Patterns of allozyme variation in cultivated and wild Sorghum bicolor

Patterns of allozyme variation were surveyed in collections of cultivated and wild sorghum from Africa, the Middle East, and Asia. Data for 30 isozyme loci from a total of 2067 plants representing 429 accessions were analyzed. Regional levels of genetic diversity in the cultivars are greater in northern and central Africa compared to southern Africa, the Middle East, or Asia. The spatial distribution of individual alleles at the most variable loci was studied by plotting allele frequencies on geographic maps covering the distribution of sorghum. Generally, many of the alleles with frequencies below 0.25 are localized in specific portions of the range and are commonly present in more than one race in that region. Several alleles occur in both wild and cultivated sorghum of one region and are absent from sorghum elsewhere, suggesting local introgression between the wild and cultivated forms. Although the same most common allele was found in the wild and cultivated gene pools at 29 of the 30 loci, phenetic analyses separated the majority of wild collections from the cultivars, indicating that the two gene pools are distinct. Wild sorghum from northeast and central Africa exhibits greater genetic similarities to the cultivars compared to wild sorghum of northwest or southern Africa. This is consistent with the theory that wild sorghum of northeast-central Africa is ancestral to domesticated sorghum. Wild sorghums of race arundinaceum of northwest Africa and race virgatum from Egypt are shown to be genetically distinct from both other forms of wild sorghum and from the cultivars. Suggestions for genetic conservation are presented in light of these data.