CBN-V Video Archives - PS2-02
Genetic Resources and Germplasm Conservation in the Genus Manihot

Schaal B.A.

Department of Biology, Washington University St. Louis, MO 63130, USA schaal@biology.wustl.edu

        The phylogenetic relationships among species of the genus Manihot have been actively debated. Resolution of species affinities is of critical importance since the domesticated species, Manihot esculenta ssp. esculenta Kranz, cassava, provides an important source of carbohydrates for people throughout the tropics. We have investigated the species relationships within the genus Manihot by a molecular phylogeny reconstruction and by an analysis of RAPD data. Gene sequences used for phylogeny reconstruction include the ITS-1 and ITS-2 regions of nuclear ribosomal DNA, calmodulin, linamarase, and aspartate amino transferase. DNA analysis indicates a South American origin for cassava with M. esculenta ssp. flabellifolia as well as several other species being close wild relatives. Several gene sequences are identical among these species and cassava, indicating close affinities and most likely, a recent common ancestor. A phylogeographic study of wild M. esculenta ssp. flabellifolia populations using haplotype analysis for several genes as well as microsatellite markers indicate a very close association between cassava and wild populations on the southern border of the Cerrado and Amazon forest interface. Many questions remain about the systematic relationships within the genus Manihot as well as the role of hybridization in the domestication of cassava. Addressing these issues is of high priority so that appropriate taxa and populations can be identified for germplasm collection and preservation.

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