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Bredeson J.V.,University of California at Berkeley | Lyons J.B.,University of California at Berkeley | Prochnik S.E.,U.S. Department of Energy | Wu G.A.,U.S. Department of Energy | And 22 more authors.
Nature Biotechnology | Year: 2016

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. © 2016 Nature America, Inc. All rights reserved. Source


Hillocks R.,University of Greenwich | Maruthi M.,University of Greenwich | Kulembeka H.,Lake Zone Agricultural Research and Development Institute | Jeremiah S.,Lake Zone Agricultural Research and Development Institute | And 10 more authors.
Journal of Phytopathology | Year: 2016

Cassava brown streak disease is endemic to the coastal regions of East Africa, and from around 2004, the disease resurged and became epidemic in the Great Lakes Region, where it continues to spread. In both these areas, cassava brown streak disease (CBSD) leaf symptoms occur at high incidences. However, it is the associated symptom of root rot (necrosis) in the starch-bearing tissues that renders the root unfit for human consumption. Because the extent of root necrosis is not known until the crop is harvested and surveys require destructive sampling, root symptoms are much less frequently assessed than are the above-ground symptoms on the leaves and stems. Surveys were undertaken in selected villages in Tanzania, Kenya, Uganda and Malawi to assess the incidence of CBSD leaf symptoms and the incidence and severity of root symptoms, to estimate the impact of the disease on household food security and on cassava processing. CBSD leaf symptoms were recorded at high incidences (40-90% in individual fields) in all fields visited throughout East Africa, but root necrosis incidence was lower than would be expected from the high incidence of leaf symptoms. Severe root necrosis at high incidence was found only on a few varieties, usually grown to a limited extent. It appears that varieties that are prone to root necrosis are being abandoned in favour of those with a lower propensity to develop root necrosis after infection by the virus. © 2016 Blackwell Verlag GmbH. Source


Seguni Z.,Mikocheni Agricultural Research Institute MARI | Sijaona M.E.,Naliendele Agricultural Research Institute NARI | Shomari S.,Naliendele Agricultural Research Institute NARI
Journal of Applied Entomology | Year: 2013

Cashew (Anacardium occidentale) is an economically important cash crop for many rural households in Tanzania. However, its production is constrained by some insect pests and diseases. As a prerequisite for the development of a more sustainable integrated insect pest and disease management strategy for cashew, information on the biology and ecology of the key insect pests and diseases in a changing environment, and on influencing biotic and abiotic factors, is needed. Surveys were conducted in the major cashew nut-producing areas of Tanzania for two seasons: August to December, 2009, and August to December, 2010. Data on number of infested and infected shoots by key insect pests and diseases, natural enemies and associated farmer practices, namely synthetic pesticide use and intercropping systems, were collected from different subzones within agroecological zones. Our data showed that abundance and diversity of key cashew insect pests and diseases were influenced by agroecological zones and subzones. Intercropping was more commonly practised in the northern than in the southern zone. Agrochemicals were most frequently used in the southern agroecological zone and affected the occurrence of natural enemies, notably the weaver ant that was more abundant in the northern zone. Furthermore, our findings revealed that Helopeltis sp. and the powdery mildew remained the major constraints to cashew nut production in Tanzania. © 2013 Blackwell Verlag GmbH. Source

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