Mitochondrial DNA diversity in wild and cultivated sorghum

Cultivated sorghum (Sorghum bicolor ssp. bicolor) is classified into five main races on the basis of spikelet morphology. Isozyme analyses provided new insight into the genetic diversity of sorghum and revealed marked geographic grouping, while nuclear restriction fragment length polymorphisms showed racial differentiation and intraguinea race differentiation. Wild sorghum is diploid or tetraploid and African sorghum (S. bicolor ssp. arundinaceum) is classified into four races, that are considered to be progenitors of cultivated sorghum. We performed mitochondrial DNA analyses to compare the diversity of wild and cultivated sorghum and to study the genetic origin of guinea margaritiferum. The same overall patterns were obtained with the different phenogram construction techniques. Our results confirmed the specificity of guinea margaritiferum and demonstrated the presence of two genetic entities within this subrace. Another guinea group was also noted, which corresponded to Asian guinea roxburghii. In wild sorghum, the arundinaceum race appeared to be homogenous, while the verticilliflorum race was separated into two groups, one of which was associated with the arundinaceum race. The diversity observed in cultivated forms was found to be encompassed within the wild pool, except for one guinea margaritiferum group. There did not seem to be any particular relationship between wild races and cultivated races.