Complex interspecific hybridization in barley (Hordeum vulgare L.) and the possible occurrence of apomixis

Several complex hybrids were produced from the combination [(Hordeum lechleri, 6x xH. procerum, 6 x) × H. vulgare, 2 x]. Crosses with six diploid barley lines resulted in triple hybrids, most of which had a full complement of barley chromosomes (no. 1-7), but were mixoploid with respect to alien chromosomes (19-22). In one combination, chromosome no. 7 was duplicated. Meiosis in triple hybrids showed low, but variable pairing (1.3-5.5 chiasmata per cell). The syndesis probably did not include the barley chromosomes. Direct back-crosses to di- and tetraploid barley lines were unsuccessful. Chromosome doubling of the triple hybrid based on cv 'Pallas' resulted in a plant with 2n = 53-56, which had an increased fertility. Backcrosses to one di- and one tetraploid barley line resulted in offspring. The cross made with the tetraploid line ('Haisa II'), produced a 28-chromosomic plant in which the male parental genome was absent. We suspect that this plant may have arisen through parthenogenetic development of a reduced female gamete. The other cross with a diploid line ('9208/9') resulted in plant with 2n = 51-53. The most likely explanation for this second plant is that an unreduced gamete from the amphiploid was fertilized by a normal gamete from the backcross parent, and during early embryo development, some chromosomes were eliminated.