Effect of genotype and genotype by environment interaction on total cyanide content, fresh root, and starch yield in farmer-preferred cassava landraces in Tanzania

High starch yield is the most important trait for commercialized cassava starch production. Furthermore, cyanide present in cassava roots poses a health challenge in the use of cassava for food. Cassava genotypes have varying maturity periods that are also environmental dependent. This study aimed at identifying suitable cultivars and optimum time of harvest to maximize starch production across three environments. The study found significant difference between genotypes, locations, harvest period, and all the interactions (P ≤ 0.001) for all traits analyzed. Kiroba recorded high starch yields of 17.4, 12.7, and 8.2 t ha−1 at Chambezi, Amani, and Magadu, respectively. Kilusungu recorded highest cyanide content of 300–400 ppm across all locations but Kiroba recorded highest values of 800 ppm, 15 months after planting at Chambezi. Genotype by environment (GGE) biplot analysis revealed that Kiroba was a superior cultivar in terms of starch yield. Kilusungu recorded highest cyanide content and average starch yield, therefore suitable for use in starch production. The study confirmed effect of genotype and genotype by environment interaction, Kiroba cultivar was superior in terms of starch yield and maximum starch yield was obtained at 9 months after planting. Nyamkagile and Kibandameno had the lowest cyanide content across all environments

Attempts to identify Cassava Brown Streak Virus in western Democratic Republic of Congo

Open Access ArticleRoot necrosis similar to those of the cassava brown streak disease (CBSD) were observed on cassava in western provinces of the Democratic Republic of Congo (DR.Congo) in the early 2000’s. However molecular laboratory diagnosis were not able to detect any causative agent responsible for the attacks, hence, the disease related to these symptoms was named CBSD-like disease. In order to assess the distribution and the incidence of the CBSD-like disease, surveys were carried out in four western provinces, comprising, Kwango and Kwilu, Sud Ubangi, Kinshasa and Kongo Central. CBSD-like disease was observed in all surveyed provinces on the basis of root symptoms because foliar symptoms were different to those of the documented cases of CBSD in other parts of east Africa. CBSD-like disease incidence was high in Kongo Central and Sud Ubangi, exceeding an average of 50 %, but low in Kwango and Kwilu (32.8%) and in Kinshasa (19.1%). During the surveys, cassava leaf samples were collected for lab identification of the causal agent. PCR diagnosis was done on these samples using primers specific for the two known CBSVs. All samples tested negative with no amplification of DNA fragments of the correct size. Thus, further analysis on the causative organism is needed using Next Generation Sequencing (NGS) approaches. NGS approaches will help also to identify the causative organism in other Central Africa countries (Angola, Congo-Brazzaville and Gabon) where such cassava root necrosis have been reported or are suspected

The use of needs assessment methodologies to focus technical interventions in root and tuber crop post-harvest systems: a case study to improve incomes and reduce losses associated with marketing of fresh cassava from rural areas to Dar es Salaam

The Transfer of Needs Assessment Methodologies and Post-Harvest Technologies for Non-Grain Starch Staple Food Crops (NGSS) in sub-Saharan Africa project was initiated in Tanzania in July 1993 as a collaborative venture between the Natural Resources Institute (NRI) and the Tanzania Food and Nutrition Centre (TFNC). The project was funded by the UK Department For International Development (DFID). The main project involved activities in Ghana and Tanzania but this report deals exclusively with activities in Tanzania focusing on the transfer of needs assessment methodologies, the application of needs assessment in identifying post-harvest problems and technical interventions for NGSS and the identification, validation and dissemination of a technology to improve incomes and reduce post-harvest losses associated with marketing of fresh cassava roots from rural production areas to urban markets in Dar es Salaam. In the first stage of the project a range of needs assessment methodologies were successfully validated under field conditions through the mechanism of three case studies, which were carried out in Lake Zone, Tanga Region and Dar es Salaam of Tanzania. Following the case studies, two training in needs assessment workshops were conducted in Tanzania to disseminate needs assessment technologies to key personnel from research organisations and institutes in Tanzania, Mozambique, Uganda, Kenya, Ghana, Rwanda and Ethiopia. The needs assessment case study in Tanga Region highlighted post-harvest problems as a major constraint facing farmers and traders involved in the marketing of fresh cassava to urban areas, and formed the basis for a more detailed study of the marketing system for fresh cassava from rural production areas to urban markets in Dar es Salaam. Semi structured interviews with key stakeholders in the marketing system demonstrated that reductions in quality resulting from poor handling and delays in marketing lead to serious reductions in income throughout the market chain. Farmers and market personnel identified the criteria for a technical intervention to reduce income losses incurred when marketing fresh cassava. After considering various options a simple low cost storage technique for fresh cassava originally developed by the Centro Internacional de Agricultura Tropical (CIAT) and NRI and later modified with DFID RNRRS funds by the NRI and the Ministry of Food and Agriculture (MoFA) in Ghana was selected for validation in Tanzania. Validation exercises in Tanzania demonstrated that low cost fresh cassava root storage technology had the technical and economic potential to alleviate postharvest problems associated with marketing of fresh cassava and improve the incomes of those involved in the cassava market system. In the final stage of the project a flexible dissemination strategy was developed and used to carry out a limited technical dissemination campaign in the major cassava markets in Dares Salaam and selected villages ofKisarawe and Ruf~i Districts in Pwani (Coast) Region, and to promote wider awareness of the technology throughout Tanzania. Needs assessment techniques were used to develop practical approaches for dissemination and two impact assessments (November 1996 and December1997) were carried out to assess effectiveness of dissemination activities and allow for optimisation ofthe strategy. The first impact assessment (November 1996) was used to highlight the strengths and limitations of the initial dissemination strategy, so that a more effective strategy could be developed in collaboration with representatives of the Agricultural Extension Services and key stakeholders in the market system. In December 1997 a second impact assessment was made to assess the effectiveness of the revised dissemination strategy and to highlight any problems. The wider awareness campaign was found to have been effective and a number of expressions of interest had been received from organisations and individuals interested in fresh cassava within Tanzania. A high level of interest and awareness was found in markets and villages where training activities had taken place, but a number of problems were identified which were hampering uptake of the technology. The two main problems were: (a). to be effective the technology needs to be implemented at all points in the market system but individuals were unwilling to take the risk ofbeing the first to use the technology without proof of the economic benefits of the technology; (b). the market system is dominated by a large open type of package called a lumbesa which is not suitable for application of the technology or for transport of cassava but is used for other reasons related to transport charges. To overcome the first difficulty the project team developed a marketing demonstration to provide a practical demonstration of the financial benefits of low cost :fresh cassava root storage technology to potential beneficiaries within the marketing system. The second difficulty was addressed by representatives of various village governments and market co-operatives in collaboration with the TFNCINRI project team. In November of 1997 the village governments of Jaribu and Bungu villages in Rufiji District enacted bylaws to encourage adoption of close packaging for cassava and adoption of the new storage technology. To support this initiative the Agricultural Extension Service in Rufiji District have agreed to integrate the technology into their extension programmes, and in addition the village government in Jaribu has initiated its own training programme in the sub-villages around Jaribu. In December 1997 the village governments of Masaki, Sungwi and Gumba villages in Kisarawe District villages decided to follow the lead taken by villages in Rufiji District and develop bylaws and training programmes to promote uptake ofthe new technology. The Agricultural Extension Service for Kisarawe District have acknowledged the importance of cassava as a source of income generation in the District, and have agreed to integrate the technology into their extension programmes. If co-operation between the various stakeholders is maintained it seems likely that the technology will start to be adopted during 1998. This case study within the main regional Africa project has demonstrated not only that low cost :fresh cassava root storage technology has the technical and economic potential to reduce post-harvest losses and improve incomes, but has also shown that key stakeholders are genuinely interested in adoption of the technology and are willing to co-operate and spend their own funds to promote uptake of the technology. However, for successful uptake of the technology a wider dissemination at both local and national level is required. It is also clear that lack of funds in rural areas could constrain producers and country buyers from adopting this technology. To meet the needs ofthose involved in marketing of fresh cassava throughout Tanzania a sustained campaign of dissemination is required, involving close collaboration between the Agricultural Extension Services, selected NGOs and key stakeholders involved in marketing of fresh cassava from rural areas to various urban centres in Tanzania. A concept note for wider dissemination of low cost fresh cassava root storage technology in Tanzania is included in this report (Appendix 5). The fmdings of this case study have shown that successful adoption of this technology would improve the quality of cassava reaching urban consumers, and contribute to poverty alleviation by improving the income generating potential of marketing of fresh cassava

Characterization of brown streak virus-resistant cassava

Cassava brown streak disease (CBSD) has become a major constraint to cassava production in East and Central Africa. The identification of new sources of CBSD resistance is essential to deploy CBSD mitigation strategies as the disease is progressing westwards to new geographical areas. A stringent infection method based on top cleft grafting combined with precise virus titer quantitation was utilized to screen fourteen cassava cultivars and elite breeding lines. When inoculated with mixed infections of Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), the scions of elite breeding lines KBH 2006/18 and KBH 2006/26 remained symptom-free during a 16-week period of virus graft inoculation, while susceptible varieties displayed typical CBSD infection symptoms at 4 weeks after grafting. The identified CBSD resistance was stable under the co-inoculation of CBSV, UCBSV with cassava geminiviruses (CGMs). Double grafting experiments revealed that transmission of CBSV and UCBSV to CBSD susceptible top scions was delayed when using intermediate scions of elite breeding lines KBH 2006/18 and KBH 2006/26. Nonetheless, comparison of virus systemic movement using scions from KBH2006/18 and a transgenic CBSD resistant 60444 line (60444-Hp9 line) showed that both CBSV and UCBSV move at undetectable levels through the stems. Further, protoplast-based assays of virus titers over time showed that the replication of CBSVs is inhibited in the resistant line KBH2006/18, suggesting that the identified CBSD resistance is at least partially based on inhibition of virus replication. Our molecular characterization of CBSD resistance in cassava offers a robust virus–host system to further investigate the molecular determinants of CBSD resistance

Sequencing wild and cultivated cassava and related species reveals extensive interspecific hybridization and genetic diversity

Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. It was domesticated by native Amazonian peoples through cultivation of the wild progenitor M. esculenta ssp. flabellifolia and is now grown in tropical regions worldwide. Here we provide a high-quality genome assembly for cassava with improved contiguity, linkage, and completeness; almost 97% of genes are anchored to chromosomes. We find that paleotetraploidy in cassava is shared with the related rubber tree Hevea, providing a resource for comparative studies. We also sequence a global collection of 58 Manihot accessions, including cultivated and wild cassava accessions and related species such as Ceará or India rubber (M. glaziovii), and genotype 268 African cassava varieties. We find widespread interspecific admixture, and detect the genetic signature of past cassava breeding programs. As a clonally propagated crop, cassava is especially vulnerable to pathogens and abiotic stresses. This genomic resource will inform future genome-enabled breeding efforts to improve this staple crop

Farmer’s Knowledge on Selection and Conservation of Cassava (Manihot esculenta) Genetic Resources in Tanzania.

Farmers have traditionally depended on their knowledge to cultivate diverse set of crop population for their subsistence. This practice has contributed to high genetic diversity found in farmers’ fields. Occurrence of natural disasters has threaten survival of crop populations and diversity, and thus causing food shortage. Breeding efforts have been targeted to develop crop varieties which can tolerate these natural disasters but there has been poor adoption by farmers. There is a need to understand social and biological factors which farmer base on during selection and maintenance of their genetic resources. There is limited information for researcher’s understanding of factors that farmers considered for landraces selection and conservation. In a view of the above mentioned problems a study was conducted using PRA tools to gather information on conservation of cassava genetic resources. The study found that farmer’s decision on what landrace to plant was what has shaped the diversity. Farmer’s decision comprised of diverse factors from food security, market forces and culinary attributes. The study found that seed (stem cuttings) flow occurs as farmers exchange or buy from local market. These exchanges occur within and outside the village. Most of cassava landraces were indigenous to the place and have been grown for more than 40 years, and only 8.4% were newly introduced. There was considerably loss of landraces due to disease, pest and drought outbreaks. Landrace selection decision was made by both men and women and these decisions on the other hand influenced the diversity of cassava landraces found in farmer’s field. Cultivars like Kiroba, Kibandameno and Msenene were found in every farmer’s field in those particular areas but other cassava landraces differed considerably from one field to another. It is concluded that farmer’s knowledge is useful in conservation of cassava genetic resources for improved livelihood. Therefore farmer’s knowledge should be incorporated in research intervention packages to be able to address specific needs of farmers in a particular area and fasten the adoption process. Keyword: Farmer’s knowledge; Genetic resources; Kiroba, Farmer’s decision making

Does African catfish (Clarias gariepinus) affect rice in integrated rice-fish culture in Lake Victoria Basin, Kenya?

An experiment was conducted for 98 days in the Lake Victoria Basin to investigate the interactions of fish and rice growth performance in rice paddies. The experiment was laid out in a split-plot design, with rice cultivar as the main plot and method of rice-fish culture as the sub-plot. Treatments consisted of two levels of rice-fish culture and three cultivars of rice. Rice cultivars used were; ITA, BR 11 and IR 2793-80-1 obtained from the National Irrigation Board (NIB), Kenya. Clarias gariepinus, (15 ± 0.4 g) were stocked at 6 m-2 and given supplementary diet containing 35% crude protein and 7% lipids at 2× maintenance level. There was significantly less incidence of stem-borers in rice-fish polyculture compared to rice monoculture (P< 0.05). Rice-fish polyculture gave significantly higher rice yield than rice monoculture (453 ± 1.0 gm-2). The seed yield differed significantly (P< 0.05) between the rice cultivars with ITA giving the highest yield followed by IR and BR. There were significant differences in growth performance of C. gariepinus in the treatments (F = 4.518,df = 2, P = 0.014) with best growth recorded in the Fish-ITA and least in Fish-BR. Mean net annualized fish production was highest (3,767 ± 300 Kgha-1yr-1) in the ITA-Fish plots with no statistical differences recorded between BR-Fish and IRFish plots. Fish survival ranged from 79.9 to 82.6 percent in Fish-IR, Fish-BR and Fish-ITA respectively.Key words: African catfish, rice-fish culture, rice yield, fish yield