RESEARCH ARTICLE Molecular differentiation, diversity, and folk classification of ‘‘sweet’’ and ‘‘bitter’’ cassava (Manihot esculenta) in Caic ¸ara and Caboclo management systems (Brazil) Nivaldo Peroni Æ Paulo Yoshio Kageyama Æ Alpina Begossi Received: 9 December 2005 / Accepted: 28 August 2006 / Published online: 10 March 2007 Ó Springer Science+Business Media B.V. 2007 Abstract This study focuses the inter-relation- ships among the men, the use, and the intra- specific cassava diversity, under the perspective of this crop evolutionary dynamics. The origin, the use and the current local management of varieties with high and low cyanogenic potential are important questions around cassava domestica- tion. We collected 169 local varieties identified as ‘‘sweet’’ or ‘‘bitter’’ cassava by traditional farmers from Atlantic Forest and Amazon (Medium Negro River Basin), Brazil. Using a population genetics and an ethnobotany approach, the diver- sity and the genetic structure of cassava were evaluated. We found a total of 115 vernacular names, and in the Atlantic Forest sample the average genetic diversity (H S = 0.654) was higher for the sweet varieties than for bitter ones (0.582). The genetic differentiation coefficient (R ST ), used to estimate the diversity among groups, was 0.057 (P < 0.001), indicating that the divergence between the two groups is low. We obtained a low correlation between the morphological and genetic distances, and the congruence was high when the ethnoclassification and the genetic structure were considered. We discuss the adap- tive advantages of the sweet varieties use, the current socio-economic changes in bitter varieties use, and the ecological history of these variety groups. Keywords Atlantic Forest Á Bitter cassava Á Caboclos Á Caic ¸aras Á Manihot esculenta Crantz Á Sweet cassava Introduction The cassava (Manihot esculenta Crantz ssp. esculenta) was domesticated at the South Amer- ica lowlands 7,000 years ago at least, and it has been still considered as one of the main crops for the Amerindians and a traditional species in Brazil (Allem 1994; Olsen and Schall 1999). The study of its botanical and ecological origin has been fomented by the understanding of human actions related to the species domestication, and to the factors that proportionate, along the time, the amplification of its intra-specific diversity (Boster 1985; Olsen and Schall 1999; Peroni and N. Peroni (&) Á A. Begossi Biology Institute, Natural History Museum, UNICAMP, CP 6109, Campinas, SP CEP 13084-971, Brazil e-mail: nivaldo@unicamp.br A. Begossi e-mail: alpina@unicamp.br P. Y. Kageyama Forest Science Department, Escola Superior de Agricultura ‘‘Luiz de Queiroz’’, ESALQ/USP, Piracicaba, SP, Brazil e-mail: kageyama@esalq.usp.br 123 Genet Resour Crop Evol (2007) 54:1333–1349 DOI 10.1007/s10722-006-9116-2