Genome discrimination in progeny of interspecific hybrids between Brassica napus and Raphanus raphanistrum

Abstract

Genomic in situ hybridization (GISH) applied to the F1 interspecific hybrid between oilseed rape (Brassica napus, AACC, 2n = 38) and wild radish (Raphanus raphanistrum, RrRr, 2n = 18) showed the predicted 19 chromosomes from B. napus and 9 chromosomes from R. raphanistrum. The very low female fertility of these interspecific hybrids when backcrossed to R. raphanistrum led to only two descendants. Their chromosome number varied between 45 and 48. Both of these progenies showed only 9 chromosomes from R. raphanistrum and 36-39 chromosomes from B. napus. These results indicate the efficiency and limits of GISH as a suitable tool to assess and interpret the behavior of chromosomes after such interspecific crosses. The unexpected chromosome combination is discussed.

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

“…When B. napus served as the female parent, the hybrids were mainly triploid (ACRr, 2n = 28 chromosomes) and produced few seeds (Chèvre et al 1998;Darmency et al 1998). When backcrossed to R. raphanistrum, the hybrids produced only two progeny; both of which showed nine R. raphanistrum chromosomes and 36-39 chromosomes from B. napus (Benabdelmouna et al 2003). In field experiments, B. napus × R. raphanistrum hybrids have reduced fitness, with delayed and lower seedling emergence, lower survival, and reduced rosette diameter and dry matter than either parent (Chadoeuf et al 1998;Guéritaine et al 2003a).…”

Lack of stable inheritance of introgressed transgene from oilseed rape in wild radish

“…One possible explanation for the apparently normal chromosome number is loss of wild radish chromosomes (e.g. 2n = 17+1) as was previously discussed in the case of the BC1 generation (Benabdelmouna et al, 2003). This could in turn explain high disturbance in chromosome behavior and high chromosome number variability.…”

“…Many chromosomal anomalies have been previously demonstrated in Brassica hybrids (Baranger et al, 1995;Benabdelmouna et al, 2003;Chèvre et al, 1998Chèvre et al, , 1999Guéritaine et al, 2002). Introgressed chromosomes are very unstable in the absence of a homologous chromosome with which to pair at meiosis.…”

“…However, the prospect of stable introgression of herbicide resistance to wild radish in nature seems remote. Where selection is not present or occurs infrequently, cytogenetic disorders resulting in weak growth, low fitness under competition in the field (Benabdelmouna et al, 2003;Guéritaine et al, 2002, Table 2. Chromosome counts in wild populations of wild radish and glufosinate-resistant and susceptible plants of generation G9.…”

“…Although only four such hybrids have been reported with wild radish as the female parent (Chèvre et al, 2000;Darmency et al, 1998;Warwick et al, 2003), more can be generated through reciprocal crosses (Baranger et al, 1995;Chèvre et al, 2000;Darmency et al, 1998;Eber et al, 1994;Rieger et al, 2001). Hybrids were very infertile but produced a few progeny with restored fertility (Benabdelmouna et al, 2003;Chèvre et al, 1997aChèvre et al, , 1998Chèvre et al, , 1999Darmency et al, 1998;Guéritaine et al, 2003). However, whether the enhanced fitness value conferred by the transgene could alter the behavior of the wild species depends on the likelihood of stable genomic introgression.…”