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

Production of friable embryogenic callus and regeneration of Ugandan farmer-preferred cassava genotypes

Generation of embryogenic callus is a key step in genetic engineering of many crop species, including cassava. Protocols for generation of friable embryogenic callus (FEC) have been lacking for Ugandan cassava genotypes, thereby delaying their genetic engineering for agronomic and other desirable traits. The objective of this study was to determine conditions suitable for production and regeneration of FEC in the Ugandan cassava genotypes; Aladu, Bukalasa and Ebwanateraka, and control cultivar 60444. Immature leaf lobe explants were established on Murashige and Skoog (MS) based media for initiation of organized embryogenic callus (OES). To produce FEC, resulting OES were established on Gresshoff and Doy based callus induction media with varying levels of sucrose, maltose, tyrosine, tryptophan, naphthalene acetic acid (NAA) under light and dark conditions. Subsequently, FEC was subcultured to MS-based embryo maturation and embryo regeneration media. All genotypes produced OES. All genotypes produced FEC except Bukalasa. The amino acid tyrosine favoured production of FEC in Aladu and Ebwanatereka, but not in 60444, while 20 g/L of sucrose trigged production of FEC in Aladu and 60444, but 40 g/L of sucrose was superior for Ebwanatereka. Media supplemented with 1 ml/L naphthalene acetic acid NAA facilitated embryo regeneration in Ebwanatereka and 60444, while Aladu responded better to 5 ml/L NAA. Light, tyrosine and sucrose were essential for FEC production in Uganda cultivars while NAA was required for regeneration of somatic embryos. Ability to produce FEC in these genotypes lays a foundation for their improvement through genetic transformation for the desired and agronomic traits.Key words: Cassava (Manihot esculenta Crantz), somatic embryogenesis, amino acids, carbon sources

Morphotypes, distribution and uses of false banana in Uganda

Enset ( Ensete ventricosum ) is commonly known as the \u201cfalse banana\u201d because of its close resemblance to the domesticated banana ( Musa spp.) plant. It is Ethiopia\u2019s most important traditional staple crop in the densely populated south and south-western parts of the country; where it is grown and exploited for its starch to make various food and industrial products. In Uganda, little is known about enset regarding its ethno-botany and distribution, yet it occurs in the country. The objective of this study was to map out the distribution and document the ethno-botany and uses of enset in Uganda. A survey was carried out throughout the country to identify its natural habitats in different regions. Local people were interviewed on the uses of enset, etymology, and identification of different morphotypes. Morphological descriptors and sex of enset accessions were used in classification or identification of morphotypes. Enset was generally widely, but sparsely distributed in the different regions in Uganda; growing at elevations ranging between 988 (Moyo district) to 2,150 (Kapchorwa district) metres above sea level (masl) and in a variety of habitats. Out of the 80 districts of Uganda (as of 2009), enset was reported and observed in 30 districts. Thirteen local names of enset and their meanings were documented; but it was widely referred to as Kitembe. Different plant parts were used for medicinal purposes; while the leaves were used in local beer brewing. There were five enset morphotypes distinguished by morphological traits, such as plant height (short vs tall), mid-rib colour (light green vs pink), pseudostem background appearance (light green vs brown), leaf margin colour, male bud colour, and leaf length-breadth ratio. A detailed molecular level genetic diversity assessment is recommended for further validation of the morphotypes.Le Bananier d\u2019Abyssinie ( Ensete ventricosum ) est commun\ue9ment appel\ue9 comme \uab\ua0fausse banane\ua0\ubb \ue0 cause de sa tr\ue8s grande ressemblance au plant de banane ( Musa spp) domestiqu\ue9. C\u2019est un aliment de base traditionnel tr\ue8s important dans les r\ue9gions de grande densit\ue9 de population du Sud et Sud-Ouest d\u2019Ethiopie\ua0; o\uf9 il est cultiv\ue9 et exploit\ue9 pour son amidon utilis\ue9 pour divers produits alimentaires et industriels. En Ouganda, tr\ue8s peu d\u2019informations relatives \ue0 son ethnobotanique et \ue0 sa distribution sont disponibles sur Bananier d\u2019Abyssinie, pourtant il est pr\ue9sent dans le pays. L\u2019objective de cette \ue9tude \ue9tait de cartographier la distribution et de documenter l\u2019ethnobotanique et les usages du bananier d\u2019Abyssinie en Ouganda. Une enqu\ueate a \ue9t\ue9 conduite \ue0 travers le pays pour identifier ses habitats naturels dans diff\ue9rentes r\ue9gions. Les populations locales ont \ue9t\ue9 interview\ue9es sur les usages du bananier d\u2019Abyssinie, l\u2019\ue9tymologie, et l\u2019identification des diff\ue9rents morphotypes. Les descripteurs morphologiques et le sexe des accessions du bananier d\u2019Abyssinie ont \ue9t\ue9 utilis\ue9s dans la classification ou l\u2019identification des morphotypes. Le bananier d\u2019Abyssinie a \ue9t\ue9 largement, but sporadiquement distribu\ue9 dans les diff\ue9rentes r\ue9gions en Ouganda\ua0; les altitudes de cultures varient entre 988 (district de Moyo) \ue0 2150 m\ue8tres (district de Kapchorwa) au-dessus du niveau de la mer (masl) et dans une vari\ue9t\ue9 d\u2019habitats. Sur les 80 districts (comme en 2009), le bananier d\u2019Abyssinie a \ue9t\ue9 rapport\ue9 et observ\ue9 dans 30 districts. Les treize noms locaux du bananier d\u2019Abyssinie et leurs significations ont \ue9t\ue9 document\ue9s\ua0; mais il a \ue9t\ue9 largement r\ue9f\ue9r\ue9 au Kitembe. Les diff\ue9rentes parties du plant ont \ue9t\ue9 utilis\ue9es \ue0 des fins m\ue9dicinales, alors que les feuilles ont \ue9t\ue9 utilis\ue9es dans la pr\ue9paration de la bi\ue8re locale. Il y avait cinq morphotypes du bananier d\u2019Abyssinie distingu\ue9s par des traits morphologiques, tels que la hauteur du plant (courte vs haute), couleur de mid-nervure (vert-clair vs rose), fond d\u2019apparence de pseudo tige (vert-clair vs marron), couleur de la marge de la feuille, m\ue2le mais la couleur, et un ratio longueur/largeur de la feuille. Une \ue9valuation d\ue9taill\ue9e de la diversit\ue9 g\ue9n\ue9tique mol\ue9culaire est recommand\ue9e pour davantage validation des morphotypes

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

Diurnal oscillation of SBE expression in sorghum endosperm

Spatial and temporal expression patterns of the sorghum SBEI, SBEIIA and SBEIIB genes, encoding, respectively, starch branching enzyme (SBE) I, IIA and IIB, in the developing endosperm of sorghum (Sorghum bicolor) were studied. Full-length genomic and cDNA clones for sorghum was cloned and the SBEIIA cDNA was used together with gene-specific probes for sorghum SBEIIB and SBEI. In contrast to sorghum SBEIIB, which was expressed primarily in endosperm and embryo, SBEIIA was expressed also in vegetative tissues. All three genes shared a similar temporal expression profile during endosperm development, with a maximum activity at 15-24 days after pollination. This is different from barley and maize where SBEI gene activity showed a significantly later onset compared to that of SBEIIA and SBEIIB. Expression of the three SBE genes in the sorghum endosperm exhibited a diurnal rhythm during a 24-h cycle

In vitro embryo rescue and plant regeneration following self-pollination with irradiated pollen in cassava (Manihot esculenta Crantz)

Cassava is a highly heterozygous species; hence, current methods used in classical cassava breedingcannot match the urgent need to high yielding varieties. Recently, progress was made through androgenesis and gynogenesis as pathways for raising doubled cassava haploid lines to overcome problems associated with cassava’s inherent reproductive biology, but these efforts were limited (nocandidate cassava plantlets were regenerated). For the first time, this study shows that pollen irradiation coupled with self-pollination and embryo rescue regenerated 62 candidate cassava plantlets. Plants of an elite cassava variety, Nase14, served as a mother plant and as the pollen donor for the irradiation. Irradiation dosages of 50 to 250 Gray studied across five pollination events and 300 or 500 Gray in one pollination event caused a reduction in pollen germination up to 67.0%. By 15 days after pollination (DAP) with irradiated pollen, up to 89.7% of the pollinated flowers had aborted. By embryo rescue time (42 DAP), significant differences were observed in number of fruits, seeds and embryos generated, with the non-irradiated pollen treatments having significantly higher numbers. Sixteen (16) heterozygous SSR markers in the parent and ploidy analysis showed that none of the regenerated plants was haploid or homozygous. However, the plantlets resulting from pollination with non-irradiated pollen had 56.2% homozygous loci, while progeny derived from irradiated treatments had frequencies of homozygous loci between 28.1 and 55.0%. This is the first time to use irradiated pollen in cassava as a pathway to generate candidate plantlets as an initial step in double haploid production.Key words: Cassava, doubled haploids, embryo rescue, plant regeneration, pollen germination, pollenirradiation

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

Prior infection with SARS-CoV-2 boosts and broadens Ad26.COV2.S immunogenicity in a variant-dependent manner

The Johnson and Johnson Ad26.COV2.S single-dose vaccine represents an attractive option for coronavirus disease 2019 (COVID-19) vaccination in countries with limited resources. We examined the effect of prior infection with different SARS-CoV-2 variants on Ad26.COV2.S immunogenicity. We compared participants who were SARS-CoV-2 naive with those either infected with the ancestral D614G virus or infected in the second wave when Beta predominated. Prior infection significantly boosts spike-binding antibodies, antibody-dependent cellular cytotoxicity, and neutralizing antibodies against D614G, Beta, and Delta; however, neutralization cross-reactivity varied by wave. Robust CD4 and CD8 T cell responses are induced after vaccination, regardless of prior infection. T cell recognition of variants is largely preserved, apart from some reduction in CD8 recognition of Delta. Thus, Ad26.COV2.S vaccination after infection could result in enhanced protection against COVID-19. The impact of the infecting variant on neutralization breadth after vaccination has implications for the design of second-generation vaccines based on variants of concern