CBN-V Video Archives - S6-17
Classification of Cassava into "Bitter" and "Cool" in Malawi: The Farmers' Method.

Mkumbira J.^{1, 2}, L. Chiwona-Karltun^3,4, U. Lagercrantz², N.M. Mahungu⁵, J. Saka⁶, A. Mhone⁶, M. Bokanga⁷, L. Brimer⁸, U. Gullberg² and H. Rosling³

1. Bvumbwe Agricultural Research Station, P.O. Box 5748, Limbe, Malawi Jonathan.Mkumbira@wbiol.slu.se
2. Department of Plant Biology, Swedish University of Agricultural Sciences, Box 7080, SE-750 05 Uppsala, Sweden
3. Division of International Health, Department of Public Health Sciences, Karolinska Institute, SE-171 76 Stockholm, Sweden
4. Nutrition Unit, Department of Medical Sciences, Uppsala University, Dag Hammarskjölds väg 21, SE-752 37 Uppsala, Sweden Linley.Karltun@Nutrition.uu.se
5. IITA/SARRNET, Chitedze Research Station, Box 30258, Lilongwe 3, Malawi
6. Department of Chemistry, Chancellor College, University of Malawi, Box 280, Zomba, Malawi
7. International Institute for Tropical Agriculture, Oyo Road, P.M.B. 5320, Ibadan, Nigeria
8. Department of Pharmacology and Pathobiology, The Royal Veterinary and Agricultural University, 13 Bülowsvej, DK-1870 Frederiksberg C., Denmark

        All cassava (Manihot esculenta Crantz) plants contain cyanogenic glucosides, with a gradual transition from completely non-poisonous to extremely poisonous. Within cassava farming systems, farmers recognise their cultivars as either being bitter tasting and dangerous or "sweet"/cool tasting and non-dangerous. In Malawi, farmers classify cassava cultivars in similar manner. This paper shows that this classification is based on the differences in cyanogenic glucoside levels and a systematic division into "bitter" and "cool". SSR molecular markers support the findings, while there may be several possible explanations. Farmers’ classification into ‘cool’ and ‘bitter’ cultivars corresponded to a genetic sub-division with four-fold difference in cyanogenic glucoside levels. Farmers were able to distinguish genotypes by carefully examining morphology with some few mistakes. The necessity to differentiate between "bitter" and "cool" cultivars based on cyanogenic glucoside levels seems to have influenced the genetic structure of cassava in this area. These findings have implications for breeding programmes because work is underway to develop cyanogenic glucoside free varieties. Further studies are needed to understand the role of cyanogenesis in cassava farming systems.

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