Genetic and ecological aspects of gene flow from wheat (Triticum aestivum L.) to Aegilops L. species

Genetic and ecological aspects of gene flow from wheat (Triticum aestivum L.) to Aegilops L. species Hybridisation and introgression from crops to wild relatives is a key issue in risk assessment. In the present study, hybridisation and introgression dynamics from hexaploid wheat (2n=42) to tetraploid Aegilops species (2n=28) were investigated by experiments in natural conditions or in the greenhouse, and by genetic analyses. In order to study crop-weed hybridisation as a function of distance, a field trial was set up where Ae. cylindrica was planted in plots at 0, 1, 5, 10 and 25m from a wheat field. In the progeny (14045 seeds sown) we detected hybrids up to 1m from the wheat field. Wheat-specific RAPD fragments were found in Ae. cylindrica x T. aestivum hybrids and BC1 plants. Using a set of Chinese Spring nulli-tetrasomic wheat lines, we were able to assign DNA fragments to wheat chromosomes. Introgressed wheat-specific markers were localised on the three genomes (A, B and D). Some of these markers were transformed into easy-to-use Sequence Characterised Amplified Regions (SCARs), and used to characterise an introgressive series. Ae. cylindrica x GM-wheat hybrids, BC1 and BC1S1 (self-fertilised first backcrosses) were manually produced, in order to study inheritance of transgenes. Female fertility of the hybrids was 0.03-0.6%, BC1 plants had 30-84 chromosomes and displayed highly irregular meioses, their self fertility ranged from 0 to 5.21 %. BC1S1 plants had 28-43 chromosomes and some of them recovered full fertility. One BC1S1 individual contained the bar gene issued from its transgenic wheat progenitor and survived herbicide treatment. A RAPD-based population genetics study was carried out in natural Ae. cylindrica populations, most of them from adventive locations in Switzerland, Italy and the USA. Genetic diversity was low and most of the variance resided among populations. Italian populations from the Aosta valley and a Swiss population were similar or identical to northern American populations indicating that the species may have crossed the Atlantic Ocean several times. Using 52 Ae. geniculata individuals planted in a winter wheat field, we obtained an overall Ae. geniculata x T. aestivum hybridisation rate of 0.94%, hybrid fertility, i.e. BC1 production rate, was 2.2%. Specific wheat SCAR markers were detected in the hybrids and backcrosses. Gene flow is thus possible between wheat and Aegilops, at a limited rate. Because of the large cultivation of wheat, trans-gene flow might occur significantly. Moreover, insertion of the transgene on A and B genome does not prevent introgression.

Thèse de doctorat : Université de Neuchâtel, 2005 ; 1872