Submitted to: The Nucleus
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2007
Publication Date: 2/10/2008
Citation: Dogramaci, M., Jauhar, P.P. 2008. Synthesis of trigeneric hybrids of hexaploid wheat with diploid wheatgrasses: Specificity of chromosome pairing. The Nucleus. 50:491-500. Interpretive Summary: Wild relatives of wheat are excellent reservoirs of genes for superior traits, including resistance to various diseases, such as scab or FHB. Thus, two diploid wheatgrasses with J and E genomes (a “genome” is a set of chromosomes) are important sources of genes for scab resistance. These grasses are therefore potential donors of this resistance into wheat. Through hybridization, we produced trigeneric hybrids with five genomes, combining the two grass genomes J and E with the three wheat genomes A, B and D. Although the chromosome sets of the two grasses were combined with the wheat chromosomes, pairing between the wheat and grass chromosomes is the key to transferring the desired grass genes into wheat. We employed a sophisticated tool, called fl-GISH, to confirm that such pairing had indeed occurred. This pairing became possible because the Ph1 gene of wheat that acts as a “policeman” to control pairing was inactivated by the grass genotype. Pairing between the wheat and grass chromosomes should help alien gene introgression into wheat.
Technical Abstract: Wild grasses in the tribe Triticeae are excellent sources of genes for superior traits, including resistance to various diseases. Diploid wheatgrasses – Lophopyrum elongatum (Host) Á. Löve (2n = 2x = 14; EE genome) and Thinopyrum bessarabicum (Savul. & Rayss) Á. Löve (2n = 2x = 14; JJ genome) – are important sources of Fusarium head blight (FHB) resistance that may be transferred to wheat. Earlier, fertile amphidiploids (2n = 4x = 28; JJEE) were developed from diploid F1 hybrids (2n = 2x = 14; JE) of the two diploid species. By crossing these amphidiploids with the wheat cultivar ‘Fukohokomugi’ we synthesized trigeneric hybrids with five genomes (2n = 5x = 35; ABDJE) combining the grass genomes J and E with the wheat genomes A, B and D. The trigeneric hybrids were perennial, profusely tillering, and vigorous in growth. Although all trigeneric hybrids had the wheat Ph1 gene that suppresses homoeologous chromosome pairing, the hybrids showed extensive pairing, ranging from 59.4 to 70.4% with an average of 64.4% of the complement. Fl-GISH analysis provided an excellent tool for studying the specificity of chromosome pairing, allowing discrimination of wheat–wheat, grass–grass, and wheat–grass chromosome pairing. Homoeologous pairing in the ABD complement (i.e., wheat–wheat pairing) amounted to 60%. It is inferred that the genotype of the grass amphidiploid parent inactivated the Ph1, such that homoeologous pairing induced was comparable to that in wheat euhaploids without Ph1 that we studied earlier. Homoeologous pairing between wheat and grass chromosomes is of interest from the breeding standpoint because such pairing would be essential for alien gene transfer from the grass amphidiploid into wheat.