Ukiriguru Agricultural Research Institute

Mwanza, Tanzania

Ukiriguru Agricultural Research Institute

Mwanza, Tanzania
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Masumba E.A.,Sugarcane Research Institute | Masumba E.A.,University of Pretoria | Kapinga F.,Naliendele Agricultural Research Institute | Mkamilo G.,Naliendele Agricultural Research Institute | And 11 more authors.
Theoretical and Applied Genetics | Year: 2017

Key message: QTL consistent across seasons were detected for resistance to cassava brown streak disease induced root necrosis and foliar symptoms. The CMD2 locus was detected in an East African landrace, and comprised two QTL. Abstract: Cassava production in Africa is compromised by cassava brown streak disease (CBSD) and cassava mosaic disease (CMD). To reduce costs and increase the precision of resistance breeding, a QTL study was conducted to identify molecular markers linked to resistance against these diseases. A bi-parental F1 mapping population was developed from a cross between the Tanzanian farmer varieties, Namikonga and Albert. A one-step genetic linkage map comprising 943 SNP markers and 18 linkage groups spanning 1776.2 cM was generated. Phenotypic data from 240 F1 progeny were obtained from two disease hotspots in Tanzania, over two successive seasons, 2013 and 2014. Two consistent QTLs linked to resistance to CBSD-induced root necrosis were identified in Namikonga on chromosomes II (qCBSDRNFc2Nm) and XI (qCBSDRNc11Nm) and a putative QTL on chromosome XVIII (qCBSDRNc18Nm). qCBSDRNFc2Nm was identified at Naliendele in both seasons. The same QTL was also associated with CBSD foliar resistance. qCBSDRNc11Nm was identified at Chambezi in both seasons, and was characterized by three peaks, spanning a distance of 253 kb. Twenty-seven genes were identified within this region including two LRR proteins and a signal recognition particle. In addition, two highly significant CMD resistance QTL (qCMDc12.1A and qCMDc12.2A) were detected in Albert, on chromosome 12. Both qCMDc12.1A and qCMDc12.2A lay within the range of markers reported earlier, defining the CMD2 locus. This is the first time that two loci have been identified within the CMD2 QTL, and in germplasm of apparent East African origin. Additional QTLs with minor effects on CBSD and CMD resistance were also identified. © 2017 The Author(s)

Rabbi I.Y.,International Institute Of Tropical Agriculture | Kulembeka H.P.,Ukiriguru Agricultural Research Institute | Masumba E.,Sugarcane Research Institute | Marri P.R.,University of Arizona | Ferguson M.,IITA c o ILRI
Theoretical and Applied Genetics | Year: 2012

Cassava (Manihot esculenta Crantz) is one of the most important food security crops in the tropics and increasingly being adopted for agro-industrial processing. Genetic improvement of cassava can be enhanced through marker-assisted breeding. For this, appropriate genomic tools are required to dissect the genetic architecture of economically important traits. Here, a genome-wide SNP-based genetic map of cassava anchored in SSRs is presented. An outbreeder full-sib (F1) family was genotyped on two independent SNP assay platforms: an array of 1,536 SNPs on Illumina's GoldenGate platform was used to genotype a first batch of 60 F1. Of the 1,358 successfully converted SNPs, 600 which were polymorphic in at least one of the parents and was subsequently converted to KBiosciences' KASPar assay platform for genotyping 70 additional F1. High-precision genotyping of 163 informative SSRs using capillary electrophoresis was also carried out. Linkage analysis resulted in a final linkage map of 1,837 centi-Morgans (cM) containing 568 markers (434 SNPs and 134 SSRs) distributed across 19 linkage groups. The average distance between adjacent markers was 3. 4 cM. About 94. 2% of the mapped SNPs and SSRs have also been localized on scaffolds of version 4. 1 assembly of the cassava draft genome sequence. This more saturated genetic linkage map of cassava that combines SSR and SNP markers should find several applications in the improvement of cassava including aligning scaffolds of the cassava genome sequence, genetic analyses of important agro-morphological traits, studying the linkage disequilibrium landscape and comparative genomics. © 2012 Springer-Verlag.

Ndyetabula I.L.,Maruku Agricultural Research Institute | Merumba S.M.,Maruku Agricultural Research Institute | Jeremiah S.C.,Ukiriguru Agricultural Research Institute | Kasele S.,Ukiriguru Agricultural Research Institute | And 3 more authors.
Plant Disease | Year: 2016

Cassava brown streak disease (CBSD), caused by cassava brown streak viruses, is recognized as one of the most important plant disease threats to African food security. This study describes the incidence and severity of the different symptom types caused by CBSD, derived from extensive surveys in the country most severely affected by the disease: Tanzania. Total plant incidence and mean root severity of CBSD, recorded from 341 farmers’ fields, were both greater in the Coast Zone (49.5% and 3.05), than in the Lake Zone (32.7% and 2.57). Overall, the differing incidences recorded declined in the following order: total plant incidence (39.1%), plant shoot incidence (33.4%), plant root incidence (19.3%), root incidence (10.5%), and unusable root incidence (5.4%). The much lower-than-anticipated loss due to the root necrosis that is characteristic of CBSD was offset by large reductions of root number in plants expressing foliar symptoms of CBSD (15.7% in the Coast Zone and 5.5% in the Lake Zone). These data suggest that the effects of CBSD on the growth of affected plants are greater than those due to root spoilage. Based on these two factors, annual losses due to CBSD in the parts of Tanzania surveyed were estimated at >860,000 t, equivalent to more than U.S.$51 million. A novel approach to using farm-derived data on the responses of the most frequently cultivated varieties to CBSD infection allowed the grouping of the varieties into four categories, based on their relative resistance or tolerance to infection. This tool should be of value to breeders in identifying and selecting for sources of resistance or tolerance in both local and exotic germplasm, and should ultimately contribute to enhancing the management of one of Africa’s most damaging crop diseases. © 2016 The American Phytopathological Society.

Hokanson K.E.,University of Minnesota | Ellstrand N.C.,University of California at Riverside | Dixon A.G.O.,International Institute Of Tropical Agriculture | Kulembeka H.P.,Ukiriguru Agricultural Research Institute | And 2 more authors.
Transgenic Research | Year: 2016

The probability and consequences of gene flow to wild relatives is typically considered in the environmental risk assessment of genetically engineered crops. This is a report from a discussion by a group of experts who used a problem formulation approach to consider existing information for risk assessment of gene flow from cassava (Manihot esculenta) genetically engineered for virus resistance to the ‘wild’ (naturalized) relative M. glaziovii in East Africa. Two environmental harms were considered in this case: (1) loss of genetic diversity in the germplasm pool, and (2) loss of valued species, ecosystem resources, or crop yield and quality due to weediness or invasiveness of wild relatives. Based on existing information, it was concluded that gene flow will occur, but it is not likely that this will reduce the genetic diversity in the germplasm pool. There is little existing information about the impact of the virus in natural populations that could be used to inform a prediction about whether virus resistance would lead to an increase in reproduction or survival, hence abundance of M. glaziovii. However, an increase in the abundance of M. glaziovii should be manageable, and would not necessarily lead to the identified environmental harms. © 2015, Springer International Publishing Switzerland.

Kulembeka H.P.,Ukiriguru Agricultural Research Institute | Ferguson M.,International Institute Of Tropical Agriculture | Herselman L.,University of the Free State | Kanju E.,International Institute Of Tropical Agriculture | And 4 more authors.
Euphytica | Year: 2012

Cassava brown streak disease (CBSD) is an economically important virus disease causing significant losses to cassava root yield and quality in east, central and southern Africa. Breeding for resistance in cassava requires an understanding of the underlying genetic control of CBSD resistance. Sources of CBSD resistance are available but little is known on the value of those varieties as parents for CBSD resistance breeding. Two resistant and two susceptible varieties were crossed in a half diallel design and 35 F 1 progeny from each of the six families, plus parents, were screened at two locations in a randomised complete block design with four replications in warm sub-humid environments of coastal Tanzania in 2008. Screening for CBSD field resistance was done using disease severity scoring on a scale of 1-5. Significant variations in disease severity were observed for crosses, general combining ability (GCA) and specific combining ability (SCA) at both locations. The CBSD shoot symptom severity scores ranged from 1 to 4.4 while root necrosis ranged from 1. 3 to 4.5. The contribution of GCA to the total sum of squares of crosses for disease scores ranged from 86.9 to 95.2 % compared to SCA that ranged from 4.8 to 14.2 %. Additive gene effects were more important than non-additive effects indicating that CBSD resistance is genetically determined and that selection should be successful to improve resistance. Selection of parents with good GCA effects will be important for success in CBSD resistance breeding. © 2012 Springer Science+Business Media B.V.

Legg J.P.,International Institute Of Tropical Agriculture | Shirima R.,International Institute Of Tropical Agriculture | Tajebe L.S.,University of Catania | Guastella D.,University of Catania | And 5 more authors.
Pest Management Science | Year: 2014

Cassava mosaic disease and cassava brown streak disease are caused by viruses transmitted by Bemisia tabaci and affect approximately half of all cassava plants in Africa, resulting in annual production losses of more than $US 1 billion. A historical and current bias towards virus rather than vector control means that these diseases continue to spread, and high Bemisia populations threaten future virus spread even if the extant strains and species are controlled. Progress has been made in parts of Africa in replicating some of the successes of integrated Bemisia control programmes in the south-western United States. However, these management efforts, which utilise chemical insecticides that conserve the Bemisia natural enemy fauna, are only suitable for commercial agriculture, which presently excludes most cassava cultivation in Africa. Initiatives to strengthen the control of B. tabaci on cassava in Africa need to be aware of this limitation, and to focus primarily on control methods that are cheap, effective, sustainable and readily disseminated, such as host-plant resistance and biological control. A framework based on the application of force multipliers is proposed as a means of prioritising elements of future Bemisia control strategies for cassava in Africa. © 2014 Society of Chemical Industry.

Mwatawala M.,Sokoine University of Agriculture | Kudra A.,Sokoine University of Agriculture | Mkiga A.,Ukiriguru Agricultural Research Institute | Godfrey E.,Sokoine University of Agriculture | And 3 more authors.
Fruits | Year: 2015

Introduction. Host preference of Zeugodacus cucurbitae in three vegetables was determined under choice and no-choice experiments. Materials and methods. The experiments were conducted in both semi-natural (under cage) and natural (no cage) field conditions. The trials were run for three seasons between March 2013 and July 2014 in Morogoro Region, Tanzania. In each season, two sets of plots of watermelon Citrullus lanatus, cucumber Cucumis sativus and pumpkin Cucurbita sp., were established in mono and mixed cropping systems. A set of plots was placed under individual cages and another set of plots was left open. Colonies of Z. cucurbitae were regularly established from wild cucurbits and the emerging adults were maintained on artificial diets. The adults were released into cages once in a cropping season, at a sex ratio ratio of 1:1. A total of 60 and 180 adults were released into choice (4 × 4 m) and no choice (4 × 12 m) plots respectively. Open fields were infested naturally. Released adults were between 21 and 30 days old post emergence. Flies were released between six and eight weeks after sowing the vegetables. Fruits were harvested a week after release of flies into cages. Trials were also conducted to determine the dominant cucurbit infester in cucumber. Infestation rates and incidences were determined and used to indicate preference of Z. cucurbitae among the three vegetables. Results and discussion. Highest infestation rate of Z. cucurbitae was recorded in watermelon while lowest in pumpkin. Infestation rates were significantly high in fruits grown under no choice compared to choice plots. More flies emerged from fruits grown in no choice plots. However, infestation rates were not significantly different among fruits from natural and semi-natural conditions. Other cucurbit infesters, Dacus bivittatus, D. frontalis, D. vertebratus and D. ciliatus emerged from fruits grown in open (no cage) field plots. Further results show that Z. cucurbitae dominated Dacus bivittatus and D. frontalis in cucumber. Conclusion. Watermelon is the most preferred host of the dominant cucurbit infester Z. cucurbitae. © Cirad/EDP Sciences 2015.

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