Genomic prediction and quantitative trait locus discovery in a cassava training population constructed from multiple breeding stages

Open Access Article; Published online: 11 Dec 2019Assembly of a training population (TP) is an important component of effective genomic selection‐based breeding programs. In this study, we examined the power of diverse germplasm assembled from two cassava (Manihot esculenta Crantz) breeding programs in Tanzania at different breeding stages to predict traits and discover quantitative trait loci (QTL). This is the first genomic selection and genome‐wide association study (GWAS) on Tanzanian cassava data. We detected QTL associated with cassava mosaic disease (CMD) resistance on chromosomes 12 and 16; QTL conferring resistance to cassava brown streak disease (CBSD) on chromosomes 9 and 11; and QTL on chromosomes 2, 3, 8, and 10 associated with resistance to CBSD for root necrosis. We detected a QTL on chromosome 4 and two QTL on chromosome 12 conferring dual resistance to CMD and CBSD. The use of clones in the same stage to construct TPs provided higher trait prediction accuracy than TPs with a mixture of clones from multiple breeding stages. Moreover, clones in the early breeding stage provided more reliable trait prediction accuracy and are better candidates for constructing a TP. Although larger TP sizes have been associated with improved accuracy, in this study, adding clones from Kibaha to those from Ukiriguru and vice versa did not improve the prediction accuracy of either population. Including the Ugandan TP in either population did not improve trait prediction accuracy. This study applied genomic prediction to understand the implications of constructing TP from clones at different breeding stages pooled from different locations on trait accuracy

Pasting properties of high-quality cassava flour of some selected improved cassava varieties in Tanzania for baking

Open Access ArticlePartial substituting wheat with high-quality cassava flour (HQCF) in bread making would be economically beneficial in Tanzania. However, cassava varieties with the best pasting quality for this use are unknown. In addition, the appropriate time of harvesting the varieties to attain the best pasting quality is also unknown. This study, therefore, aimed at identifying the most appropriate cassava varieties and their appropriate harvesting time that could be used for production of HQCF for baking bread. Nine improved cassava varieties namely Kiroba, Mkuranga1, Pwani, Chereko, Mkumba, Hombolo, Orela, Kizimbani and Kipusa and two local varieties, Albert and Kibandameno were planted in 2020/2021 and 2021/2022 seasons at TARI-Ukiriguru using a split plot design. Harvesting was done at 10 and 12 months after planting (MAP). Pasting characteristics of the HQCF samples were determined at the International Centre of Tropical Agriculture, Dar es salaam, Tanzania using Perten Rapid Visco Analyzer (RVA) Tecmaster equipment, Model: N103802. The results indicated that KIPUSA had the lowest significant setback, while Hombolo had the highest significant setback both at 10 and 12 MAP suggesting that HQCF produced from KIPUSA should be considered for partial substitution of wheat in baking bread that is attractive to consumers

QTL associated with resistance to cassava brown streak and cassava mosaic diseases in a bi-parental cross of two Tanzanian farmer varieties, Namikonga and Albert

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.The Bill and Melinda Gates Foundation for funding under Contract ID OPPGD1016.http://www.sherpa.ac.uk/romeo/issn/0040-5752/am2017Forestry and Agricultural Biotechnology Institute (FABI)Genetic

Genotype by environment cultivar evaluation for cassava brown streak disease resistance in Tanzania

Open Access Article; Published online: 24 May 2020Cassava brown steak disease (CBSD), caused by Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), is the most important biotic constraint to cassava production in East and Central Africa. Concerted efforts are required to prevent further spread into West Africa as well as to reduce losses in areas already affected. The study reported here was part of a five-country (Kenya, Malawi, Mozambique, Tanzania and Uganda) programme that aimed to identify superior cassava cultivars resistant to CBSD and to disseminate them widely in the region. Seventeen tissue-cultured and virus-tested cultivars were evaluated in Tanzania across nine sites with diverse CBSD inoculum conditions. Experiments were planted using an alpha-lattice design and assessments were made of surrounding inoculum pressure, CBSD foliar and root incidence and root yield at harvest. There were large differences in CBSD infection between sites, with greatest spread recorded from the north-western Lake (Victoria) zone. Differences were driven by Bemisia tabaci whitefly vector abundance and CBSD inoculum pressure. Both CBSV and UCBSV were almost equally represented in cassava fields surrounding experimental plots, although CBSV predominated in the north-west whilst UCBSV was more frequent in coastal and southern sites. However, the incidence of CBSV was much greater than that of UCBSV in initially virus-free experimental plots, suggesting that CBSV is more virulent. Cultivars could be categorised into three groups based on the degree of CBSD symptom expression in shoots and roots. The seven cultivars (F10_30R2, Eyope, Mkumba, Mkuranga1, Narocass1, Nase3 and Orera) in the most resistant category each had shoot and root incidences of less than 20%. Fresh root yield differed between sites and cultivars, but there was no genotype by environment interaction for this trait, probably attributable to the large fertility and soil moisture differences between sites. Susceptible cultivars and the local check performed well in the absence of CBSD pressure, highlighting the importance of exploiting quality and yield traits of local landraces in breeding programmes. Overall, our results emphasized the importance of applying a balanced strategy for CBSD management. This should use both improved and local germplasm resources to generate high yielding cultivars for specific end-user traits, and combine the deployment of improved cultivars with phytosanitary control measures including the use of healthy planting material and planting during periods of reduced CBSD infection

Collection, genotyping and virus elimination of cassava landraces from Tanzania and documentation of farmer knowledge

Open Access Journal; Published online: 17 Aug 2021Cassava (Manihot esculenta Crantz.) has been a vital staple and food security crop in Tanzania for several centuries, and it is likely that its resilience will play a key role in mitigating livelihood insecurities arising from climate change. The sector is dominated by smallholder farmers growing traditional landrace varieties. A recent surge in virus diseases and awareness in the commercial potential of cassava has prompted a drive to disseminate improved varieties in the country. These factors however also threaten the existence of landraces and associated farmer knowledge. It is important that the landraces are conserved and utilized as the adaptive gene complexes they harbor can drive breeding for improved varieties that meet agro-ecological adaptation as well as farmer and consumer needs, thereby improving adoption rates. Here we report on cassava germplasm collection missions and documentation of farmer knowledge in seven zones of Tanzania. A total of 277 unique landraces are identified through high-density genotyping. The large number of landraces is attributable to a mixed clonal/sexual reproductive system in which the soil seed bank and incorporation of seedlings plays an important role. A striking divergence in genetic relationships between the coastal regions and western regions is evident and explained by (i) independent introductions of cassava into the country, (ii) adaptation to prevailing agro-ecological conditions and (iii) farmer selections according to the intended use or market demands. The main uses of cassava with different product profiles are evident, including fresh consumption, flour production, dual purpose incorporating both these uses and longer-term food security. Each of these products have different trait requirements. Individual landraces were not widely distributed across the country with limited farmer-to-farmer diffusion with implications for seed systems

Participatory evaluation of improved sweetpotato varieties in Eastern Tanzania

Sweetpotato (Ipomoea batatas L.) is among the important subsistence food crops in eastern Tanzania. Sweetpotato is regarded as a food security crop since it bridges a hunger gap when cereals are still in the field. Recently, the crop has been commercialised and is a cash earner. On-farm trials were established in three villages in three districts of Coast and Dar-es-salaam regions. The villages are Pangani (Kibaha), Chanika (Ilala) and Matimbwa (Bagamoyo). Seven varieties were evaluated including 5 officially released varieties Jitihada, Vumilia, Mavuno, Sinia and Simama. Two local improved varieties, Carrot-C (orange-fleshed) and Ukerewe, were also included. The released varieties, with exception of Simama, were tested in the Lake zone of Tanzania only, prior to their release. Participatory variety evaluation involving researchers, extensionists and farmers was adopted in two consecutive seasons. Formal evaluation by researchers proved that a purple skinned and cream fleshed (with orange pigments) variety Ukerewe has generally high establishment, partial resistance to sweetpotato mosaic virus disease and sweetpotato weevils (Cylas spp.). Farmers' assessment revealed the variety to be most preferred by producers and traders. Its purple skin colour increases its market value. Root yield, marketability, resistance to drought, pests and diseases were the main criteria used by farmers in the selection of sweetpotato varieties. Key Words: Ipomea batatus, mosaic virus, orange fleshed, weevil RÉSUMÉ La patate douce (Ipomea batatas L.) est un important aliment de subsistance dans l'Est de la Tanzanie. Elle est vue comme l'aliment assurant la sécurité alimentaire quand les céréales sont encore dans les champs. Récemment, la plante a été commercialisée et devenue une source de revenue. Des expériences sur ferme étaient établies dans trois villages de trois districts de la cote et de Dar-es-Salaam. Ces villages sont Pangani (Kibaha), Chanika (Ilala) et Matimbwa (Bagamoyo). Sept variétés étaient évaluées dont cinq officiellement larguées: Jitihada, Vumilia, Mavuno, Sinia et Simama. Deux variétés locales améliorées, carrot-C (orange graissé) et Ukereme étaient aussi inclues. Les variétés larguées, à l'exception de Simama, étaient testées dans la zone du lac Tanganyika avant leur largage. Une évaluation participative des variétés impliquant les chercheurs, des agents de terrain et des fermiers était adoptée pour deux saisons consécutives. Une évaluation, formelle par les chercheurs montra que les variétés à peau violette et crème graissée (avec des pigments orangés) a généralement un haut niveau d'établissement, une résistance partielle au virus mosaïque et des charançons de la patate douce (Cylas spp.). L'évaluation des fermiers a révélé que la variété est préférée par les producteurs et les vendeurs. La couleur violette de sa peau augmenta sa valeur commerciale. Le rendement des racines, la possibilité d'être commercialisé, sa résistance au déficit en eau, les pestes et les maladies étaient les critères utilisés par les fermiers dans la sélection des variétés de la patate douce. Mots clés: Ipomea batatas, virus mosaïque, orange graissé, charançon African Crop Science Journal Vol.12(3) 2004: 259-26

Simple sequence repeat marker diversity in cassava landraces: genetic diversity and differentiation in an asexually propagated crop

Cassava (Manihot esculenta) is an allogamous, vegetatively propagated, Neotropical crop that is also widely grown in tropical Africa and Southeast Asia. To elucidate genetic diversity and differentiation in the crop's primary and secondary centers of diversity, and the forces shaping them, SSR marker variation was assessed at 67 loci in 283 accessions of cassava landraces from Africa (Tanzania and Nigeria) and the Neotropics (Brazil, Colombia, Peru, Venezuela, Guatemala, Mexico and Argentina). Average gene diversity (i.e., genetic diversity) was high in all countries, with an average heterozygosity of 0.5358 ± 0.1184. Although the highest was found in Brazilian and Colombian accessions, genetic diversity in Neotropical and African materials is comparable. Despite the low level of differentiation [Fst(theta) = 0.091 ± 0.005] found among country samples, sufficient genetic distance (1-proportion of shared alleles) existed between individual genotypes to separate African from Neotropical accessions and to reveal a more pronounced substructure in the African landraces. Forces shaping differences in allele frequency at SSR loci and possibly counterbalancing successive founder effects involve probably spontaneous recombination, as assessed by parent-offspring relationships, and farmer-selection for adaptation

Simple sequence repeat marker diversity in cassava landraces: Genetic diversity and differentiation in an asexually propagated crop

Cassava (Manihot esculenta) is an allogamous, vegetatively propagated, Neotropical crop that is also widely grown in tropical Africa and Southeast Asia. To elucidate genetic diversity and differentiation in the crop's primary and secondary centers of diversity, and the forces shaping them, SSR marker variation was assessed at 67 loci in 283 accessions of cassava landraces from Africa (Tanzania and Nigeria) and the Neotropics (Brazil, Colombia, Peru, Venezuela, Guatemala, Mexico and Argentina). Average gene diversity (i.e., genetic diversity) was high in all countries, with an average heterozygosity of 0.5358 ± 0.1184. Although the highest was found in Brazilian and Colombian accessions, genetic diversity in Neotropical and African materials is comparable. Despite the low level of differentiation [Fst(theta) = 0.091 ± 0.005] found among country samples, sufficient genetic distance (1-proportion of shared alleles) existed between individual genotypes to separate African from Neotropical accessions and to reveal a more pronounced substructure in the African landraces. Forces shaping differences in allele frequency at SSR loci and possibly counterbalancing successive founder effects involve probably spontaneous recombination, as assessed by parent-offspring relationships, and farmer-selection for adaptation

Molecular marker-assisted selection for starchy staples

<p>Tree A was inferred for the region defined by positions 1–219 & 721–1496. Tree B was inferred for the region defined by positions 220–720. ML trees inferred with PAUP* have identical topology to the trees shown here. Phylogenetic relationships in these trees do not support a hypothesis of homologous recombination. Other features as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010434#pone-0010434-g001" target="_blank">Figure 1</a>.</p