ISOZYMES OF ELEUSINE (GRAMINEAE) AND THE ORIGIN OF FINGER MILLET

The predominantly African grass genus Eleusine comprises nine species, including diploids and tetraploids based on n = 8, 9, and 10. Among t he polyploids are the important crop finger millet, Eleusine coracana subsp. coracana, and its putative wild ancestor, E. coracana subsp. af ricana. Eleusine coracana is believed to be an allotetraploid derived by hybridization between E. indica and an unknown diploid. To evaluate this hypothesis, 16 isozyme loci coding nine enzymes were compared am ong seven of the nine Eleusine species (E. intermedia and E. semisteri lis were unavailable). Genetic variability differed substantially amon g diploid species, ranging from P = 0.563, A = 1.6, H = 0.208 in E. in dica to P = 0.188, A = 1.2, H = 0.042 in E. jaegeri. The diploids tend ed to be genetically distinct, with values of Rogers' Similarity rangi ng from S = 0.294 (E. jaegeri/floccifolia) to S = 0.794 (E. indica/tri stachya). Both subspecies of the tetraploid E. coracana exhibited fixe d heterozygosity at several loci, verifying their hypothesized allotet raploid status. Both tetraploids also possessed E. indica marker allel es at all loci, corroborating ancestry by this taxon. Genotypes of the non-indica ancestor, inferred separately for each tetraploid, differe d substantially from all candidate diploids and also from each other. These data indicate that 1) none of the candidate diploids investigate d is likely to have been the non-indica ancestor of E. coracana, and 2 ) the non-indica ancestor of the wild tetraploid may differ from that of the crop. The latter conclusion is inconsistent with the complete c hromosomal homology exhibited between the two tetraploid subspecies, i ndicating the need for additional evidence bearing on their relationsh ips.