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

Abstract

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.

Differences in Manioc Diversity Among Five Ethnic Groups of the Colombian Amazon

“…The sequences obtained from each manioc landrace through its genetic analysis were read, organized and analyzed to obtain the genetic structure of the population of the samples collected. The genetic structure was obtained using a Bayesian model approach [81] with the STRUCTURE 2.2 software [82]. This Bayesian analysis determines the minimum number of populations (K) that could have generated the observed diversity using an admixture model and assumes that each individual inherited some portion of its ancestry from each one of the K populations determined.…”

QTL Mapping for Pest and Disease Resistance in Cassava and Coincidence of Some QTL with Introgression Regions Derived from Manihot glaziovii

“…The F 1 progeny were first screened to detect off types and selfs using 12 SSR markers (Kawuki et al, 2013) that were identified as being polymorphic between the two parents. Genotyping by sequencing (GBS) (Elshire et al, 2011) was performed on the confirmed progeny at the University of California, Berkeley (ICGMC, 2015).…”

Biochemical factors associated with cassava resistance to whitefly infestation

“…Adult numbers were counted on three randomly selected sub-set of 10 plants per genotype, starting at 82 DAP and, thereafter, at 30 days for four consecutive periods; damage scores were recorded concurrently (Kawuki et al, 2013). Each leaf was held gently and turned upside down to facilitate counting of adult insects during the relatively cooler periods of the day (7.00 am to 10.00 am.)…”