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

A comparative study of the physicochemical properties of starches from root, tuber and cereal crops

Some properties of starches from cassava, potato and sweet potato were compared with cereal starches from maize, wheat, millet and sorghum. The aim was to determine the properties of tuber and root crop starches and compare them with cereal starches in addition to unravelling the potential of commonly grown sorghum and millet climate resilient crops as cheap and sustainable sources of starch. Significant variations were observed for amylose content and solution properties of starches, where blue values for amylose ranged from 0.355 in potato to 0.476 in cassava, but were averagely low in cereal starches. Amylose leaching increased with temperature with the highest value (0.432) in cassava at 80°C compared with cereal starches (average 0.361). Starch amylosis increased with time of hydrolysis and was highest (>16%) for millet and sorghum and least for potato (<8.5% average). Average swelling power at 80°C was high for cassava (8.58 g/g) and potato (8.44 g/g) compared with sweet potato (6.88 g/g) and low among cereal starches (5.17 g/g). Similarly, starch solubility was low in potato (0.77 g/g) and sweet potato (0.577 g/g) compared with cassava (1.23 g/g). The paste clarity was also high for cassava (48.32%) and potato (42.16%) and least for sweet potato derived starches (23.22%) and all the cereal starches (14.97%). These properties demonstrate the untapped potential of cassava and tuber based starches for use in food and non-food applications previously dominated by cereal starches.Key words: Tuber starch, root crop starches, cereal starches, amylose, amylosis

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

Effect of self-pollination with heat-treated pollen on parthenocarpy and homozygosity in cassava

Cassava\u2019s ( Manihot esculenta Crantz) high heterozygosity complicates its genetic improvement via selective breeding. Double haploid (DH) technology can be used to improve the crop\u2019s heterozygosity, thereby improving the capacity for genetic improvement. The objective of this study was to evaluate the effect of self-pollination using heated pollen on pollen tube penetration, fruit set, seed and haploid embryo development in cassava genotypes for the production of haploid cassava. Pollen from two cassava genotypes, NASE3 and NASE14, was heated at 40, 50 and 60 oC for 0.5, 1.0 and 2.0 hr each. The heated pollen was used in six rounds of self-pollinations. Pollen tube penetration was monitored by fluorescent microscopy, followed by early embryo rescue and ovule culture. Ploidy and zygosity were assessed using flow cytometry and single-nucleotide polymorphism analysis, respectively. Pollen germinated on the stigma, grew within the style through the nucellar beak, but did not reach the embryo sac, thus achieving no fertilisation in all the 5756 self-pollinated flowers. There was a reduction in pollen germination (in vitro and in vivo), pollen tube penetration and fruit set with increasing temperature. Heat-treated pollen stimulated division of the egg cell and induced development of parthenocarpic fruits. Up to 6 embryoids per ovule were observed and all regenerated plantlets were diploid, with up to 93.0% increased homozygosity. For the first time, plant regeneration from ovules, pollinated with fresh pollen at 14 days after pollination, was achieved indicating improved speed in plant regeneration. The data generated are important for the development of protocols for cassava DH plant production.La forte h\ue9t\ue9rozygotie du manioc ( Manihot esculenta Crantz) complique son am\ue9lioration g\ue9n\ue9tique par s\ue9lection s\ue9lective. La technologie d\u2018 haplo\uefde double (DH) peut \ueatre utilis\ue9e pour am\ue9liorer l\u2019h\ue9t\ue9rozygotie de la culture, am\ue9liorant ainsi la capacit\ue9 d\u2019am\ue9lioration g\ue9n\ue9tique. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer l\u2019effet de l\u2019auto-pollinisation \ue0 l\u2019aide de pollen chauff\ue9 sur la p\ue9n\ue9tration du tube pollinique, la nouaison, le d\ue9veloppement des graines et des embryons haplo\uefdes dans les g\ue9notypes de manioc pour la production de manioc haplo\uefde. Le pollen de deux g\ue9notypes de manioc, NASE3 et NASE14, a \ue9t\ue9 chauff\ue9 \ue0 40, 50 et 60 oC pendant 0,5, 1,0 et 2,0 heure (s) chacun. Le pollen chauff\ue9 a \ue9t\ue9 utilis\ue9 dans six cycles d\u2019auto-pollinisation. La p\ue9n\ue9tration du tube pollinique a \ue9t\ue9 surveill\ue9e par microscopie fluorescente, suivie d\u2019un sauvetage pr\ue9coce des embryons et d\u2019une culture d\u2019ovules. La plo\uefdie et la zygosit\ue9 ont \ue9t\ue9 \ue9valu\ue9es \ue0 l\u2019aide de la cytom\ue9trie en flux et de l\u2019analyse du polymorphisme mononucl\ue9otidique, respectivement. Le pollen a germ\ue9 sur le stigmate, s\u2019est d\ue9velopp\ue9 dans le style \ue0 travers le bec nucellaire, mais n\u2019a pas atteint le sac embryonnaire, n\u2019obtenant ainsi aucune f\ue9condation dans toutes les 5756 fleurs autogames. Il y avait une r\ue9duction de la germination du pollen (in vitro et in vivo), de la p\ue9n\ue9tration du tube pollinique et de la nouaison avec l\u2019augmentation de la temp\ue9rature. Le pollen trait\ue9 thermiquement a stimul\ue9 la division de l\u2019ovule et induit le d\ue9veloppement de fruits parth\ue9nocarpiques. Les 6 embryo\uefdes par ovule ont \ue9t\ue9 observ\ue9s et toutes les plantules r\ue9g\ue9n\ue9r\ue9es \ue9taient diplo\uefdes, avec 93,0% d\u2018augmentation d\u2019homozygotie. Pour la premi\ue8re fois, la r\ue9g\ue9n\ue9ration des plantes \ue0 partir des ovules, pollinis\ue9es avec du pollen frais 14 jours apr\ue8s la pollinisation, a \ue9t\ue9 r\ue9alis\ue9e, indiquant une vitesse am\ue9lior\ue9e de r\ue9g\ue9n\ue9ration des plantes. Les donn\ue9es g\ue9n\ue9r\ue9es sont importantes pour l\u2019\ue9laboration de protocoles de production de plantes de manioc de DH

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

Fruit set and plant regeneration in cassava following interspecific pollination with castor bean

The increasing demand for cassava ( Manihot esculenta Crantz) for food and non-food uses in the tropics necessitates that its breeding for increased root productivity be made faster. The characteristic long breeding cycle and heterozygous nature of this crop, pose a major obstacle to its rapid genetic improvement. This study aimed at inter-pollinating cassava with castor bean ( Ricinus communis ), with a purpose of inducing and regenerating cassava doubled haploids (DHs). A total of 3,349 flowers from twelve elite cassava varieties were inter-pollinated with caster bean. A total of 803 fruits were harvested for early embryo rescue and/or ovule culture. Of these, three were dissected to obtain seven unique embryos, while 800 were dissected to obtain 1312 young ovules, all of which were cultured in vitro. Overall, 82 (6.25%) of the cultured ovules formed callus that originated from the embryosac region, which is haploid. Four out of seven rescued embryos (57.1%) regenerated into plantlets. Ploidy analyses of 24 samples using flow cytometry revealed that 23 of the analysed samples were diploid. However, one callus sample was anueploid. Only one sample had an exceptionally high level of homozygosity ( 84.2%). These findings lay a foundation for future research aimed at induction of haploids in cassava.La demande croissante de manioc (\ua0 Manihot esculenta \ua0Crantz\ua0) \ue0 usage alimentaire et non alimentaire dans les tropiques\ua0n\ue9cessite que sa reproduction pour une productivit\ue9 accrue des racines soit faite plus rapidement.\ua0Le long cycle de reproduction et le caract\ue8re h\ue9t\ue9rozygote de cette plante constituent un obstacle majeur dans la rapidit\ue9 de son am\ue9lioration g\ue9n\ue9tique.\ua0Cette \ue9tude visait \ue0 inter-polliniser le manioc avec le haricot (\ua0 Ricinus communis \ua0), dans le but d\u2019induire et de r\ue9g\ue9n\ue9rer le manioc d\u2019haplo\uefdes doubl\ue9 (HD).\ua0Un total de 3 349 fleurs de douze \ue9lites vari\ue9t\ue9s de manioc ont \ue9t\ue9 inter-pollinis\ue9es avec le haricot.\ua0Un total de 803 fruits ont \ue9t\ue9 r\ue9colt\ue9s pour les embryons pr\ue9matur\ue9s qui etaient sauves et\ua0/ ou la\ua0culture d\u2019ovules\ua0.\ua0Parmi ceux-ci,\ua0trois ont \ue9t\ue9 diss\ue9qu\ue9s pour obtenir sept embryons uniques\ua0,\ua0tandis que 800 ont \ue9t\ue9 diss\ue9qu\ue9s pour obtenir 1312 jeunes ovules, qui ont tous \ue9t\ue9 cultiv\ue9s\ua0in vitro\ua0.\ua0Un total de 82 (6,25%) des ovules en culture ont form\ue9 des cals provenant de la\ua0r\ue9gion\ua0embryonnaire\ua0, qui est haplo\uefde. Quatre parmi sept embryons sauv\ue9s (57,1%) se sont r\ue9g\ue9n\ue9r\ue9s en plantules.\ua0Les analyses de plo\uefdie de 24 \ue9chantillons par cytom\ue9trie en flux ont r\ue9v\ue9l\ue9 que 23 des \ue9chantillons analys\ue9s \ue9taient diplo\uefdes.Cependant, un \ue9chantillon de cals \ue9tait anueplo\uefde.\ua0Un seul \ue9chantillon pr\ue9sentait un niveau d\u2019homozygotie exceptionnellement \ue9lev\ue9\ua0(84,2\ua0%).\ua0Ces r\ue9sultats sont les bases des recherches dans le futur sur la cause des haplo\uefdes dans le manioc

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