Cytogenetic and Molecular Characterization of Hybrids between 6 x , 4 x , and 2 x Ploidy Levels in Crested Wheatgrass

The crested wheatgrass cultivar ‘Hycrest,’ which consists of germplasm from an induced tetraploid of Agropuron cristatum (2 n = 4 x = 28) (L.) Gaertn. and a natural tetraploid (2 n = 4 x = 28) of A. desertorum (Fisch. Ex Link) Schultes, was hybridized with a promising broadleaf hexaploid (6 x ‐BL; 2 n = 6 x = 42) accession of A. cristatum from the USSR. The goal was to combine the wide leaf characteristic and green color retention from the 6 x ‐BL parent into a common gene pool. The crossability between Hycrest (4 x ) and 6 x ‐BL (6 x ) was excellent; however, chromosome pairing was irregular and chromosome numbers ranged from 2 n = 27 to 41. Leaf morphology in Hycrest/6 x ‐BL hybrids was intermediate to that of the parents. Selected F 1 pentaploid progenies (2 n = 5 x = 35), with leaf widths approaching that of the 6 x ‐BL parent, were backcrossed to Hycrest (Hycrest*2/6 x ‐BL), and then crossed among themselves (Hycrest*2/6 x ‐BL//Hycrest*2/6 x ‐BL). In the backcross hybrid, chromosome numbers ranged from 2 n = 28 to 39. Meiotically, 28 chromosome backcross hybrid plants were more stable than aneuploid backcross hybrids. The broadleaf character was readily detected in the backcross progeny. In Hycrest/6 x ‐BL//Hycrest/6 x ‐BL hybrids, chromosome numbers ranged from 2n = 33 to 45. Despite the hybrid origin, all aneuploid hybrids had an increased number of univalents and chromosome associations that involved more than four chromosomes. AFLP analysis reflected genetic introgression from the 6 x ‐BL parent beyond that observed in Hycrest. Results support earlier conclusions that the crested wheatgrass complex should be treated as a common gene pool.