Rate of re-infection of tissue culture-derived Latin American and East and Southern African cassava genotypes by mosaic disease

The rate of reinfection by cassava mosaic disease (CMD) in initially virus-free cassava plants of two Latin American and twelve East and Southern African cassava genotypes grown was studied under high disease pressure conditions. An improved clone, TMS 4(2)1425, from the International Institute of Tropical Agriculture was used as check. The virus-free plants had been produced through meristem-tip culture and multiplied in a pest-proof screen house. The genotypes were planted in single row plots of 5 plants each, arranged in a randomized complete block design with 4 replications and spacing of 1 × 1 m2. Incidence and severity of CMD on the genotypes were assessed weekly, from 4 to 16 weeks after planting (WAP). Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) tests for the cassava mosaic virus were carried out using young leaves collected randomly at 15, 16 and 17 WAP from plants both with and without symptoms. Six genotypes had > 60% CMD incidence at 4 WAP; by 7 WAP, 12 genotypes had > 60% incidence. Only Kigoma red, Kiroba, and UKG-41-6 were notinfected at 4 WAP while Mbudumali had 90% incidence at this time. At 16 WAP, ten genotypes had 100% CMD incidence; Kigoma Red was 39.6% infected. ELISA detected a mean CMD reinfection rate of 66.6%; PCR detected 69%. A high negative and significant (P< 0.01) correlation (r = - 0.70) was established between CMD severity and storage root yield.Keywords: Virus-free cassava genotypes, tissue culture, rate of reinfection, cassava mosaic diseas

A PRISMA-driven systematic mapping study on system assurance weakeners

Context: An assurance case is a structured hierarchy of claims aiming at demonstrating that a given mission-critical system supports specific requirements (e.g., safety, security, privacy). The presence of assurance weakeners (i.e., assurance deficits, logical fallacies) in assurance cases reflects insufficient evidence, knowledge, or gaps in reasoning. These weakeners can undermine confidence in assurance arguments, potentially hindering the verification of mission-critical system capabilities. Objectives: As a stepping stone for future research on assurance weakeners, we aim to initiate the first comprehensive systematic mapping study on this subject. Methods: We followed the well-established PRISMA 2020 and SEGRESS guidelines to conduct our systematic mapping study. We searched for primary studies in five digital libraries and focused on the 2012-2023 publication year range. Our selection criteria focused on studies addressing assurance weakeners at the modeling level, resulting in the inclusion of 39 primary studies in our systematic review. Results: Our systematic mapping study reports a taxonomy (map) that provides a uniform categorization of assurance weakeners and approaches proposed to manage them at the modeling level. Conclusion: Our study findings suggest that the SACM (Structured Assurance Case Metamodel) -- a standard specified by the OMG (Object Management Group) -- may be the best specification to capture structured arguments and reason about their potential assurance weakeners

Epidemiological analysis of yam mosaic virus (YMV) infection risk factors and its implications for clean seed yam systems

Yam mosaic virus (YMV) is a major threat to yam production in West Africa. This study determined factors contributing to the spread of YMV in yam fields, including the role of aphid vectors, seed-borne infections, YMV inoculum in the fields, weather, genetic diversity of the virus, and spatial distance between infected sources. The findings of this study are useful for refining YMV control measures, developing a model for disease risk assessment under different scenarios, and guiding clean seed yam production systems

Crude Oil-Degradation and Plasmid Profile of Nitrifying Bacteria Isolated from Oil-Impacted Mangrove Sediment in the Niger Delta of Nigeria

The crude oil degradability and plasmid profile of autotrophic nitrifying bacteria, Nitrosomonas and Nitrobacter species, isolated from mangrove sediment in the Niger Delta of Nigeria were studied. The effects of temperature, pH and optical density on the utilization of different carbon sources by the bacteria were also investigated. Results showed that nitrifying bacteria could utilize kerosene, diesel oil, jet fuel and engine oil as carbon sources. None utilized hexane and xylene but moderate growth was observed in benzene, phenol and toluene. However, their ability to utilized crude oil varied both in rates of utilization and in growth profiles. Mixed culture of the isolates degrades 52 % of crude oil introduced into the medium followed by Nitrosomonas sp. with 40 % degradation. The least was Nitrobacter sp. with 20 % degradation. The ability of the autotrophs to degrade crude oil was found to be plasmid-mediated through curing experiment and electrophoresis. The size of the plasmid involved was estimated to be 23 kb. The high crude oil utilization of the mixed culture implies that nitrifying bacteria isolated from contaminated ecosystem are excellent crude oil degraders and can be harnessed for bioremediation purposes

Undergraduate students’ perception and Utilization of electronic information resources and services in the university of Calabar library, Calabar, Nigeria

An evaluation of undergraduate students’ perception and utilization of electronic information resources and services was carried out. The population of the study consisted of all registered library users in the 2014/2015 academic session. The total population of the study was 4, 211 registered users. Accidental sampling technique was used to select 300 respondents who constituted the sample of the study. The study relied on questionnaire as the instrument for data collection. The data generated were analysed using descriptive statistics (simple percentage %). The study found that the adoption and utilization of directional signs to guide users to the various divisions and units in the library has proven to be a good publicity variable, as a greater percentage of the respondents (30.3%) admitted that they became aware of the electronic library through directional signs. The finding revealed that 25.6% of the respondents became aware of the availability of e-library resources and services during orientation programme for fresh students. On the perception of electronic resources and services by undergraduate students’ the finding revealed a mix of positive and negative perception. For example, 99 respondents (33%) regard electronic resources and services as difficult to use while 73 respondents (24.3%) perceived eresources as time friendly. It was revealed that the elibrary in the university of calaber is significantly utilized. 23% of the respondents used it daily and 24.7% spent an average of 4-5 hours daily in the elibrary. The study also revealed key factors considered to be inhibitors to the use of electronic resources and services in the University of Calabar as slow speed of Internet browsing service ranked first, (30.7%), followed by inadequate number of computers, (24.7%), poor attitude of library staff (13.3%) and lack of user education, (13.3%).. As more people became aware of the availability of the e -library, the number of users c ontinued to increase therefore putting more pressure on the existing facilities. There is need to increase the number of computers in the e -library to accommodate more users . This would avoid the crowd created outside the e -library by potential users waiting for the opportunity to use the library. Key Words: Undergraduate, students, Perception, Utilization, Electronic, Resources, Electronic Information, Services

Yam breeding

Yams (Dioscorea species of family Dioscoreaceae) are important for food, income, and sociocultural activities especially in West and Central Africa and account for about 93% of the world’s annual production of 38 million tonnes. Breeding of yams is focused primarily on the two dominant species, D. rotundata Poir. and D. alata L., and it is carried out within the context of improving yam-based systems. Constraints to productivity of cultivation and opportunities for improvement are identifi ed through reviews of existing information, new surveys, or stakeholders’ meetings. Hence the principal objectives for breeding include high and stable tuber yield, resistance to pests (e.g., nematodes) and diseases (e.g., viruses, anthracnose), as well as tuber characteristics (shape, food quality) desired by consumers. Viruses are of particular concern in yam research and development because they impose a double limitation in the form of reduced fi eld performance as well as restricted international exchange of germplasm. Of the several viruses infecting yams, the most commonly occurring in West Africa is the Yam mosaic virus (YMV), genus Potyvirus. Field and screenhouse evaluation of Dioscorea germplasm held at IITA has resulted in the identifi cation of high levels of resistance to the virus in Dioscorea landrace cultivars. The inheritance of resistance to the virus in D. rotundata has been established through positive screening of populations at the seminal and clonal stages. These sources form the basis for population improvement towards the development of new yam varieties with higher levels of virus resistance

An overview of viruses infecting Dioscorea yams in subSaharan Africa

Viruses of the genera Potyvirus, Potexvirus, Badnavirus, Cucumovirus, and Carlavirus infect yams of different species worldwide. These viruses cause a range of symptoms including mosaics, mottle, vein clearing, chlorosis, stunting, and distortion. These lead to a chronic and sometimes severe disease situation in all yam growing areas. In sub-Saharan Africa, where more than 90% of the world’s yams are produced, Yam mosaic virus (YMV), genus Potyvirus is an ubiquitous pathogen. It is the only wellcharacterized virus infecting yams. Other viruses infecting yams in sub-Saharan Africa are Dioscorea alata virus (DAV), genus Potyvirus; Dioscorea alata bacilliform virus (DaBV), genus Badnavirus; Cucumber mosaic virus (CMV), genus Cucumovirus; and Dioscorea dumetorum virus (DdV), genus Potyvirus. Dioscorea mottle virus (DMoV), a possible member of the genus Comovirus, was recently isolated from Dioscorea alata in Nigeria. Transmission studies show that YMV, DAV, DaBV, and CMV are mechanically transmissible between yam plants. All these viruses are transmitted by aphids, except DaBV, which is transmitted by mealybugs (Planococcus citri). Although tuber yield losses have been attributed to virus infection, the infl uence of these viruses on yield and growth of the yam plant has not been well studied. Tremendous improvement has been achieved in the detection of yam viruses with the development of highly sensitive and more specifi c diagnostic techniques such as enzyme-linked immunosorbent assays (ELISA), immunosorbent electron microscopy (ISEM), and polymerase chain reaction (PCR). The reliability of these diagnostic tools has enabled the production of virus-tested in-vitro germplasm which can be safely distributed internationally

Evaluation of water yam (Dioscorea alata L.) germplasm for reaction to yam anthracnose and virus diseases and their effect on yield

Use of genetic resistance is the most practical and economic way to manage major diseases of yams. In a search for sources of resistance, 40 water yam (Dioscorea alata L.) accessions from Benin, Ghana, Nigeria and Puerto Rico were screened under natural disease infection conditions in Ibadan, Nigeria. The accessions were evaluated at 1, 3 and 6 months after planting (MAP) for severity of yam anthracnose and viral diseases. The effect of the pathogens on yield was also evaluated at harvest 9 MAP. There were significant differences (P < 0.001) between accessions for severities of anthracnose and viral diseases. Eight (20%) of them had lower anthracnose area under disease progress curves (AUDPC) values than the resistant check while 10 (25%) had AUDPC values below the trial mean. There were significant variations (P < 0.001) in yield components among the accessions. There was significant negative correlation of anthracnose severity with fresh tuber yield (r = −0.51) and with number of tubers per plot (r = −0.40). Similarly, significant negative correlations were observed of virus disease severity with fresh tuber yield (r = −0.78) and number of tubers per plot (r = −0.65). Linear regression models also showed that the fresh yield had significant negative relationships with anthracnose (R2 = 0.26) and viral (R2 = 0.62) diseases. The accessions identified as resistant constitute a valuable resource for breeding of resistant germplasm