Maintenance of Manioc Diversity by Traditional Farmers in the State of Mato Grosso, Brazil: A 20-Year Comparison. Few studies discuss agrobiodiversity in the Brazilian savanna, which is believed to be the geographical origin of manioc and is one of its centers of diversity. Using an ethnobotanical approach, we evaluated the varieties of manioc cultivated by traditional farmers in the region, comparing two years: 1992 and 2011. Participant observation and semistructured interviews were conducted in both years in the same communities-27 farms in 1992 and 30 in 2011. Area of cultivated land was measured, all the manioc varieties identified by the farmers were inventoried in the fields, and the crop density was estimated. Diversity was similar for both years (1992: 60 varieties, H' = 1.53; 2011: 54 varieties, H' = 1.52); however, the mean number of varieties per farmer decreased from 9.4 +/- 4.5 to 5.4 +/- 4.4. The frequency and abundance of the varieties also changed. Varieties that were uncommon or nonexistent in 1992 were found to be common and occupying larger crop areas in 2011, and vice versa. Agricultural activity has decreased considerably; the mean size of cultivated areas has been reduced by two-thirds, and the majority of young people are not engaged in agricultural activities at all or only part-time. These findings point to serious threats to local agrobiodiversity and the need to discuss ways to maintain it.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Estadual Paulista, Dept Ecol, Inst Biociencias, Sao Paulo, BrazilUniv Sao Paulo, Dept Ciencias Exatas, Escola Super Agr Luiz de Queiroz, Sao Paulo, BrazilUniv Estadual Paulista, Dept Ecol, Inst Biociencias, Sao Paulo, BrazilFAPESP: 08/03822-32010/12181-1