcumin-inulin nanoparticles

Research on the isolation of inulin oligomers from white tuber yam (Dioscorea rotundata) for the manufacture of curcumin-inulin nanoparticles has been conducted. The purpose of this study is to find out the results of inulin isolation from white yam (Dioscorea rotundata) as an ingredient in making curcumin-inulin nanoparticles. Based on the results of the isolation, the rendement of inulin obtained was 10.2%. The solubility tests revealed that inulin had 89% solubility and for curcumin-inulin particles, either with 1:2 or 1:3 ratio had the same solubility, i.e., 92 g/mL. The functional groups of inulin were analyzed by FTIR spectrophotometer. The IR spectrum of inulin showed the availability of OH bonds, CH bending, C=C bonds, C-O-C bonds, and C-OH bonds. The IR spectra of curcumin-inulin of 1:2 and 1:3 ratio, on the other hand, indicated the existence of OH bonds, CH bending, carbonyl strain, C-O strain, C-O-C strain, CH3 bending, and H-C=O bond. The morphologies of inulin and curcumin-inulin particles were analyzed using SEM. The surface shape of inulin was semi-spherical, which are different from the morphology of curcumin-inulin particles spreading over a size range of 169-283 nm. With this particle size, the curcumin-inulin particles tend to form nanoparticles.

Yam Cropping System in Cote d’Ivoire: Current Practices and Constraints

Yam is the first food crop in Cote d'Ivoire. It is being cultivated under a traditional technique system with low output. Detailed profiling of the current practices and opportunities for improvement is essential to increase the benefits of yam for food security and income in the country. This study diagnosed the current practices, constraints, and requirements in order to gain insight on the yam cropping system for research and development in Cote d'Ivoire. The surveys were conducted in seven (7) regions in the main yam production area. Groups of 60 producers per region were investigated. Individual surveys were also conducted on-farm, particularly for diagnosing the physical environment and yam-based production systems. As results, yambased production systems are characterized by mixed cropping (cassava, corn and vegetable crops) and/or rotation with various other crops (rice, groundnut, vegetable crops, …). Preferred plots for yam cultivation are forest, savannah or fallow areas. The major constraints in yam cultivation were the effects of environmental stresses, labor scarcity, pest damage, tuber and seed storage difficulties as well as the low market value of yam. The most cultivated yam varieties are Bete-Bete and Florido for Dioscorea alata and Lokpa for Dioscorea rotundata. The cropping system, the species and varieties vary according to the region, the topo sequence and the type of soil. Knowledgebuilding that take into account constraints related to yam cultivation, for each production area, can serve as guidance for variety breeding and cultivation environment redefinition.

Comparative Studies on the Susceptibility of Three Tubers of Dioscorea Species to Dry Rot in Anyigba, Kogi State

Various yam species are cultivated but white yam (Dioscorea rotundata Poir.), water yam (Dioscorea alata L.) and yellow yam (Dioscorea cayenensis Lam.) are among the most cultivated in Nigeria. The Susceptibility of three tubers of Dioscorea species (D. rotundata, D. alata and D. cayenensis) to dry rot pathogens was investigated. Isolation was made from rotted tuber tissues, followed by pathogenicity test and identification of isolates; two fungal species Aspergillus niger and Rhizopus stolonifer were isolated and identified as the major fungi causing yam tuber dry rot in the study area. There was significant difference (P<0.05) in the susceptibility of the various Dioscorea tuber species studied to rot caused by Aspergillus niger [D. rotundata (20mm), D. alata (11mm) and D. cayenensis (3.5mm)] and Rhizopus stolonifer [ D. rotundata (17.5mm), D. alata (10mm) and D. cayenensis (2mm)]. The phytochemical contents of the three tubers of Dioscorea species examined also varied significantly, with the bioactive substances of D. cayenensis and D. alata relatively higher when compared to D. rotundata. Therefore, this research reveals that three metabolites; Saponin, Flavonoid and Tanin constitute the major trait for resistant ability of D. cayanesis and D. alata to dry rot causing pathogen. Therefore, it is necessary that the differences in susceptibility be considered when developing yam barns. Also, researchers should work on genetically improving the susceptible white yam (D. rotundata) which is commonly eaten by millions of Nigerians with a possibility of increasing the quantities of the deficient phytochemicals.

Identification of candidate flowering and sex genes in white Guinea yam (D. rotundata Poir.) by SuperSAGE transcriptome profiling.

Dioecy (distinct male and female individuals) and scarce to non-flowering are common features of cultivated yam (Dioscorea spp.). However, the molecular mechanisms underlying flowering and sex determination in Dioscorea are largely unknown. We conducted SuperSAGE transcriptome profiling of male, female and monoecious individuals to identify flowering and sex-related genes in white Guinea yam (D. rotundata), generating 20,236 unique tags. Of these, 13,901 were represented by a minimum of 10 tags. A total 88 tags were significantly differentially expressed in male, female and monoecious plants, of which 18 corresponded to genes previously implicated in flower development and sex determination in multiple plant species. We validated the SuperSAGE data with quantitative real-time PCR (qRT-PCR)-based analysis of the expression of three candidate genes.We further investigated the flowering patterns of 1938 D. rotundata accessions representing diverse geographical origins over two consecutive years. Over 85% of accessions were either male or non-flowering, less than 15% were female, while monoecious plants were rare. Intensity of flowering varied between male and female plants, with the former flowering more abundantly than the latter. Candidate genes identified in this study can be targeted for further validation and to induce regular flowering in poor to non-flowering cultivars. Findings of the study provide important inputs for further studies aiming to overcome the challenge of flowering in yams and to improve efficiency of yam breeding.

Experimental Verification of Yam (Dioscorea rotundata) Drying with Solar Adsorption Drying

This work evaluates the yam (Dioscorea rotundata) drying performance of solar adsorption drying (SAD) compared to solar drying (SD) and open sun drying (OSD). The evaluation concerns the drying cycle for batches of yam, the effect on vitamin C, color and composition. As SAD can be applied during the night, by using air dehumidified by passing through a bed of silica gel, the cycle time for drying batches of yam can be reduced over 20–25% compared to SD and halved compared to OSD. SAD is thereby most effective during the first nights of drying when the driving force is the highest. Composition was not affected by drying methods but did affect vitamin C content. Vitamin C retention is not significant different for SD and SAD, but with a slight preference for SD. For three yam cultivars (‘Pona’, ‘Lilii’ and ‘Dente’), ‘Lilii’ dried fastest and ‘Dente’ drying slowest. SAD maintained 16 the whitish color of yam better than the other drying methods.

Vine cutting propagation in four varieties of yam (<i>Dioscorea species</i>) using different planting media

This study was conducted over a two-year period (two seasons) to assess the potentials of mini tuber production, through vine cutting propagation on four local varieties of yam (Agbagba, Danisa, Shangari and Alata). Three propagation media used were sandy loamy soil, sandy loamy soil with carbonized rice husk (1:7) and sandy loamy soil with carbonized sawdust (1:7). The set up was a 4 by 3 factorial experiment laid out in a Completely Randomized Design (CRD) with three replicates consisting of 288 excised vines with 24 vines per variety per treatment per replicate. The data obtained (percentage survival of vines, number of rooted vines, vines with shoots, numbers of roots/vine, vines with tubers, and number of tubers/vine and fresh weight of tuber/vine) were subjected to statistical analysis and their means compared. Analysis of variance (ANOVA) revealed high significant differences (P ≤0.01) in percentage survival, number of rooted vines, number of roots/vine, vines with shoots, vines with tubers, number of tubers and fresh weight of tubers among treatments, varieties, and treatment by varieties in the two seasons of the study. Percentage survival of vines and number of vines with tubers/pot were generally higher in all Dioscorea rotundata (agbagba, danisa and shangari) than in Dioscorea alata in both seasons while rooting of vines and fresh weight of tubers/vine were better in Dioscorea alata. Also, sandy loamy soil proved to be the best medium of propagation followed by sandy loamy soil with carbonized rice husk while sandy loamy soil with carbonized saw dust was the least.Keywords: Yams, Vine cuttings, Media, Rooting, Tubers

English

Yam is a promising income source for small producers in the Reconcavo Baiano region. However, few genetic studies have been conducted with this culture. In this sense, the aim of this study was to assess genetic variability among 89 genotypes of yam (Dioscorea rotundata Poir.) collected in four municipalities in Bahia State, Brazil. These were assessed based on eight quantitative descriptors. Data were subjected to descriptive statistics, Spearman's rank correlation, Singh criterion, cluster analysis, principal component analysis and dispersion graph. The tuber weight showed the highest coefficient of variation and correlated positively and significantly with width and length of tuber. The tuber length characteristics contributed most to the genetic divergence. The criterion pseudo-t2 divided 89 genotypes into seven groups, being that groups 4, 5 and 7 showed the highest averages for the production characteristics. The first three principal components explained 69.49% variation and dispersion graph showed partly concordant with UPGMA method. This study revealed the existence of genetic variability of yam, which may be explored in future genetic improvement programs. Key words: Dioscorea rotundata Poir., multivariate methods, plant genetic resources, plant breeding.

Open data kit (ODK) in crop farming: mobile data collection for seed yam tracking in Ibadan, Nigeria

ABSTRACTThe purpose of this paper is to illustrate the importance of applying open-source technologies for mobile-based data collection for real-time tracking of seed yam (Dioscorea rotundata and Dioscorea alata) production. In the past, seed yam data in Nigeria have been predominantly collected using field notebooks, which were subsequently entered into a Microsoft Excel spreadsheet or Access database for analysis and reposition. Relevant areas of weakness within the current data systems include time delay in providing feedback and non-availability of data upon demand. As a result, this has hampered direct tracking of seeds at various stages of crop production and management. The study provided data collectors with a pre-installed yam seed tracking app for use on an Android device for data collection and management. The system architecture is based on the Open Data Kit (ODK) framework and a custom design based on requirements and lessons learned from literature. The ODK (Aggregate) made data easily accessible in minimum time possible from the point of data collection. The yam seed tracking application was developed as a result, which was field tested. The results indicated that this method improved efficiency, speed, and convenience in data collection and visualization, showing that this type of system can be used in crop management and research. The ODK was helpful to farmers in making their management decisions and ultimately boosting crop productivity. Stakeholders were able to visualize trends in yam production, which helps with marketing decisions.

Distribution and virulence of fungal species isolated from yam (Dioscorea spp.) tubers in three agroecological zones of Nigeria

Field surveys were conducted in 2012 and 2013 to evaluate the distribution and virulence of fungal isolates associated with tuber rot disease among yam (Dioscorea spp.) producing agroecological zones (AEZs) of Nigeria. A total of 70 and 66 farmers’ fields were surveyed in 2012 and 2013, respectively among three yam species, Dioscorea rotundata, D. alata and D. cayenensis. Fifteen rotted samples were randomly collected per each yam species in fourteen districts across the humid rainforest (HF), the derived savanna (DS) and the southern Guinea savanna (SGS) agroecologies. Twenty-one fungal species were isolated in the HF, 18 species in the DS and 16 in the SGS. The highest rot severity was in HF agroecology in the D. rotundata which varied from 27.2% to 65.7% in 2012 and from 21.1 to 57.4% in 2013, while the SGS agroecology had the least severity. Lasiodiplodia theobromae was the most virulent pathogen with lesion diameter of 26.8–42.1 mm at 14 days after inoculation. Findings provide baseline information for the formulation of management strategies for yam tuber rot disease in Nigeria.

Enhancing growth and yield of crops with nutrient-enriched organic fertilizer at wet and dry seasons in ensuring climate-smart agriculture

PurposeRapid nutrient depletion in soils is one of the major problems that affect food production and food security in Sub-Saharan Africa. Studies have linked the growth of food crops with seasonal variation and differences in weather conditions. This study was conducted to assess the effects of various organic fertilizer formulations (OFFs) on the growth and yield of selected crops (Zea mays L.; Glycine max, TX 114 and Dioscorea rotundata Poir) during rainy and dry seasons to ensuring climate-smart agriculture.MethodsThe OFFs used were plant-based (PB), animal-based (AB), rock-based (RB), organic mixture (OM-mixture of PB, AB and RB), synthetic/chemical (SC) while ordinary compost without fortification served as control. Effects of OFFs on growth parameters (number of leaves, plant height, stem girth, leaf area, and crop yield) of maize, yam and soybeans were assessed in plot experiments across the two seasons.ResultsThe RB gave highest growth performances in maize and soybean plots at both seasons when applied at 2.5 t ha−1. It also improved yam growth when applied at 2.5 t ha−1 (rainy season) and 3.0 t ha−1 (dry season) more than any other fertilizer. The largest yield of maize in the dry season was obtained from plots with PB at 2.0 t ha−1. The AB at 2.0 t ha−1 gave the largest soybean yield in the rainy season.ConclusionsOrganic fertilizers enriched especially with rock-based and plant-based materials have the potential to ameliorate the threat of climate change and seasonal variation to food security.

English

The antimicrobial activities of Xylopia aethiopica and Syzygium aromaticum extracts on fungi associated with rotting white and water yam was investigated. Diseased and healthy yam species of Dioscorea spp. were obtained from some markets. Fungal isolation was done from the samples using standard procedures. Leaves and fruits of X. aethiopica and S. aromaticum were obtained from the botanical garden, University of Ibadan, Ibadan. Crude aqueous and ethanol extracts of the plants were obtained using standard procedures. After pathogenicity tests, the isolated fungi were cultured on acidified potato dextrose agar (APDA) that were impregnated separately with the leaves and fruits of X. aethiopica and fruits of S. aromaticum extracts at specific concentrations for 10 days. Experimental design was completely randomized design (CRD) with three replicates. Mycelial extension of the fungi was measured daily using a meter rule. Data were subjected to statistical analysis using SAS software. Means separation was done using LSD (DMRT) at P≤0.05. The isolated fungi were identified as Aspergillus niger, Aspergillus fumigatus, and Penicillium chrysogenum. Pathogenicity test showed that the three fungi caused rotting in the yams. Growth inhibition of the fungi was significantly (P≤0.05) higher with ethanol extracts than aqueous extract. Highest mycelial growth inhibitory effect was recorded in the S. aromaticum fruit ethanol extracts on all the organisms. Likewise, X. aethiopica leaf aqueous extract showed high mycelial growth inhibition on A. fumigatus at 50 and 75% concentrations while X. aethiopica fruit ethanol and aqueous extracts was noted to have inhibitory effects on the growth of A. niger and P. chrysogenum at 50 and 75% concentrations respectively. The in vitro result underscores the antifungal abilities of these plant extracts and is also suggestive of their promising potential in vivo. Further works are underway to examine their antimicrobial potentials in the field.   Key words: Dioscorea alata, Dioscorea rotundata, postharvest rot, Syzygium aromaticum, Xylopia Aethiopica.

The Effect of Processing on Ascorbic Acid and Dehydroascorbic Acid in Different Varieties of Yam

The effect of some processing method on the ascorbic acid and dehydroascorbic acid content of two cultivars of yam (Dioscorea rotundata and D. cayenensis) were investigated. The processing method adopted were cooking, frying and roasting. The assay of ascorbic acid in the two cultivars ranged from (5.0 – 9.2 mg / 100 g fresh tissue). The moisture contents of the processed samples ranged from 40-55% for D. rotundata and 48-60% for D.cayenensis except for roasted samples which had a moisture content of 30% for the two cultivars of yam. The pH values were similar in all the varieties examined. The level of ascorbic acid after 0 - 8 days of storage ranged from 5.2 - 7.3 mg / 100 g fresh tissue on a moisture -free basis (mfb). The dehydroascorbic acid content varied from 5.0 - 9.2 mg / 100 g fresh tissue on a moisture- free basis. The retention in ascorbic acid and dehydroascorbic acid of the various treatments ranged from 4.9 - 6.2 mg / 100 g and 5.2 - 8.9 mg / 100 g respectively. Thus, different processing methods has contributed to the loss of ascorbic acid with the highest loss observed when the yam samples were roasted and least loss when they were fried.

Chemical Composition of Essential Oil of Mondia whitei and Antifungal Activities Against Aspergillus flavus and Penicillium sp., The Mold Associated on Yams (Dioscorea rotundata Poir.) Tuber Rot

The aim of this work was to determine the chemical composition of essential oil of roots of Mondia whitei and to evaluate their antifungal potential against Aspergillus flavus and Penicillium sp. Oil was obtained by hydro-distillation and gas chromatography was used to analyze their chemical constituents. The fungi were isolated from post-harvest yams (Dioscorea rotundata) showing typical symptoms of tuber rot. Antifungal activities of the oil were tested in vitro against mycelia growth and conidia germination. In situ test was carried out on healthy yams by application of the oil after (preventive test) and before (curative test) infection with pathogens. Results showed that yield of root Mondia whitei essential oil was 2.57 % and the Menth-1-en-7-al <3-oxo-P-> was found to be the main component. Significant reduction of mycelia growth was obtained with minimal inhibitory concentration (MIC) at 500 μl/l and 525 μl/l respectively for Aspergillus flavus and Penicillium sp. This oil completely inhibited the conidia germination of Penicillium sp. with MIC at 525 μl/l while 65.38 % inhibitory was obtained at 1000 μl/l against Aspergillus flavus. In situ test showed significant reduction of necrosis of yam tuber rot. At 2500 μl/l we obtained 47.41 % and 72 % of necrosis inhibition respectively, for preventive and curative healing for Aspergillus flavus, while for Penicillium sp., we obtained at 2625 μl/l, 31.8 % and 43.07 % of the necrosis inhibition, respectively. This study demonstrated that essential oil from roots of Mondia whitei could be promising alternative for management yam tuber loose induced by mold.

Yam genomics supports West Africa as a major cradle of crop domestication.

While there has been progress in our understanding of the origin and history of agriculture in sub-Saharan Africa, a unified perspective is still lacking on where and how major crops were domesticated in the region. Here, we investigated the domestication of African yam (Dioscorea rotundata), a key crop in early African agriculture. Using whole-genome resequencing and statistical models, we show that cultivated yam was domesticated from a forest species. We infer that the expansion of African yam agriculture started in the Niger River basin. This result, alongside with the origins of African rice and pearl millet, supports the hypothesis that the vicinity of the Niger River was a major cradle of African agriculture.

Disparity in Phenotypic and Genetic Characterization of Lactic Acid Microorganisms Isolated from Spontaneous Fermentation of Yam (Dioscorea rotundata)

Aim: In order to ensure the accurate taxonomic identification of the lactic acid organisms that were previously isolated from spontaneously fermented yam for safety assessment and quality assurance purposes, phenotypic and genetic identification data were compared.&#x0D; Study Design: Using the purposive sampling method, four microorganisms were characterized using molecular methods.&#x0D; Place and Duration of Study: Isolates of lactic acid microorganisms (2 bacterial and 2 fungal organisms) from spontaneously fermented yam in a previous study carried out in May 2016 were genetically identified using molecular methods. &#x0D; Methodology: Genomic DNA extracted from the test lactic acid microorganisms were used as templates in a PCR reaction, then, 16s rRNA and nuclear ribosomal internal transcribed spacer (ITS) genes were amplified for the bacterial and fungal isolates respectively. The polymerase chain reaction (PCR) products were electrophoresed on 2% agarose gel prepared with Tris Borate Ethylenediamintetraacetate (TBE) buffers stained with ethidium bromide. Subsequently, the ladder was used in order to determine the sizes of the corresponding amplicons captured on gel images in comparisons. Moreover, sequences of the PCR products were analyzed and the chromatograms subjected to BLAST (Basic Local Alignment Search Tool) analyses to identify the lactic acid organisms.&#x0D; Results: The 2 bacterial isolates were identified as Bacillus subtilis (MK448227) and Bacillus pumilus (MK446418), on the other hand, the fungal isolates were identified as Aspergillus flavus (MK433604) and Aspergillus niger (MK430926). Discrepancies were observed when phenotypic identification data in an earlier report were compared with the molecular data from the present study. &#x0D; Conclusion: The present results underscore the limitations of phenotypic (biochemical) methods in characterizing organisms, particularly, organisms that may end up being used in food processing. Moreover, this is the first report of the novel organisms reported in the present study and makes further work into the development of starter organisms for the production of amala possible in the near future. In addition, proper identification helps in benchmarking the quality assurance and safety assessment of foods prepared using these organisms.

In vitro Study of Antagonistic Capability of Trichoderma harzianum against Aspergillus niger Isolated from Rotten White Yam (Dioscorea rotundata) Tubers

In vitro antagonistic study using dual culture technique was carried out at Advanced Plant Pathology Laboratory, Federal University of Agriculture, Makurdi, Nigeria to assess the potential capability of Trichoderma harzianum as a biocontrol agent against Aspergillus niger isolated from rotten yam tubers. The test antagonist (T. harzianum) was introduced at three different times (same time with pathogen, two days before the inoculation of the pathogen and two days after the inoculation of the pathogen). The plates were incubated for 192 hours and measurements of mycelial radial growths were recorded at intervals of 24 hours beginning from the third day. The results of in vitro interactions between T. harzianum and A. niger revealed that T. harzianum was able to significantly (P ≤ 0.05) inhibit the growth of A. niger at the three different times of introduction of T. harzianum and this increased with the time of incubation. T. harzianum grew faster than A. niger and produced inhibition zones which completely stopped the growth of A. niger. Mean percentage growth inhibition was found to be highest (77.79%) when T. harzianum was introduced 2 days before inoculation of A. niger followed by introduction of T. harzianum same with A. niger (45.96%). The least percentage growth inhibition (28.47%) was recorded when T. harzianum was introduced 2 days after inoculation of A. niger. In all cases, T. harzianum was observed to be effective at checking the growth of A. niger in vitro and therefore showed the capability for the biological control of the pathogen. It is therefore recommended that for effective in-vitro control of A. niger, T. harzianum should be introduced 2 days before the arrival of A. niger.

Safety of Yam-Derived (Dioscorea rotundata) Foodstuffs-Chips, Flakes and Flour: Effect of Processing and Post-Processing Conditions.

The production of yam-derived (Dioscorea rotundata) foodstuffs is mainly performed by small and medium scale processors that employ old traditional methods. This can lead to differences in quality from processor to processor, and from location to location, with consequent safety concerns. As such, the effects of processing and post-processing phases (i.e., storage, transport, etc.) on the safety of some yam-derived foodstuffs—namely chips, flakes, and flour—has been evaluated, with a focus on bacterial and fungal contamination, aflatoxins, pesticides, and heavy metals (Pb, Ni, Cd and Hg). Yams harvested and processed in Nigeria were screened, being that the country is the largest producer of the tuber, with 70–75% of the world production. Results highlighted no presence of pesticides, however, many samples showed high levels of bacterial and fungal contamination, together with heavy metal concentrations above the recommended safety levels. No trend was observed between the items considered; it was noticed, however, that samples purchased from the markets showed higher contamination levels than those freshly produced, especially regarding bacterial and aflatoxins presence. The processing stage was identified as the most critical, especially drying. Nonetheless, post-processing steps such as storage and handling at the point of sale also contributed for chemical contamination, such as aflatoxin and heavy metals. The results suggested that both the processing and post-processing phases have an impact on the safety of yam chips, flakes, and flour.