Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2005
Publication Date: January 1, 2006
Citation: Jensen, K.B., Larson, S.R., Waldron, B.L., Asay, K.H. 2006. Cytogenetics and molecular characterization of hybrids between 6x, 4x, and 2x ploidy levels in crested wheatgrass. Crop Science 46: 105-112. 2006 Interpretive Summary: Crested wheatgrass has been an important range grass used to improve semiarid rangelands of western North America. It is credited with salvaging vast acres of deteriorated rangelands and abandoned cropland during the depression and 'dustbowl' period of the 1930's. Typical crested wheatgrass has 28 chromosomes, is drought tolerant; however, its forage quality declines rapidly after heading. Found within the National Plant Germplasm System (NPGS), was a crested wheatgrass collection that had 42 chromosomes and with leaves that were much wider and maintained their green color and quality several weeks longer in the growing season that typical crested wheatgrass. This 42 chromosome collection was not as drought tolerant as the 28 chromosome crested wheatgrasses. This study describes the development of hybrids between the 28 and 42 chromosome collections, chromosome pairing in the hybrids, molecular association, and transmission of the broadleaf trait into a 28 chromosome breeding population. We were able to establish a fertile 28 chromosome breeding population that combines the drought tolerance of the 28 chromosome crested wheatgrass with the wide leaf characteristic of the 42 chromosome plant.
Technical Abstract: The crested wheatgrass cultivar Hycrest, which consists of germplasm from diploid (2n=2x=14) Agropuron cristatum (L.) Gaertn. and tetraploid (2n=4x=28) 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 and the progeny had varying levels of fertility. Chromosome pairing in this hybrid was irregular and chromosome numbers ranged from 2n=27 to 41. Leaf morphology in the Hycrest x 6x-BL, F1 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, and then crossed among themselves [(Hycrest x 6x-BL) x (Hycrest x 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 the [(Hycrest x 6x-BL) x (Hycrest x 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.