Nondegenerate two-photon lasing in a single quantum dot

We propose two-mode two-photon microlaser using a single semiconductor quantum dot grown inside a two-mode microcavity. We explore both incoherent and coherent pumping at low temperatures to achieve suitable conditions for two-mode two-photon lasing. The two-mode two-photon stimulated emission is strongly suppressed but the single-photon stimulated emission is enhanced by exciton-phonon interactions. In coherently pumped quantum dot one can achieve large two-mode two-photon lasing where single-photon lasing is almost absent. We also discuss generation of steady state two-mode entangled state using two-photon resonant pumping.Comment: 12 pages, 13 figure

Morphological and molecular characterisation of Scutellonema species from yam (Dioscorea spp.) and a key to the species of the genus

The yam nematode, Scutellonema bradys, is a major threat to yam (Dioscorea spp.) production across yam-growing regions. In West Africa, this species cohabits with many morphologically similar congeners and, consequently, its accurate diagnosis is essential for control and for monitoring its movement. In the present study, 46 Scutellonema populations collected from yam rhizosphere and yam tubers in different agro-ecological zones in Ghana and Nigeria were characterised by their morphological features and by sequencing of the D2-D3 region of the 28S rDNA gene and the mitochondrial COI genes. Molecular phylogeny, molecular species delimitation and morphology revealed S. bradys, S. cavenessi, S. clathricaudatum and three undescribed species from yam rhizosphere. Only S. bradys was identified from yam tuber tissue, however. For barcoding and identifying Scutellonema spp., the most suitable marker used was the COI gene. Additionally, 99 new Scutellonema sequences were generated using populations obtained also from banana, carrot, maize and tomato, including the first for S. paralabiatum and S. clathricaudatum, enabling the development of a dichotomous key for identification of Scutellonema spp. The implications of these results are discussed

Taro in West Africa: Status, Challenges, and Opportunities

Taro is an ancient nutritional and medicinal crop woven into the fabric of the socio-economic life of those living in the tropics and sub-tropics. However, West Africa (WA), which has been a major producer of the crop for several decades, is experiencing a significant decline in production as a result of taro leaf blight (TLB), a disease caused by Phytophthora colocasiae Raciborski. A lack of research on taro in WA means that available innovative technologies have not been fully utilized to provide solutions to inherent challenges and enhance the status of the crop. Improvement through plant breeding remains the most economically and environmentally sustainable means of increasing the productivity of taro in WA. With this review, we provide insights into the importance of the taro crop in WA, evaluate taro research to date, and suggest how to address research gaps in order to promote taro sustainability in the region

Rolling circle amplification to screen yam germplasm for badnavirus infections and to amplify and characterise novel badnavirus genomes

Since the first discovery of badnaviruses (family Caulimoviridae, genus Badnavirus) in yam (Dioscorea spp.) germplasm in the 1970s (Harrison and Roberts, 1973), several hundred partial badnavirus reverse transcriptase (RT)-ribonuclease H (RNaseH) sequences have been characterised (Kenyon et al., 2008; Bousalem et al., 2009), but only a few complete Dioscorea bacilliform virus (DBV) genome sequences have been reported (Phillips et al., 1999; Seal and Muller, 2007; Bömer et al., 2016 and 2017; Sukal et al., 2017; Umber et al., 2017). We have optimised a workflow involving total nucleic acid extractions and rolling circle amplification (RCA) combined with restriction enzyme analysis for the detection and amplification of DBVs present in yam germplasm. We have employed this approach successfully revealing three novel episomal yam badnaviruses (Bömer et al., 2016). We proposed this to be a complementary method to denaturing gradient gel electrophoresis, which enables a rapid indication of badnavirus diversity as well as the identification of potentially integrated badnavirus sequences in the host genome (Turaki et al., 2017). Here, we describe the step-by-step protocol to screen yam germplasm for badnavirus infections using RCA as an efficient research tool in the amplification and characterization of novel badnavirus genomes

Distribution, incidence and severity of viral diseases of yam (Dioscorea spp.) in Côte d’Ivoire

A survey was conducted in major yam cultivation zones in Côte d’Ivoire in 2009 to determine the incidence, severity of viral diseases, and viruses associated with the infected plants. Incidence and severity of the viral diseases were estimated based on symptoms. Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR)-based techniques were used for the detection of Yam mosaic virus (YMV), Cucumber mosaic virus (CMV), Dioscorea mottle virus (DMoV) and yam badnaviruses in the sampled yam leaves. Disease incidence varied from 0 to 90% and symptom severity from 1 to 5. There were significant difference in incidence and severity between different agro-ecological zones (P < 0.001). About 36% of the samples tested positive to YMV, ca. 1.5% tested positive to CMV, ca. 39.1% samples tested positive to yam infecting badnaviruses, and none of the samples tested positive to DMoV. This study demonstrated high incidence of virus diseases in all the yam production regions and warrants implementation of virus disease control measures.Keywords: Yam, enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), viruses, Côte d’IvoireAfrican Journal of Biotechnology, Vol. 13(3), pp. 465-470, 15 January, 201

Characterization of cucumber mosaic virus isolated from yam (Dioscorea spp.) in West Africa

Millions of people in the West African sub-region depend on yam for food and income. In 2008, cucumber mosaic virus (CMV), one of the most economically important plant viruses was detected in yam fields in Ghana, Benin and Togo, three of the five topmost yam producing countries in the world. Some strains of CMV are reportedly more virulent than others thus the need to characterise the strain isolated from yam. Sap inoculation of the yam strain induced systemic mosaic on Cucumis sativus and systemic chlorosis, necrotic lesions and leaf distortion on Nicotiana glutinosa. Sequence analysis of the 3' end of the coat protein gene and C-terminal noncoding region revealed 98 to 99, 93 to 98 and 78 to 79% nucleotide homology with members of the subgroups IA, IB and II, respectively. This analysis further revealed the absence of the EcoR1 restriction site characteristic of subgroup II strains and the presence of 15 nucleotide deletions dispersed along the C-terminal noncoding region of subgroup IA strains. At the amino acid level, the virus had 99 to 100% homology with subgroup I strains and 89% homology with subgroup II strains. Phylogenetic analysis of the amino acid confirms that the yam strain of CMV belongs to subgroup I while nucleotide sequence phylogeny confirms its placement in subgroup IA.Keywords: Yam viruses, cucumber mosaic virus, sequence analysisAfrican Journal of Biotechnology Vol. 12(22), pp. 3472-348

A study of the M235T variant of the angiotensinogen gene and hypertension in a sample population of Calabar and Uyo, Nigeria

AbstractA common molecular variant of the angiotensinogen gene had been reported to predispose some ethnic groups to hypertension. This case–control study was designed to determine the frequency and association of the angiotensinogen M235T allele with hypertension in residents of Calabar and Uyo cities, south–south Nigeria.The study involved 1308 subjects, 612 patients and 696 controls. The M235T variant was investigated using an allele specific polymerase chain reaction and enzymatic digestion to determine allele frequencies. Hypertensinogenic factors such as dietary habits, physical activity, smoking and drinking habits were assessed using questionnaires. Descriptive statistics, chi-square and multiple regression analysis were used to analyze the data obtained.The M235T allele frequency was high (0.94 for hypertensives and 0.96 for controls) though it was not associated with hypertension status. The odds ratio for hypertension was 0.64 (95% confidence interval: 0.39–1.06) there were no significant differences between the genotype frequency of hypertensives and controls. By multiple regression, Hypertension was observed to be associated with age and was a predictor for systolic blood pressure in both patient r2=0.359; p<0.05 and control groups r2=0.26.Age and body mass index were predictors for diastolic blood pressure in the control group, r2=0.28.Although the frequency of the M235T variant was high, it was not a significant risk factor for hypertension in the study population

Biological and biochemical characterization of isolates of Helicoverpa armigera Nucleopolyhedrovirus [HaNPV] from different geographic locations of India

Six strains of HaNPV collected from different places of India were compared for their biological and biochemical characteristics. Based on the bioassay tests against second and third instar larvae of Helicoverpa armigera the order of activity in increasing order is UASD-HaNPV< AK-HaNPV<TN-HaNPV<PAU-HaNPV<GAUHaNPV< ICRISAT-HaNPV and no correlation was drawn between biological and biochemical characteristics. Electron microscopic observations of polyhedra, alkali disrupted polyhedra during purification and nucleocapsids are also presented