GENETIC STRUCTURE OF HORDEUM JUBATUM. I. OUTCROSSING RATES AND HETEROZYGOSITY LEVELS

Abstract

The inheritance patterns of four allozyme systems were studied in the tetraploid weed, Hordeum jubatum L. The allozymes are: two cathodal peroxidase systems, CPX-2 and CPX-6, one glutamate oxaloacetate transaminase system, GOT-2, and one esterase system, EST-4. Using these systems outcrossing rates in two populations were calculated to be 1 to 3%. Because of intensive inbreeding, there is little heterozygosity at any of the loci examined in three sample populations. In the GOT and EST systems, however, duplicated loci resulting from polyploidy produce high levels of fixed heterozygosity. In the EST system, both heterozygous and homozygous phenotypes can occur in high frequencies in a population. The underlying genotypic flexibility may be the result of duplicated loci segregating for the same alleles, or for null alleles. The combination of self-fertilization, polyploidy, and duplicated loci with genotypic flexibility may contribute to the successful weedy nature of H. jubatum.