Worldwide patterns of genetic variation among four esterase loci in Barley (Hordeum vulgare L.)

Electrophoretic assays of 1506 accessions of domestic (Hordeum vulgare L.) and wild (H. spontaneum Koch.) barley, maintained in the USDA World Barley Collection, led to the following conclusions: (1) worldwide the four esterase loci, Est 1, Est 2, Est 3, and Est 4, have a minimum of 7, 12, 6, and 7 alleles, respectively; (2) little or no genetic differentation has developed between H. vulgare and H. spontaneum at these four esterase loci; (3) substantial genetic polymorphism and heterozygosity occur within many of the accessions despite the heavy inbreeding which results from the mating system of predominant self fertilization and from genetic drift associated with maintenance in small populations; (4) patterns of geographical distribution of alleles at these four loci are not at random over both small and large geographical areas, including differences on a continental scale; (5) four among 16 four-locus combinations of alleles are found in excess and all other combinations occur in deficiency on a worldwide basis.