Management of African root and tuber scale using improved cassava genotypes and mineral fertilisers

The African root and tuber scale (ARTS), Stictococcus vayssierei Richard, is an insect species indigenous to Africa, which has recently become an economic pest of cassava (Manihot esculenta Crantz) in many parts of the Democratic Republic of the Congo (D R C). This scale infests underground parts of the plants and prevents young plants from tuberising, thus, causing yield losses of up to 100%. In order to evaluate control components that can be combined into an effective strategy for the management of the scale, six improved cassava genotypes were evaluated for resistance against the scale and NPK fertiliser was tested at the recommended rate as a pest control component. The fertiliser application was made as basal dressing and on one improved clone (F100) with a local variety. Results indicated that ARTS infestations were delayed on ‘Kinuani', F100 and the local clone, ‘Kileba', as no scales were observed on them 6 months after planting (MAP). The sweetest improved genotype, ‘Papayi', harboured the highest number (134.8 insects plant-1) of scales. At 9 and 12 (harvest) MAP, all clones were relatively highly infested, except for the bitter genotype, ‘Sadisa'. This clone also yielded more than the local clone. Mineral fertiliser application significantly increased scale population density on F100, and plant height on both F100 and the local clone. It did not significantly affect the number of tuberous roots and root yield on either the improved F100 or on ‘Kileba'. Key Words: Democratic Republic of Congo, Manihot, Stictococcus vayssierei RÉSUMÉ La gamme des racines et tubercules Africains, Stictococus vayssierei Richard, est une espèce indigène à l'Afrique qui est récemment devenue une peste économique de manioc (Manihot esculenta Crantz) dans beaucoup d'endroits de la République Démocratique du Congo (RDC). Cette gamme infecte les parties souterraines des plantes et empêche les jeunes plantes à former les tubercules, causant ainsi des pertes de rendements jusqu\'à 100%. En vue d'évaluer les composants de contrôle qui peuvent être combinés dans une stratégie effective pour la gestion de la gamme, six génotypes améliorés de manioc étaient évalués pour la résistance contre la gamme et le fertilisant NPK était testé au taux recommandé comme un composant de désinsectisation. L'application de fertilisant était faite comme engrais fondamental et sur un clone amélioré (F100) avec une variété locale. Les résultats ont indiqué que les infestations de la gamme des racines et tubercules Africains étaient retardées sur ‘ Kinuani', F100 et le clone local, ‘kileba', étant donné qu'aucune gamme n'était observée sur eux 6 mois après plantations (MAP). Le génotype amélioré le plus sucré, ‘Papayi', a hébergé le nombre le plus élevé (134,8 insectes plante-1) de gamme. A 9 et 12 mois (récolte) MAP, tous les clones étaient relativement gravement infectés, à l'exception du génotype amère, ‘Sadisa'. Ce clone a aussi produit plus que le clone local. L'application de fertilisant minéral a significativement augmenté la densité de population de gamme sur F100 et sur le clone local. Il n'a pas significativement affecté le nombre des racines tubercules et la racine produite sur le F100 amélioré ou sur ‘Kilemba'. Mots clés: République Démocratique du Congo, Manihot, Stictococus vayssierei African Crop Science Journal Vol.12(3) 2004: 217-22

Management of African root and tuber scale using improved cassava genotypes and mineral fertilizers

The African root and tuber scale (ARTS), Stictococcus vayssierei Richard, is an insect species indigenous to Africa, which has recently become an economic pest of cassava (Manihot esculenta Crantz) in many parts of the Democratic Republic of the Congo (D R C). This scale infests underground parts of the plants and prevents young plants from tuberising, thus, causing yield losses of up to 100%. In order to evaluate control components that can be combined into an effective strategy for the management of the scale, six improved cassava genotypes were evaluated for resistance against the scale and NPK fertiliser was tested at the recommended rate as a pest control component. The fertiliser application was made as basal dressing and on one improved clone (F100) with a local variety. Results indicated that ARTS infestations were delayed on ‘Kinuani', F100 and the local clone, ‘Kileba', as no scales were observed on them 6 months after planting (MAP). The sweetest improved genotype, ‘Papayi', harboured the highest number (134.8 insects plant-1) of scales. At 9 and 12 (harvest) MAP, all clones were relatively highly infested, except for the bitter genotype, ‘Sadisa'. This clone also yielded more than the local clone. Mineral fertiliser application significantly increased scale population density on F100, and plant height on both F100 and the local clone. It did not significantly affect the number of tuberous roots and root yield on either the improved F100 or on ‘Kileba'

The impact of the emergency response to the outbreak of the cassava mosaic disease in the Democratic Republic of Congo

This paper evaluates the impact of an emergency research for development project implemented in the Democratic Republic of Congo from 2000 to 2009 by a various actors including the International Institute of Tropical Agriculture in response to the outbreak of the Cassava Mosaic Disease that threatened the national food security. It applies methods developed in the econometric and statistical treatment effects literature on evaluation of social programs. The study evaluates impact by analyzing changes over time of outcomes of sample households in the project areas compared to neighboring non-project areas. We find that the project had statistically significant positive effects on technology adoption, area planted cassava, productivity, profitability,household food security and aggregate supply response. The effects are strongest among lower tails of distribution of outcomes mostly made up of female-headed households who grew the crop mainly for food. These findings are useful for informing agricultural and food policy debates in Africa

Does a cassava researchfordevelopment program have impact at the farm level? Evidence from the Democratic Republic of Congo

This paper evaluates the impact of a cassava research-for-development program on farm level outcomes.The program was implemented in the Democratic Republic of Congo from 2001 to 2009. We apply pro-pensity score matching, Rosenbaum bounds on treatment effects, Altonji et al. method of selection onobservables and unobservables and endogenous switching regression to farm survey data collected dur-ing the 2009 cropping season. We use these methods to test whether the R4D program has a statisticallysignificant effect on outcomes of interest and if these are not driven by selection on unobservables. Usingpropensity score matching, we find statistically significant positive effects on household participation incassava markets, adoption of improved varieties and crop management practices and household foodadequacy; and no statistically significant effects on yields and profits. The results show that bias dueto selection on unobservables is not severe enough to invalidate the impact estimates. Bias may stillbe a problem that is present in the analysis. But there is evidence that it is not substantial. Althoughthe program does not have a statistically significant positive effect on yields and profits, the significantprogram effects on market participation, variety adoption, and food adequacy merit further promotionof the program since these positive outcomes tend to be pre-conditions for realizing long-term yieldand profit benefits

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

Genetic diversity of cassava (Manihot esculenta Crantz) landraces and cultivars from southern, eastern and central Africa

Studies to quantify genetic variation in cassava germplasm, available within the national breeding programmes in Africa, have been limited. Here, we report on the nature and extent of genetic variation that exists within 1401 cassava varieties from seven countries: Tanzania (270 genotypes); Uganda (268); Kenya (234); Rwanda (184); Democratic Republic of Congo (DRC; 177); Madagascar (186); Mozambique (82). The vast majority of these genotypes do not exist within a formal germplasm conservation initiative and were derived from farmers' fields and National Agricultural Research Systems breeding programmes. Genotypes were assayed using 26 simple sequence repeat markers. Moderate genetic variation was observed with evidence of a genetic bottleneck in the region. Some differentiation was observed among countries in both cultivars and landraces. Euclidean distance revealed the pivotal position of Tanzanian landraces in the region, and STRUCTURE analysis revealed subtle and fairly complex relationships among cultivars and among landraces and cultivars analysed together. This is likely to reflect original germplasm introductions, gene flow including farmer exchanges, disease pandemics, past breeding programmes and the introduction of cultivars from the International Institute of Tropical Agriculture – Nigeria. Information generated from this study will be useful to justify and guide a regional cassava genetic resource conservation strategy, to identify gaps in cassava diversity in the region and to guide breeding strategies