Sorghum domestication and diversification: A current archaeobotanical perspective

Abstract

Sorghum bicolor, one of the world’s five most important crops, originated in Africa. While this has long been clear, accumulating data from both archaeobotany and genetics, provides the basis for a new overview on the domestication process, racial evolution, and geographical dispersal of sorghum. Archaeobotanical finds from 113 sites in Africa and Eurasia are reviewed and mapped. Of these only 16 provide identifications of probable morphological races. Domestication is evidently taking place more than 3000 years BC in the eastern Sudan near the Atbara and Gash rivers. Early domesticated race bicolor then spread to South Asia around 2000 BC and to the Niger Basin in West Africa after 1000 BC. The framework of five cultivated races remains useful, with the original domesticated race bicolor being characterized by tight-fitting hulls requiring dehusking and the other races representing subsequent parallel evolution for free-threshing and larger-grained cultivars. This took place at least three times, including race ‘caudatum’ focused initially on the Sahelian region race ‘durra’ that evolved probably in India, and race ‘guinea’ that evolved in forested West Africa. Early race guinea in turn produced an even more forest adapted ‘mageritiferum’ type that appears to be ancestral to southern African guinea and ‘kafir’ sorghums, implying a dispersal across the central African rainforests. In contrast other eastern African caudatums and ‘bicolor’ types presumably followed a savannah dispersal. In addition to the early dispersal of race bicolor from Africa to India, which was ancestral to East Asian sorghums, a later dispersal of guinea types is inferred to have taken place from southeastern Africa across the Indian Ocean.