Phylogenetic relationships of sorghum taxa inferred from mitochondrial DNA restriction fragment analysis

To elucidate the evolutionary history and affinity of sorghum species, 41 sorghum taxa were analyzed using variability in mitochondrial DNA. Analysis of species relationships at the molecular level can provide additional data to supplement the existing classification based on morphological characters and may also furnish unexpected but useful information. Total DNA extracted from each of the sorghum accessions was digested with each of five restriction enzymes, BamHI, HindIII, EcoRI, EcoRV, and XbaI, and probed with five mitochondrial DNAs cloned from Sorghum bicolor. A total of 180 restriction fragments was detected by the 25 probe-enzyme combinations. Forty-three fragment bands were phylogenetically informative. Multiple correspondence analysis was performed to visualize associations among the accessions and suggested that section Eusorghum species may be divided into four groups, with Sorghum laxiflorum (section Heterosorghum) and Sorghum nitidum (section Parasorghum) appearing as outliers. A phylogenetic tree was assembled from mitochondrial restriction fragment data. The taxa analyzed formed three major groups comprising section Heterosorghum (group D, section Parasorghum (group II), and all accessions in section Eusorghum (group III). Group III is further divided into four groups: (i) two sweet sorghums and shattercane; (ii) Sorghum halepense, Sorghum miliaceum, Sorghum hewisonii, Sorghum aethiopicum, Sorghum verticilliflorum, and S. bicolor, including Sorghum sudanense (sudangrass), the Chinese Kaoliangs, and a number of commercial sorghum inbreds from the U.S.A.; (iii) Sorghum propinquum; and (iv) Sorghum arundinaceum, Sorghum niloticum, Sorghum almum, Sorghum controversum, and the Chinese material C-401 and 5-27. Results indicate that the analysis of fragmented mitochondrial DNA was diagnostic and useful in sorghum phylogenetic and taxonomic research at the species, subspecies, and race levels, and can complement results from those analyses using nuclear ribosomal DNA and chloroplast DNA that effectively distinguish taxa at species and genus levels.