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

Genetic variation at five microsatellite loci was used to investigate the evolutionary and geographical Aorigins of cassava (Manihot esculenta subsp. esculenta) and the population structure of cassavaʹs wild relatives. Two hundred and twelve individuals were sampled, representing 20 crop accessions, 27 populations of cassavaʹs closest wild relative (M. esculenta subsp. flabellifolia), and six populations of a potentially hybridizing species (M. pruinosa). Seventy-three alleles were observed across all loci and populations. These data indicate the following on cassavaʹs origin: (1) genetic variation in the crop is a subset of that found in the wild M. esculenta subspecies, suggesting that cassava is derived solely from its conspecific wild relative. (2) Phenetic analyses group cassava with wild populations from the southern border of the Amazon basin, indicating this region as the likely site of domestication. (3) Manihot pruinosa, while closely related to M. esculenta (and possibly hybridizing with it where sympatric), is probably not a progenitor of the crop. Genetic differentiation among the wild populations is moderately high (FST = 0.42, (rho)ST = 0.54). This differentiation has probably arisen primarily through random genetic drift (rather than mutation) following recent population divergence.