28Yam mosaic virus (YMV; genus Potyvirus) is considered to cause the most economically important 29 viral disease of yams (Dioscorea spp.) in West Africa which is the dominant region for yam 30 production globally. 31Yams are a vegetatively propagated crop and the use of virus-free planting material forms an essential 32 component of disease control. Current serological and PCR-based diagnostic methods for YMV are 33 time consuming involving a succession of target detection steps. 34In this study, a novel assay for specific YMV detection is described that is based on isothermal 35 reverse transcription-recombinase polymerase amplification (RT-exoRPA). This test has been shown 36 to be reproducible and able to detect as little as 14 pg/μl of purified RNA obtained from an YMV-37 infected plant, a sensitivity equivalent to that obtained with the reverse transcription-polymerase chain 38 reaction (RT-PCR) in current general use. The RT-exoRPA assay has, however, several advantages 39 over the RT-PCR; positive samples can be detected in less than 30 min, and amplification only 40 requires a single incubation temperature (optimum 37°C). These features make the RT-exoRPA assay 41 a promising candidate for adapting into a field test format to be used by yam breeding programmes or 42 certification laboratories.

Potyviruses (genus Potyvirus; family Potyviridae) are widely distributed and represent one of the most economically important genera of plant viruses. Therefore, their accurate detection is a key factor in developing efficient control strategies. However, this can sometimes be problematic particularly in plant species containing high amounts of polysaccharides and polyphenols such as yam (Dioscorea spp.). Here, we report the development of a reliable, rapid and cost-effective detection method for the two most important potyviruses infecting yam based on reverse transcription-recombinase polymerase amplification (RT-RPA).The developed method, named ‘Direct RT-RPA’, detects each target virus directly from plant leaf extracts prepared with a simple and inexpensive extraction method avoiding laborious extraction of high-quality RNA. Direct RT-RPA enables the detection of virus-positive samples in under 30 min at a single low operation temperature (37 °C) without the need for any expensive instrumentation.The Direct RT-RPA tests constitute robust, accurate, sensitive and quick methods for detection of potyviruses from recalcitrant plant species. The minimal sample preparation requirements and the possibility of storing RPA reagents without cold chain storage, allow Direct RT-RPA to be adopted in minimally equipped laboratories and with potential use in plant clinic laboratories and seed certification facilities worldwide.

A closed-tube reverse transcription loop-mediated isothermal amplification (CT-RT-LAMP) assay was developed for the detection of yam mosaic virus (YMV, genus Potyvirus) infecting yam (Dioscorea spp.). The assay uses a set of six oligonucleotide primers targeting the YMV coat protein region, and the amplification products in YMV-positive samples are visualized by chromogenic detection with SYBR Green I dye. The CT-RT-LAMP assay detected YMV in leaf and tuber tissues of infected plants. The assay is 100 times more sensitive in detecting YMV than standard RT-PCR, while maintaining the same specificity.Electronic supplementary materialThe online version of this article (10.1007/s00705-018-3706-0) contains supplementary material, which is available to authorized users.

Bacterial count in prepared food or water is a key factor in assessing the quality and safety of food. It also reveals the level of hygiene adopted by food handlers in the course of preparation of such foods. This comparative study evaluated the bacteriological quality of food and water consumed in Nsukka, Enugu state, Nigeria, using three bacteria enumeration methods. Data obtained are assumed to reflect the level of personal and environmental hygiene in the study population. Ten types of foods-beans, yam, abacha, okpa, moimoi, pear, cassava foofoo, rice, agidi, and garri-and 10 water samples were evaluated for bacteriological quality, precisely determining the level of coliform contamination, using the most probable number (MPN), lactose fermentation count (LFC), and Escherichia coli count (ECC) methods. Bacterial counts differed significantly (p<0.05) among the various food samples. However, this did not differ significantly in the three methods used for the enumeration of coliforms, suggesting that any of the three methods could be validly used for such studies with confidence. Escherichia coli and Klebsiella pneumoniae were the two major coliforms identified among 98 coliform isolates obtained from the various food samples, of which 78 (79.6%) were assumed to be of human origin on account of their ability to grow at 44 o C. The level of coliform contamination in the food samples from vendors and restaurants (geometric mean count 7.64-9.21; MPN ≥50) were above the accepted 10 4 colony-forming unit/g or MPN ≤10 limits. The results of the study, therefore, call for stringent supervision and implementation of food-safety practices and regular education on food and personal hygiene among food vendors.

Bemisia tabaci (sensu latu) is a group of >40 highly cryptic whitefly species that are of global agricultural importance, both as crop pests and plant-virus vectors. Two devastating cassava diseases in East and Central Africa are spread by abundant populations of one of these species termed Sub-Saharan Africa 1 (SSA1). There is a substantive risk that these whitefly-borne pandemics will continue to spread westwards and disrupt cassava production for millions of smallholder farmers in West Africa. We report here, therefore, the first comprehensive survey of cassava B. tabaci in eastern Nigeria, a West African region likely to be the first affected by the arrival of these whitefly-borne pandemics. We found one haplotype comprising 32 individuals with 100% identical mtCO1 sequence to the East African SSA1 populations (previously termed SSA1-SG1) and 19 mtCO1 haplotypes of Sub-Saharan Africa 3 (SSA3), the latter being the most prevalent and widely distributed B. tabaci species in eastern Nigeria. A more divergent SSA1 mtCO1 sequence (previously termed SSA1-SG5) was also identified in the region, as were mtCO1 sequences identifying the presence of the MED ASL B. tabaci species and Bemisia afer. Although B. tabaci SSA1 was found in eastern Nigeria, they were not present in the high abundances associated with the cassava mosaic (CMD) and cassava brown streak disease (CBSD) pandemics of East and Central Africa. Also, no severe CMD or any CBSD symptoms were found in the region.

Highlights Sequence diversity show lack of geographical association between isolates from Ghana and Nigeria. YMMV isolates from Ghana and Nigeria fall within four of the 11 monophyletic groups. Need for stringent control of germplasm exchange as infection is mainly by infected tubers.

The study evaluates the performance of ginger in media containing different concentrations of growth regulators. Twenty-eight different treatment combinations of benzylaminopurine (BAP) and naphthalene acetic acid (NAA) incorporated into Murashige and Skoog (MS) medium were evaluated for optimal media composition for ginger micropropagation. The combination of 0.05 mgl -1 NAA and 4.0 mgl -1 BAP gave the highest shoot regeneration rate of 4.25. However, this did not differ significantly (p>0.05) from the result (3.38) from 0.05 mgl -1 NAA and 1.0 mgl -1 BAP. Considering the performance of the shoot tip explants in media and the need to lower the cost of micropropagation, the latter combination (0.05 mgl -1 NAA and 1.0 mgl -1 BAP) with 80 percent explant survival, gave an appropriate concentration of growth regulators in media composition for ginger propagation. This combination also supported root development, and perhaps would eliminate the stage of in vitro rooting.

Viruses of the genus Badnavirus (family Caulimoviridae) are double-stranded DNA-reverse transcribing (dsDNA-RT) plant viruses and have emerged as serious pathogens of tropical and temperate crops globally. Endogenous badnaviral sequences are found integrated in the genomes of several economically important plant species. Infection due to activation of replication-competent integrated copies of the genera Badnavirus, Petuvirus and Cavemovirus has been described. Such endogenous badnaviral elements pose challenges to the development of nucleic acid-based diagnostic methods for episomal virus infections and decisions on health certification for international movement of germplasm and seed. One major food security crop affected is yam (Dioscorea spp.). A diverse range of Dioscorea bacilliform viruses (DBVs), and endogenous DBV (eDBV) sequences have been found to be widespread in yams cultivated in West Africa and other parts of the world. This study outlines the development of multiplex PCR-dependent denaturing gradient gel electrophoresis (PCR-DGGE) to assist in the detection and analysis of eDBVs, through the example of analysing yam germplasm from Nigeria and Ghana. Primers targeting the three most prevalent DBV monophyletic species groups in West Africa were designed to improve DGGE resolution of complex eDBV sequence fingerprints. Multiplex PCR-DGGE with the addition of a tailor-made DGGE sequence marker enables rapid comparison of endogenous badnaviral sequence diversity across germplasm, as illustrated in this study for eDBV diversity in yam.