Microsatellite variation in cassava (Manihot esculenta, Euphorbiaceae) andits wild relatives: Further evidence for a southern Amazonian origin of domestication

Genetic variation at five microsatellite loci was used to investigate the e volutionary and geographical origins of cassava (Manihot esculenta subsp. e sculenta) and the population structure of cassava's wild relatives. Two hun dred and twelve individuals were sampled, representing 20 crop accessions, 27 populations of cassava's closest wild relative (M. esculenta subsp. flab ellifolia), and six populations of a potentially hybridizing species (M. pr uinosa). Seventy-three alleles were observed across all loci and population s. These data indicate the following on cassava's origin: (1) genetic varia tion in the crop is a subset of that found in the wild M. esculenta subspec ies, suggesting that cassava is derived solely from its conspecific wild re lative. (2) Phenetic analyses group cassava with wild populations from the southern border of the Amazon basin, indicating this region as the likely s ite of domestication. (3) Manihot pruinosa, while closely related to M. esc ulenta (and possibly hybridizing with it where sympatric), is probably not a progenitor of the crop. Genetic differentiation among the wild population s is moderately high (F-ST = 0.42, rho (ST) = 0.54). This differentiation h as probably arisen primarily through random genetic drift (rather than muta tion) following recent population divergence.