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Arnau G.,CIRAD - Agricultural Research for Development | Bhattacharjee R.,International Institute Of Tropical Agriculture | Sheela M.N.,CIRAD - Agricultural Research for Development | Chair H.,CIRAD - Agricultural Research for Development | And 7 more authors.
PLoS ONE | Year: 2017

Yams (Dioscorea sp.) are staple food crops for millions of people in tropical and subtropical regions. Dioscorea alata, also known as greater yam, is one of the major cultivated species and most widely distributed throughout the tropics. Despite its economic and cultural importance, very little is known about its origin, diversity and genetics. As a consequence, breeding efforts for resistance to its main disease, anthracnose, have been fairly limited. The objective of this study was to contribute to the understanding of D. alata genetic diversity by genotyping 384 accessions from different geographical regions (South Pacific, Asia, Africa and the Caribbean), using 24 microsatellite markers. Diversity structuration was assessed via Principal Coordinate Analysis, UPGMA analysis and the Bayesian approach implemented in STRUCTURE. Our results revealed the existence of a wide genetic diversity and a significant structuring associated with geographic origin, ploidy levels and morpho-agronomic characteristics. Seventeen major groups of genetically close cultivars have been identified, including eleven groups of diploid cultivars, four groups of triploids and two groups of tetraploids. STRUCTURE revealed the existence of six populations in the diploid genetic pool and a few admixed cultivars. These results will be very useful for rationalizing D. alata genetic resources in breeding programs across different regions and for improving germplasm conservation methods. © 2017 Arnau et al.


Legg J.P.,International Institute Of Tropical Agriculture | Lava Kumar P.,International Institute Of Tropical Agriculture | Makeshkumar T.,Central Tuber Crops Research Institute CTCRI | Tripathi L.,International Institute Of Tropical Agriculture | And 4 more authors.
Advances in Virus Research | Year: 2015

Cassava (Manihot esculenta Crantz.) is the most important vegetatively propagated food staple in Africa and a prominent industrial crop in Latin America and Asia. Its vegetative propagation through stem cuttings has many advantages, but deleteriously it means that pathogens are passed from one generation to the next and can easily accumulate, threatening cassava production. Cassava-growing continents are characterized by specific suites of viruses that affect cassava and pose particular threats. Of major concern, causing large and increasing economic impact in Africa and Asia are the cassava mosaic geminiviruses that cause cassava mosaic disease in Africa and Asia and cassava brown streak viruses causing cassava brown streak disease in Africa. Latin America, the center of origin and domestication of the crop, hosts a diverse set of virus species, of which the most economically important give rise to cassava frog skin disease syndrome. Here, we review current knowledge on the biology, epidemiology, and control of the most economically important groups of viruses in relation to both farming and cultural practices. Components of virus control strategies examined include: diagnostics and surveillance, prevention and control of infection using phytosanitation, and control of disease through the breeding and promotion of varieties that inhibit virus replication and/or movement. We highlight areas that need further research attention and conclude by examining the likely future global outlook for virus disease management in cassava. © 2015 Elsevier Inc.


Raj M.,Central Tuber Crops Research Institute CTCRI | Nath V.S.,Central Tuber Crops Research Institute CTCRI | Senthil Sankar M.,Central Tuber Crops Research Institute CTCRI | Jeeva M.L.,Central Tuber Crops Research Institute CTCRI | Hegde V.,Central Tuber Crops Research Institute CTCRI
Archives of Phytopathology and Plant Protection | Year: 2014

The methods employed for DNA extraction from many plants is difficult because of the metabolites that interfere with DNA isolation procedures. We have developed a reliable and efficient method for isolating genomic DNA free from polysaccharide, polyphenols and protein contaminants from Dioscorea spp. The method involves inactivation of contaminant proteins by using CTAB/Proteinase K and precipitation of polysaccharides in the presence of high concentration of salt. The purity of genomic DNA was confirmed by A260/280 and A260/230 ratios calculated from the spectrophotometric readings and further by restriction analysis of the isolated DNA using restriction enzymes Eco RI. The total genomic DNA extracted by the new protocol was used for polymerase chain reaction amplification, RAPD analysis, restriction digestion and pathogen screening. The new protocol can be successfully used for both small- and large-scale preparation of genomic DNA from different tissues of Dioscorea spp. The quarantine of seed tubers and use of pathogen-free tubers for planting is a prerequisite for integrated disease management strategy. The protocol can be used for the isolation of genomic DNA from other crop plants too. © 2013 Taylor & Francis.


Abraham K.,Central Tuber Crops Research Institute CTCRI | Nemorin A.,Center de Cooperation Internationale en Recherche Agronomique pour le Developpement | Lebot V.,British Petroleum | Arnau G.,Center de Cooperation Internationale en Recherche Agronomique pour le Developpement
Genetic Resources and Crop Evolution | Year: 2013

Meiosis in the tetraploid (2n = 80) males of Dioscorea alata L. was investigated for the first time. During metaphase I, the chromosomes were associated mostly in 6-8 quadrivalents and the remaining ones as bivalents with no trivalents or univalents. Anaphase I and subsequent stages of meiosis were normal. The observation of quadrivalents in the tetraploids provides cytological evidence for autotetraploidy. The autotetraploid males and females were highly fertile and they produced viable seeds on artificial pollination. Pollination between diploids (2n = 40) and tetraploids (2n = 80) were also successful via embryo rescue, producing triploid (2n = 60) progenies. The discovery of fertile autotetraploids could initiate polyploidy breeding in D. alata by conventional hybridization for the first time. The reduced number of quadrivalents and the high fertility of the autotetraploids are thought to be the result of partial diploidization of meiosis. The findings also refute the assumption of the allopolyploid origin of D. alata from two putative progenitors. © 2013 Springer Science+Business Media Dordrecht.


Mithra V.S.S.,Central Tuber Crops Research Institute CTCRI | Sreekumar J.,Central Tuber Crops Research Institute CTCRI | Ravindran C.S.,Central Tuber Crops Research Institute CTCRI
Archives of Agronomy and Soil Science | Year: 2013

In this article, a process model (SIMCAS) for simulating the growth of cassava is proposed. Crop phenology was simulated as a function of growing degree days (GDD). New algorithms are used in this model to simulate different components of crop phenology. Branching is simulated as a function of the number of leaves and total dry matter produced. Standard methods were followed to compute solar radiation and photosynthesis. Sensitivity analysis confirmed the importance of canopy size on tuber yield. Algorithms for estimating stress due to a shortage of water, nitrogen and potassium are also included in this model. An attempt was made to predict the final yield under field conditions by multiplying stress values by potential yield. The model was tested under different environments. The tuber yield predicted by this model is in good agreement with the corresponding observed values in most of the cases. Estimation of stress due to a shortage of nitrogen, potassium and water is the key aspect of this model. This information can be used to manage stress and thereby achieve the potential yield. By improving the stress algorithm, this model will serve as a useful tool for achieving maximum cassava yield at optimum input level. © 2013 Copyright Taylor and Francis Group, LLC.

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