Limits of phytosanitation and host plant resistance towards the control of cassava viruses in Uganda

Published online: 30 Sept 2017Cassava (Manihot esculenta Crantz) and the viruses that infect it, notably cassava mosaic virus and cassava brown streak viruses, have a unique history of co-evolution and co-existence. While cassava originated in South America, both viruses and the diseases they cause have largely been limited to the East African region, where they have, and continue to be key yield-robbing stresses. For sustainable control, we assume that deployment of resistant varieties when carefully combined with phytosanitation will combat these viruses. We have thus generated empirical data and tested the limits, i.e., how long this strategy can last. This entailed the comparison of elite cassava varieties, one set of virus-indexed tissue culture plantlets, and the other set, re-cycled planting materials under farmer’s cyclic propagation for 6-23 years. Trials were established at diverse sites in Uganda. We observed that both officially-released and unofficially-released cassava varieties are common in farmer’s fields; these varieties have varying susceptibility levels to viruses. Worrisome was that some officially-released varieties like NASE 3 registered cassava mosaic disease (CMD) incidences of up to 71% (virus-indexed), which was not any different from its re-cycled counterparts. Other varieties like NASE 14 have maintained high levels of CMD resistance six years after official release. Predominant re-cycled cassava varieties notably TME 204, I92/0057, TME 14, and to a limited extent NASE 14, are key reservoirs for cassava brown streak disease (CBSD) associated viruses. These findings highlight the limits of phytosanitation, i.e., in areas like Kaberamaido associated with high CMD pressure, varieties NASE 1 and NASE 3 can not be recommended; on the contrary, these varieties can be deployed in Kalangala, where they can survive with phytosanitation. And for CBSD, the findings justify the urgent need for phytosanitation (community-led) and development of varieties with higher levels of resistance and/or tolerance, as no immune variety has so far been identified

Improvement of local cassava germ plasm in Uganda

No Abstrac

Variation in qualitative and quantitative traits of cassava germplasm from selected national breeding programmes in subSaharan Africa

An improved understanding of phenotypic variation within cassava germplasm in southern, eastern and central Africa will help to formulate knowledge-based breeding strategies. Thus, the overall objective of this study was to examine the phenotypic variation in cassava germplasm available within six breeding programmes in Africa, namely Uganda, Kenya, Tanzania, Rwanda, Democratic Republic of Congo and Madagascar. In each country, single-row plots were used for assessment of 29 qualitative traits and evaluation of four quantitative traits: root dry matter content (DMC), harvest index (HI), leaf retention (LR) and root cortex thickness. Qualitative traits provided limited discrimination of cassava germplasm. However, differences in DMC, HI, LR and root cortex thickness were observed among the germplasm indicating scope for genetic improvement. Highest average DMC was registered in Uganda (39.3%) and lowest in Tanzania (30.1%), with the elite genotypes having a relatively higher DMC than local genotypes. Highest average HI was observed in Uganda (0.60) and lowest in Kenya (0.32). Cassava genotypes displayed varied root peel thickness (0.34–4.89 mm). This study highlights variation in agronomic traits that could be exploited to increase cassava productivity

A breeding scheme for local adoption of cassava (Manihot esculenta Crantz)

In many rural communities, cassava mosaic disease (CMD) resistant varieties are being rejected by farmers owing to their inferior root qualities when compared to locally adapted varieties. In response to this challenge, we implemented a breeding scheme whose objective was to combine CMD resistance with farmer preferred root qualities, whose genes were respectively sourced for elite and local varieties. We targeted to achieve this goal within five years that comprised of: i) hybridization of complementary parental lines, ii) seedling evaluation trial (SET); iii) clonal evaluation trial (CET); iv) modified preliminary yield trial (MPYT) and v) modified uniform yield trial (MUYT). At SET and CET, emphasis was placed on traits of moderate to high heritability while for MPYT and MUYT emphasis was on traits of low heritability. Generated F 1 progeny (4080 half sibs) were established in SET of which 1014 seedlings were selected and advanced to the CET. At CET, only 143 clones were selected and advanced. Under MPYT, slightly less than 50% of the clones were selected, while under MUYT, (8 to 40 clones per site) were selected. Clones selected per site were characterized by: DMC (28 to 38%); ii) HI (0.26 to 0.62); iii) yield (14 to 59 t/ha), resistance to CMD and desirable farmer root qualities. Given this outcome, we have demonstrated the utility of this scheme in accelerating development of locally adapted cassava varieties and thus propose the scheme be referred to as "speed cassava breeding"

Care of Ebola Survivors and Factors Associated With Clinical Sequelae—Monrovia, Liberia

BackgroundThe Eternal Love Winning Africa (ELWA) Clinic was the first clinic to provide free, comprehensive care to Ebola virus disease (EVD) survivors in Liberia. The objectives of this analysis were to describe the demographics and symptoms of EVD survivors at ELWA from January 2015 through March 2017 and to identify risk factors for development of sequelae.MethodsPatients' demographic and clinical information was collected by chart review in June 2016 and March 2017. Associations with clinical sequelae were analyzed using the chi-square test, t test, and multivariate logistic regression.ResultsFrom January 2015 to March 2017, 329 EVD survivors were evaluated at ELWA. Most survivors experienced myalgia/arthralgia (73%; n = 239) and headache (53%; n = 173). The length of time from Ebola Treatment Unit (ETU) discharge to first clinic visit ranged from 0 to 30 months. Many visits (30%) occurred 24 or more months after ETU discharge. The proportion of visits for headache, weight loss, joint pain, visual problems, insomnia, fatigue, memory loss, decreased libido, depression, and uveitis decreased over time. More men than women had visits for depression; however, these differences were not significant. Symptom prevalence differed in adults and children; significantly more adults experienced myalgia/arthralgia (77% vs 44%), visual problems (41% vs 12%), post-EVD-related musculoskeletal pain (42% vs 15%), and insomnia (17% vs 2%).ConclusionsEVD survivors frequented ELWA for EVD-related symptoms many months after ETU discharge, indicating a long-term need for care. Reported symptoms changed over time, which may reflect eventual resolution of some sequelae