Studies of food thickeners in Nigeria for contamination by aflatoxigenic forms of Aspergillus and their detection by PCR

This paper reports the contamination of ready-to-use food thickeners, collected from the South-East geo-political zone in Nigeria, by aflatoxigenic form of Aspergillus species. A total of 150 samples from different open markets were observed for fungal contamination by using serial dilution-spread plate method. Although, Aspergillus, Fusarium and Penicillium were the most frequently isolated fungi, Aspergillus species were found to be the most prevalent in all the samples. Furthermore, Aspergillus flavus and Aspergillus parasiticus produced aflatoxin on yeast extract sucrose (YES) media incubated for 10 to 15 days at 27°C in a CO2 incubator. Aspergillus niger showed no sign of any secondary metabolite on the media, set at similar conditions. Although, light microscopy was used to identify these fungi, based on colony morphology, PCR method was used to confirm genetic variation among the Aspergillus group, using ITS set of primers. Gel electrophoresis of PCR products confirmed the presence of Aspergillus species at an amplification range from 500 to 600 bp in all the samples tested. PCR was found to be a sensitive and a more reliable tool for detection and identification of Aspergillus species in food thickeners as opposed to conventional light microscopy. This is a first kind of mycological survey on the contamination of ready-to-use food thickeners sold in Nigeria.Key words: Aspergillus flavus, Aspergillus parasiticus, aflatoxin, food thickeners, ITS

Do smallholder farmer-led seed systems have the capacity to supply good-quality, fungal-free sorghum seed?

Local seed systems that are developed, managed and maintained by farmers are a fundamental practice in smallholder crop production, supporting more than 80% of farmers in sub-Saharan Africa and feeding more than 70% of its population. The resilience of such systems is under threat from poverty, climate change, drought, increased pests and diseases, over-promotion of modern crop varieties, change of lifestyles and restrictive seed policies. The system continues to be maligned as having inferior quality, yet few studies support this assertion. This study aims to fll this research gap by evaluating 60 sorghum seed samples collected from smallholder farmers in Uzumba-MarambaPfungwe and Chimanimani districts of Zimbabwe. We investigated the efect of farmer-led seed management practices (e.g. seed acquisition and seed storage practices) on farm-derived sorghum seed quality (moisture, germination and fungal incidences). We found farmers using diverse seed sources and seed storage practices. Seeds were typically of good quality in that their storage moisture content was low, their germination was high, and fungal incidences were low. Seed sourced from local markets, non-governmental organizations and other farmers had germination and moisture standards that met the sorghum certifcation standards in Zimbabwe. However, few samples obtained from the relatives and government failed to meet the germination and/or moisture certifcation standards. We detected low incidences of fungi (Aspergillus favus, Aspergillus niger, Curvularia lunata, Fusarium sp. and Penicillium sp.) in sorghum seed samples tested and in particular Fusarium sp., which is the most economic important fungus in sorghum production. We conclude that farmer-led seed systems have the capacity to supply seeds of good quality and recommend that such systems should be recognized and promoted to meet the ever-evolving needs of smallholder farmers in sub-Saharan Africa

PGP potential, abiotic stress tolerance and antifungal activity of <i>Azotobacter</i> strains isolated from paddy soils

322-331Azotobacter strains were isolated by serial dilution method and colonies were viscous, smooth, glistening, and brown to black colour on Jenson’s N-free agar. Morphological and biochemical tests showed characteristic features of Azotobacter. Further, molecular analyses revealed the presence of different Azotobacter species viz., <i style="mso-bidi-font-style: normal">A. armeniacus, A. chroococcum, A. salinestris, A. tropicalis and A. vinelandii. The isolates were tested for their ability of nitrogen fixation, indole acetic acid (IAA), gibberllic acid production and phosphate solubilization. Four isolates (GVT-1, GVT-2 KOP-11 and SND-4) were efficient in fixation of highest amount of N2 (29.21 μg NmL-1day-1), produced IAA (25.50 µg mL-1), gibberllic acid (17.25 μg 25 mL-1) and formed larger P solubilizing zone (13.4 mm). Some of the Azotobacter strains were produced siderophores, hydrogen cyanide and were positive for ammonia production with respect to antifungal activity of <i style="mso-bidi-font-style: normal">Azotobacter was tested with dual culture method and A. tropicalis inhibited the growth of Fusarium, Aspergillus and Alternaria species. <i style="mso-bidi-font-style: normal">Azotobacter isolates were tested against salt (0-10%), temperature (4-55ºC), pH (5.0-10) and insecticide chloropyrifos (0-3%) tolerance study. Among them, A. chroococcum was found tolerant to a maximum of 6% NaCl with a temperature of 35-45ºC and to a pH up to 8. All the 4 strains showed effective growth against 3% chloropyrifos concentration. The studies revealed that the Azotobacter strains not only produced plant growth promoting substances but are also tolerant to abiotic stresses such as temperature, pH and insecticides.</span