Submitted to: Genome
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/30/2004
Publication Date: 12/25/2004
Citation: Jauhar, P.P., Dogramaci, M., Peterson, T.S. 2004. Synthesis and cytological characterization of trigeneric hybrids of durum wheat with and without ph1. Genome. Vol 47(6)1173-1181. Interpretive Summary: Wild grasses in the wheat tribe Triticeae, closely or distantly related to wheat, are rich reservoirs of genes for agronomically superior traits, including resistance to various diseases. Diploid wheatgrasses, with the JJ and EE genomes (a genome is a set of chromosomes), are important sources of genes for resistance to serious diseases, such as scab or Fusarium head blight (FHB). Thus, these grasses are potential donors of FHB resistance to wheat. Through a series of crosses, involving durum wheat and the two wheatgrasses, we synthesized hybrids incorporating both the J and E genomes in the durum background. The purpose of transferring both these genomes into durum wheat was to encourage pairing between grass chromosomes and wheat chromosomes. It is only through chromosome pairing that desirable genes from grass species can be transferred into durum wheat. However, a gene, called Ph1, located in chromosome 5B of wheat, does not allow pairing between the grass and wheat chromosomes. Using appropriate genetic stocks, we synthesized several hybrids without the Ph1 gene. As expected, in the absence of Ph1, pairing between chromosomes of the wheatgrasses and those of durum was enhanced more than two-fold. Using a specialized technique called fluorescent genomic in situ hybridization (Fl-GISH), we studied the specificity of chromosome pairing and confirmed wheat-grass pairing, a welcome feature from the breeding standpoint. Using this strategy of making hybrids without Ph1 should help promote "adultery" between durum and grass chromosomes and hence accelerate the transfer of desirable gene(s) into durum cultivars.
Technical Abstract: Wild grasses in the tribe Triticeae, some in the primary or secondary gene pool of wheat, are excellent reservoirs of genes for superior traits, including resistance to various diseases. Thus, the diploid wheatgrasses, Thinopyrum bessarabicum (Savul. and Rayss) Á. Löve (2n = 2x = 14; JJ genome) and Lophopyrum elongatum (Host) Á. Löve (2n = 2x = 14; EE genome), are important sources of genes for disease resistance, e.g., Fusarium head blight (FHB) resistance. These grasses are potential donors of FHB resistance to wheat. By crossing fertile amphidiploids between the two diploid species (2n = 4x = 28; JJEE) with appropriate genetic stocks of durum wheat, we synthesized trigeneric hybrids (2n = 4x = 28; ABJE) incorporating both the J and E genomes in durum background. Trigeneric hybrids with and without the homoeologous-pairing suppressor gene, Ph1, were produced. In the absence of Ph1, the chances of genetic recombination between chromosomes of the two useful grass genomes (JE) and those of the durum genomes (AB) would be enhanced. As expected, the Ph1-intergeneric hybrids showed low chromosome pairing (23.86 % of the complement), whereas the trigenerics with ph1b (49.49 %) and those with their chromosome 5B replaced by 5D (49.09 %) showed much higher pairing. Fluorescent genomic in situ hybridization (Fl-GISH) analysis afforded an excellent tool for studying the specificity of chromosome pairing: wheat with grass, wheat with wheat, or grass with grass. In the trigeneric hybrids that lacked chromosome 5B, and hence the Ph1 gene, the wheat-grass pairing was elevated, i.e., 2.6 chiasmata per cell, a welcome feature from the breeding standpoint. Using Langdon 5D(5B) disomic substitution for making trigeneric hybrids should promote "adultery" between durum and grass chromosomes and hence accelerate alien gene transfer into the durum genomes.