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CROP BREEDING, GENETICS & CYTOLOGY

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

USDA-ARS, Forage and Range Research Laboratory, Utah State Univ., Logan, UT 84322-6300. USA. Cooperative investigations of the USDA-ARS and the Utah Agric. Exp. St., Logan, UT 84322.

^* Corresponding author (kevin{at}cc.usu.edu)

The crested wheatgrass cultivar ‘Hycrest,’ which consists of germplasm from an induced tetraploid of Agropuron cristatum (2n = 4x = 28) (L.) Gaertn. and a natural tetraploid (2n = 4x = 28) of A. desertorum (Fisch. Ex Link) Schultes, was hybridized with a promising broadleaf hexaploid (6x-BL; 2n = 6x = 42) accession of A. cristatum from the USSR. The goal was to combine the wide leaf characteristic and green color retention from the 6x-BL parent into a common gene pool. The crossability between Hycrest (4x) and 6x-BL (6x) was excellent; however, chromosome pairing was irregular and chromosome numbers ranged from 2n = 27 to 41. Leaf morphology in Hycrest/6x-BL hybrids was intermediate to that of the parents. Selected F₁ pentaploid progenies (2n = 5x = 35), with leaf widths approaching that of the 6x-BL parent, were backcrossed to Hycrest (Hycrest*2/6x-BL), and then crossed among themselves (Hycrest*2/6x-BL//Hycrest*2/6x-BL). In the backcross hybrid, chromosome numbers ranged from 2n = 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/6x-BL//Hycrest/6x-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 6x-BL parent beyond that observed in Hycrest. Results support earlier conclusions that the crested wheatgrass complex should be treated as a common gene pool.

Abbreviations: AMOVA, analysis of molecular variance • AFLP, amplified fragment length polymorphism • UPGMA, unweighted pair group method with arithmetic averages