Towards understanding factors that govern fertilizer response in casave: lessons from East Africa

Information on fertilizer response in cassava in Africa is scarce. We conducted a series of on-farm and on-station trials in two consecutive years to quantify yield responses of cassava to mineral fertilizer in Kenya and Uganda and to evaluate factors governing the responses. Average unfertilized yields ranged from 4.2 to 25.7 t ha-1 between sites and years. Mineral fertilizer use increased yields significantly, but response to fertilizer was highly variable (-0.2 to 15.3 t ha-1). Average yield response per kg applied nutrient was 37, 168 and 45 and 106, 482 and 128 kg fresh yield per kg of applied N, P and K, respectively in 2004 and 2005. Fertilizer response was governed by soil fertility, rainfall and weed management, but was not influenced by variety, pest and disease pressure and harvest age. Relative N and K yields were positively correlated to SOC and exchangeable K, while response to fertilizer decreased on more fertile soils. Still, fertilizer response varied widely on low fertility soils (e.g. on soils wit

Influence of spectral properties on cassava leaf development and metabolism

Cassava’s importance as a food security crop in Sub Saharan Africa will be enhanced by its special traits such as tolerance to drought and high yields under hydrothermal stress. Some of the special traits which include the light reflective and absorptive properties of the leaves that depend on the surface characteristics of the leaves, are variety dependent and may influence the plants’ reaction to light; hence, its photosynthetic capacity. We investigated the differences in the leaf spectral properties in different cassava varieties and related them to leaf biochemical properties using 20 cassava varieties established in a randomized complete block design in Kasese, western Uganda. Time dependent changes in leaf spectral characteristics were studied using Digimizer software and related to changes in sugar and pigment properties. Changes in the amount of reflected light were observed for the three main wavelengths used by plants (blue, green and red) with the blue being the most preferred. Total soluble free sugars exhibited a diurnal pattern from lower values (0.07 mg/g) after the dark period to higher values (0.313 mg/g) as the day progressed and was different from those of translocatable sugars such as sucrose. Chlorophyll a exhibited a curved pattern in all varieties increasing with increase in light intensity from 09:00 h (0.18 ug/g), peaking at 15:00 h (0.22 ug/g) and dropping down in concentration by 18:00 h (0.16 ug/g). Significant differences were observed in cassava varieties for the concentration of chlorophylls and carotenes. The results were obtained at a time of optimal growth conditions (four months after planting) and were used to classify these varieties into three broad groups showing that studies on spectral properties of leaves can still give a lot of insights in selection for stress tolerance under less optimal stress. The significant changes observed in the phenotype especially the foliar portion of the plant with the stay green and early recovering mechanisms of tolerance identified also tarried well with observed spectral differences. The results show that studies on plant spectral properties can be important in making inferences on the plants physiological and growth status.Keywords: Spectral properties, tolerance mechanisms, physiology, reflectance

Identification of F1 cassava (Manihot esculenta Crantz) progeny using microsatellite markers and capillary electrophoresis

Generation of genetic diversity is necessary in improving on the potential of cassava when faced with various biotic and abiotic challenges. Presently, cassava breeders are breeding for a number of traits, such as drought tolerance, early root bulking, yield, starch, beta-carotene, protein, dry matter, pest and disease resistance, by relying on genetic diversity that exists in manihot esculenta germplasm. Controlled pollination is one of the main methods used to generate genetic diversity in cassava. However, the process of controlled pollination especially in an open field is prone to contamination by illegitimate pollen right from the time of pollination, seed collection, nursery bed establishment to planting of the trials. Therefore, authentication of the progeny obtained from cas-sava crosses is very important for genetic studies. Twelve informative microsatellite markers were used to verify the authenticity of 364 F1 progeny thought to come from four controlled parental crosses. The transmission of each allele at nine microsatellite loci was tracked from parents to progeny in each of the four Namikonga-derived F1 cassava families. Out of the 364 F1 progeny, 317 (87.1%) were true-to-type, 44 (12.1%) were a product of self-pollination and 3 (0.8%) were a product of open pollination. The consistency of the results obtained using microsatellite markers makes this technique a reliable tool for assessing the purity of progeny generated from cassava crosses

Drug procurement, the Global Fund and misguided competition policies

In an effort to increase competition and decrease price, the Global Fund to Fight AIDS, Tuberculosis and Malaria recently began asking some grant recipients to use international competitive bidding processes for certain drug purchases. Unfortunately, for countries like Kenya, this request has caused more harm than good. After awarding the tender for its annual supply of the anti-malarial artemether-lumefantrine to the lowest bidder, Ajanta Pharma, Kenya experienced wide stock-outs in part due to the company's inability to supply the order in full and on time. Similar problems could arise in Uganda. Despite Kenya's experience, Uganda has awarded its next tender for artemether-lumefantrine to Ajanta Pharma. Uganda is already facing wide stock-outs and risks exacerbating an already dire situation the longer it takes to fulfil the procurement contract. A tender process based primarily on price cannot account for a company's ability to consistently supply sufficient product in time

Oesophageal cancer management guidelines for Uganda

No Abstrac

Patterns of nucleotide diversity in Meisa1 and G3pdh in wild and cultivated cassava

The distribution and frequency of single nucleotide polymorphisms (snps) is an excellent tool for discerning evolutionary relatedness between cultivated and wild plant genomes. This type of information is scanty for the genus Manihot, and thus limiting systematic approaches in the genetic improvement of cassava. Here, we present a detailed description of the comparative patterns of snps in Isoamylase1 (Meisa1) and Glyceraldehyde-3-phosphate dehydrogenase (G3pdh) in 10 accessions of wild (Manihot esculenta subsp. flabellifolia) and 12 accessions of cultivated cassava (M. esculenta). The results show that Meisa1 is more variable in cultivated cassava than that in subspecies flabellifolia, where the 954 bp sequence region differs at 1 in 111 and 250 nucleotides of cultivated and wild species, respectively. Frequency analysis shows that snp occurs once every 42 bp in cultivated and every 70 bp in wild. Tajima’s D test statistics showed that Meisa1 has been evolving under different selection pressures, diversifying in cultivated and purifying in wild. G3pdh is under diversifying selection in both populations. This may indicate the importance for isoamylase1 in starch quality traits in cassava, a trait that is likely to have been the target for artificial selection by farmers and breeders, in addition to natural selection. This study also suggests that G3pdh may be a good marker for phylogeny study while Meisa1 may be useful for intra and inter-cultivar diversity studies. The non-synonymous snps that changed the amino acid property were identified and the potential implication of the change in protein function was analyzed and discussed

Genetic diversity among farmer-preferred cassava landraces in Uganda

Understanding of genetic diversity among a breeding population is an important requirement for crop improvement as it allows for the selection of diverse parental combinations and formation of heterotic pools for genetic gain. This study was carried out to determine genetic diversity within and among 51 farmer-preferred cassava ( Manihot esculenta ) landraces and 15 elite accessions grown in Uganda. Twenty six simple sequence repeat (SSR) markers used for genetic diversity assessment in this study revealed a total of 154 alleles, of which 24% were unique alleles present only in landraces. The genetic diversity and observed herozygosity in landraces were slightly higher than in elite accessions. Elite accessions clustered with some of the landraces indicating that there were some alleles in common. However, 58.8% of the landraces fell into 3 different clusters independent of the elite accessions. Including these landraces with unique alleles in cassava breeding schemes will increase the chances of producing farmer preferred adapted elite cultivars. The study also revealed genetic differentiation among accessions from different regions providing an opportunity for establishment of heterotic pools within a breeding programme.La compr\ue9hension de la diversit\ue9 g\ue9n\ue9tique est une condition importante dans la s\ue9lection de diverses combinaisons parentales et la formation des groupes h\ue9terotiques d\u2019int\ue9r\ueat g\ue9n\ue9tique pour l\u2019am\ue9lioration des cultures. Cette \ue9tude \ue9tait conduite pour d\ue9terminer la diversit\ue9 g\ue9n\ue9tique parmi 51 vari\ue9t\ue9s locales de manioc ( Manihot esculenta ) pr\ue9f\ue9r\ue9es des fermiers et 15 accessions \ue9lites cultiv\ue9es en Ouganda. Vingt six marqueurs simples \ue0 sequence r\ue9p\ue9t\ue9e (SSR) utilis\ue9s pour l\u2019\ue9valuation de la diversit\ue9 g\ue9n\ue9tique ont r\ue9v\ue9l\ue9 un total de 154 all\ue8les, parmi lesquelles 24% \ue9taient des all\ue8les uniques pr\ue9sentes dans les races locales seulement. La diversit\ue9 g\ue9n\ue9tique et l\u2019h\ue9terozygosit\ue9 observ\ue9es dans les races locales \ue9taient l\ue9g\ue8rement sup\ue9rieures que dans les accessions \ue9lites. Celles-ci s\u2019\ue9taient regroup\ue9es avec quelques vari\ue9t\ue9s locales indiquant donc qu\u2019elles avaient quelques all\ue8les en commun. Par ailleurs, 58.8% des races locales ont form\ue9 trois diff\ue9rents groupes ind\ue9pendamment des accessions \ue9lites. Inclure ces races locales \ue0 all\ue8les uniques dans les syst\ue8mes d\u2019am\ue9lioration du manioc permettra d\u2019augmenter les chances de produire des cultivars \ue9lites pr\ue9f\ue9r\ue9s des fermiers. L\u2019\ue9tude montre aussi que la diff\ue9renciation g\ue9n\ue9tique trouv\ue9e parmi les accessions de diff\ue9rentes r\ue9gions est une opportunit\ue9 offerte pour l\u2019\ue9tablissement des groupes h\ue9terotiques dans le programme d\u2019am\ue9lioration