CBN-V Video Archives - S4-02
Genetic Differentiation in Cassava (Manihot esculenta) Land Races as Assessed by Simple Sequence Repeat (SSR) Markers

Fregene M¹., M. Suarez¹., J. Mkumbira.², H. Kulembeka.³, E. Ndedya. ⁴, A. Kulaya.⁵, S. Mitchel⁷, U. Gullberg², H. Rosling⁶, A. Dixon⁷ and S. Kresovich⁸.

1. International Center for Tropical Agriculture (CIAT), Cali, Colombia
m.fregene@cgiar.org
2. Swedish Agricultural University (SLU), Uppsala, Sweden
3. Agricultural Research Institute (ARI), Mwanza, Tanzania
4. Rural Integrated Project Support Programs (RIPs), Mtwara. Tanzania
5. Agricutural Research Institute, Mikocheni, Dar es Salam, Tanzania
6. Division of International Health, Department of Public Health Sciences, Karolinska Institute, SE-171 76, Stockholm, Sweden
7. International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria
8. Institute for Genome Diversity (IGD), Cornell University, Ithaca, USA

        SSR diversity was assessed at 67 unlinked loci in 303 accessions of cassava land races from Tanzania, Nigeria, Brazil, Colombia, Peru, Venezuela, Guatemala, Mexico and Argentina. From allele frequencies of each locus and over loci the following statistics were estimated: percentage of polymorphic loci, mean number of alleles, average observed heterozygosity, Ho the average gene diversity, He, and average inbreeding coefficient Fis_p, the total heterozygosity, (Ht) and the proportion of among accession differentiation (GST). Genetic differentiation among the land races grouped by country (samples) was quantified by the F statistics estimator Fst (theta), the fixation index, Fit (CapF), amongst others. Results reveal more than 90% of loci were polymorphic in all samples and estimates of genetic diversity and differentiation ranged widely from locus to locus. Total heterozygosity found was 0.64 while within sample heterozygosity was 0.58. A low level of genetic differentiation was found overall in the cassava land races, only about 10% of the genetic diversity are among samples (country groupings). Factors that contribute to differences in allele frequency at SSR loci in this predominantly vegetatively propagated crop appears to be spontaneous recombination, as assessed by parent-offspring relationships, and selection.

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