Effect of transgene genome location on the risk of gene migration from herbicide resistant wheat (Triticum aestivum L.) to jointed goatgrass (Aegilops cylindrica Host.)

The ability of jointed goatgrass to hybridize with wheat raises questions concerning the gene migration of herbicide resistance gene from wheat to the jointed goatgrass. A potential avenue for minimizing gene migration is to place the resistance gene on the A or B genome of wheat. Crosses were made between wheat genotypes carrying the resistance gene on the A-, B- or D-genome and jointed goatgrass to produce hybrids. Hybrids were subsequently backcrossed to jointed goatgrass to produce the BC1 and BC 2 generations. Additionally, BC2S1 and BC 2S2 generations were produced. Backcross generations were assayed for chromosome number, gene transmission rates, and germination rates. The BC1 generation was divided into two sub-populations, one sprayed with glyphosate and the other not sprayed. Gene retention in the sprayed and non-sprayed sub-populations was higher than expected for the A-genome in both sub-populations and in the D-genome for the sprayed sub-population. It was concluded that higher gene transmission in the BC1 was occurring due to meiotic chromosome restitution and/or chromosome non-disjunction. Gene retention and germination rates were different between the two BC2 generations derived from sprayed and non-sprayed BC1 plants. The BC2 generation derived from sprayed BC, plants had lower germination and a higher than expected gene transmission rate for all three genomes. In contrast, the BC2 generation derived from positive non-sprayed BC1 plants had the expected gene transmission rate of 50%. Gene transmission rates were higher than the expected 25% in the BC2 non-sprayed derived from both positive and negative non-sprayed BC1 plants. It was concluded that residual glyphosate in the sprayed BC1 plants was causing gametophytic and/or sporophytic selection for gametes or seeds carrying the glyphosate resistance gene. BC2S1 and BC2S 2 generations were evaluated for the retention of wheat chromatin specific to chromosome 4B by using molecular markers. Whole chromosomes and chromosomal segments specific to chromosome 4B were retained in the BC2S 1 and BC2S2 generations indicating translocations involving the 4B chromosome had occurred. Based on these results, it was concluded that placement of herbicide resistance gene on the unshared genomes of wheat will not significantly limit gene migration from wheat to jointed goatgrass.