A cytomolecular approach to assess the potential of gene transfer from a crop (Triticum turgidum L.) to a wild relative (Aegilops geniculata Roth.)

When a crop hybridizes with a wild relative, the potential for stable transmission to the wild of any crop gene is directly related to the frequency of crop-wild homoeologous pairing for the chromosomal region where it is located within the crop genome. Pairing pattern at metaphase I (MI) has been examined in durum wheat x Aegilops geniculata interspecific hybrids (2n=4x=ABU(g)M(g)) by means of a genomic in-situ hybridization procedure that resulted in simultaneous discrimination of A, B and wild genomes. The level of MI pairing in the hybrids varied greatly depending on the crop genotype. However, their pattern of homoeologous association was very similar, with a frequency of wheat-wild association close to 60% in all genotype combinations. A-wild represented 80-85% of wheat-wild associations which supports that, on average, A genome sequences are much more likely to be transferred to this wild relative following interspecific hybridization and backcrossing. Combination of genomic DNA probes and the ribosomal pTa71 probe has allowed to determine the MI pairing behaviour of the major NOR-bearing chromosomes in these hybrids (1B, 6B, 1U(g) and 5U(g)), in addition to wheat chromosome 4A which could be identified with the sole use of genomic probes. The MI pairing pattern of the wild chromosome arms individually examined has confirmed a higher chance of gene escape from the wheat A genome. However, a wide variation regarding the amount of wheat-wild MI pairing among the specific wheat chromosome regions under analysis suggests that the study should be extended to other homoeologous groups.