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

Root and shoot development during the plant crop and the first ratoon of banana and plantain (Musa spp.) with implications for perennial cultivation on degraded Ultisols in southeastern Nigeria

The effect of cycle on root system and shoot development was studied for two crop cycles (plant crop and first ratoon). The study revealed that shoot and root system development declined from the plant crop to the first ratoon for plants grown on degraded Ultisols in south-eastern Nigeria.El efecto cíclico en el sistema radical y en el desarrollo de otras partes de la planta fue estudiado durante dos ciclos de producción (siembra y primer renuevo). El estudio reveló que el desarrollo del sistema radical y otras partes de la planta declinó desde el momento de la siembra hasta el primer renuevo en plantas sembradas en Ultisoles degradados en el sureste de Nigeria

Relative Performance of Root and Shoot Development in Enset and East African Highland Bananas

East African highland bananas and enset belong to the genera Musa and Ensete ( Ensete ventricosum ), respectively. The root, corm and shoot growth of field-established enset and East African highland banana cultivars was assessed. Banana and wild enset plants were assessed in Uganda, while domesticated enset plants were assessed in Ethiopia. Growth traits of the enset and banana mats in Uganda were recorded at flower emergence of the banana plant crop, while enset plants in Ethiopia were assessed at 4 and 5 years after planting. The results obtained in Uganda indicate that enset had a significantly (P<0.05) shorter and thicker pseudostem compared to banana. In addition, enset had a larger root system with thicker cord roots. Results further showed that young enset plants had a significantly lower shoot-root ratio compared to the bananas. The shoot-root ratio in enset is, however, clone dependent and increases with an increase in age. The results also showed that root density in enset sharply decreases with increasing soil depth.Les bananas de montagne d&apos;Afrique de l&apos;Est appartiennent respectivement à l&apos;espèce genera Musa , et Ensete ( Ensete ventricosum ), La croissance des racines, bulbes et rejetons de champ-établi d&apos;enset et de cultivars de banane de montagne d&apos;Afrique de l&apos;Est, ont été évaluée. La banane et les plantes d&apos;enset sauvages ont été évaluées en Ouganda, pendant que les plantes d&apos;enset domestiqué ont été évaluées en Ethiopie. Les traits de croissance des tapis d&apos;enset et banane en Ouganda ont été enregistrés à l&apos;apparition de fleur de la récolte de plante de banane, pendant que les plantes d&apos;enset en Ethiopie ont été évaluées à 4 et 5 ans après la plantation Les résultats obtenus en Ouganda indiquent que cet enset a eu significativement (P<0.05) pseudostem plus court et plus épais à comparer à la banane. Par ailleurs, enset a un plus grand système fondamental avec les racines de corde plus épaisses. Les résultats poussés ont montré que ces jeunes plantes d&apos;enset ont une grande proportion des rejetons en comparaison avec celle des bananes. La proportion des rejetons de enset est cependant un clone dépendant des augmentations de l&apos;âge. Les résultats ont montré aussi que la densité des racines de enset diminue avec l&apos;augmentation de la profondeur du sol

The effectiveness of different herbicides in the destruction of banana Xanthomonas wilt infected plants

Early detection followed by the destruction of infected mats is one of the recommended and effective methods of controlling banana Xanthomonas wilt. As manual destruction is very tedious and time consuming, herbicide injections in the pseudostem or the stump were evaluated as a suitable alternative. The study was carried out in Luwero district in central Uganda. Herbicide injections were made on &apos;Pisang Awak&apos; plants ( Musa ABB group) using different concentrations of Roundup and 2,4-D at a pseudostem height of 30 and 100 cm. In addition, the herbicide was injected in the centre (diameter-wise) and in the peripheral part of the pseudostem (tangential-wise). Herbicide applications into the stump were also evaluated. All plants (100%) injected with 2,4-D had fallen and started rotting by three weeks after application. However, at three weeks, none of the plants treated with Roundup, regardless of the concentration and the height of injection had died. Similarly plants injected with 2,4-D had less re-sprouting compared to plants treated with Roundup. Therefore, 2,4-D is more effective than Roundup in destroying &apos;Pisang Awak&apos; plants and in suppressing the re-sprouting of lateral shoots. Since 2,4-D is also cheaper than Roundup it is recommended for use on small-scale plantations. At least 1.6 ml of the original concentrate of 2,4-D and 2.0 ml of the original concentrate of Roundup needs to be applied per mature plant. The most effective pseudostem injection height was found to be 100 cm. The angle of injection whether peripherally or central and the plant growth stage did not affect the herbicides&apos; efficiency. The results also showed that pseudostem injections are more effective than stump herbicide applications.Tôt la détection suivie par la destruction de tapis infectés est une des méthodes recommandées de contrôle efficaces de flanchent de Xanthomonas de banane. Comme la destruction manuelle est très ennuyeuse et le temps consommation des injections d&apos;herbicide dans le pseudostem ou la souche ont été évaluées comme une alternative convenable. L&apos;étude a été exécutée dans le quartier de Luwero en Ouganda central. Les injections d&apos;herbicide ont été faites sur les plantes (le groupe d&apos;ABB de Musa ) utilisant des concentrations différentes de Rassemblement et 2,4-D à une hauteur de pseudostem de 30 et 100 cm. Par ailleurs, l&apos;herbicide a été injecté au centre (diamètre-sage) et dans la partie périphérique du pseudostem (tangentiel-sage). Les applications d&apos;herbicide dans la souche ont été aussi évaluées. Toutes les plantes (100%) injecté avec 2,4-D était tombé et avait commencé à pourrir après trois semaines d&apos;application. Cependant, à trois semaines, aucun des plantes traitées avec le Rassemblement, sans tenir compte de la concentration et la hauteur d&apos;injection n&apos;était mort. De même les plantes injectées avec 2,4-D ont au moins re-poussées en comparaison avec des plantes traitées avec le Rassemblement. Donc, 2,4-D est plus efficace que le Rassemblement des plantes et en éliminant le re-pousses latéral des rejetons. Puisque 2,4-D est aussi plus bon marché que le Rassemblement qu&apos;il est recommandé pour l&apos;usage sur les plantations à petite échelle. Au moins 1,6 ml du concentré original de 2,4-D et 2,0 ml du concentré original de besoins de Rassemblement être appliqué par la plante mûre. La plus efficace injection pseudostem été trouvée pour être 100 cm. L&apos;angle d&apos;injection si périphérique ou central et l&apos;étape de croissance de la plante n&apos;ont pas affecté l&apos;efficacité des herbicides >. Les résultats ont montré aussi que les injections de pseudostem sont plus efficaces que d&apos;applications d&apos;herbicide à la souche

Relationship between root and shoot growth traits during the plant crop and first ratoon in banana and plantain (Musa spp.) and its implications for perennial cultivation on degraded Ultisols in southeastern Nigeria.

The effect of cycle on root system and shoot development was studied for two crop cycles (plant crop and first ratoon). The study revealed that shoot and root system development declined from the plant crop to the first ratoon for plants grown on degraded Ultisols in south-eastern Nigeria

Physiological and molecular characterization of drought responses and identification of candidate tolerance genes in cassava

Cassava is an important root crop to resource-poor farmers in marginal areas, where its production faces drought stress constraints. Given the difficulties associated with cassava breeding, a molecular understanding of drought tolerance in cassava will help in the identification of markers for use in marker-assisted selection and genes for transgenic improvement of drought tolerance. This study was carried out to identify candidate drought-tolerance genes and expression-based markers of drought stress in cassava. One drought-tolerant (improved variety) and one drought-susceptible (farmer-preferred) cassava landrace were grown in the glasshouse under well-watered and water-stressed conditions. Their morphological, physiological and molecular responses to drought were characterized. Morphological and physiological measurements indicate that the tolerance of the improved variety is based on drought avoidance, through reduction of water loss via partial stomatal closure. Ten genes that have previously been biologically validated as conferring or being associated with drought tolerance in other plant species were confirmed as being drought responsive in cassava. Four genes (MeALDH, MeZFP, MeMSD and MeRD28) were identified as candidate cassava drought-tolerance genes, as they were exclusively up-regulated in the drought-tolerant genotype to comparable levels known to confer drought tolerance in other species. Based on these genes, we hypothesize that the basis of the tolerance at the cellular level is probably through mitigation of the oxidative burst and osmotic adjustment. This study provides an initial characterization of the molecular response of cassava to drought stress resembling field conditions. The drought-responsive genes can now be used as expression-based markers of drought stress tolerance in cassava, and the candidate tolerance genes tested in the context of breeding (as possible quantitative trait loci) and engineering drought tolerance in transgenics

Lecture III

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 compréhension de la diversité génétique est une condition importante dans la sélection de diverses combinaisons parentales et la formation des groupes héterotiques d’intérêt génétique pour l’amélioration des cultures. Cette étude était conduite pour déterminer la diversité génétique parmi 51 variétés locales de manioc ( Manihot esculenta ) préférées des fermiers et 15 accessions élites cultivées en Ouganda. Vingt six marqueurs simples à sequence répétée (SSR) utilisés pour l’évaluation de la diversité génétique ont révélé un total de 154 allèles, parmi lesquelles 24% étaient des allèles uniques présentes dans les races locales seulement. La diversité génétique et l’héterozygosité observées dans les races locales étaient légèrement supérieures que dans les accessions élites. Celles-ci s’étaient regroupées avec quelques variétés locales indiquant donc qu’elles avaient quelques allèles en commun. Par ailleurs, 58.8% des races locales ont formé trois différents groupes indépendamment des accessions élites. Inclure ces races locales à allèles uniques dans les systèmes d’amélioration du manioc permettra d’augmenter les chances de produire des cultivars élites préférés des fermiers. L’étude montre aussi que la différenciation génétique trouvée parmi les accessions de différentes régions est une opportunité offerte pour l’établissement des groupes héterotiques dans le programme d’amélioration

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

Banana Xanthomonas wilt: a review of the disease, management strategies and future research directions

Banana production in Eastern Africa is threatened by the presence of a new devastating bacterial disease caused by Xanthomonas vasicola pv. musacearum (formerly Xanthomonas campestris pv. musacearum). The disease has been identified in Uganda, Eastern Democratic Republic of Congo, Rwanda and Tanzania. Disease symptoms include wilting and yellowing of leaves, excretion of a yellowish bacterial ooze, premature ripening of the bunch, rotting of fruit and internal yellow discoloration of the vascular bundles. Plants are infected either by insects through the inflorescence or by soil-borne bacterial inoculum through the lower parts of the plant. Short- and long-distance transmission of the disease mainly occurs via contaminated tools and insects, though other organisms such as birds may also be involved. Although no banana cultivar with resistance to the disease has been identified as yet, it appears that certain cultivars have mechanisms to ‘escape’ the disease. Management and control of the disease involve methods that reduce the inoculum’s density and spread of the pathogen. Removal of the male bud (de-budding) has proven to be very effective in preventing the disease incidence since the male bud appears to be the primary infection site. The economic impact of banana Xanthomonas wilt is not fully understood but its impact on food security in the region is very significant. While germplasm screening for the disease is ongoing, efforts to genetically engineer resistance in some banana cultivars are also making good progress. This paper presents a review of the disease and management strategies that have been successful in curtailing its spread