The extent and position of homoeologous recombination in a distant hybrid of Alstroemeria: a molecular cytogenetic assessment of first generation backcross progenies

To estimate the extent and position of homoeologous recombination during me iosis in an interspecific hybrid between two distantly related Alstroemeria species, the chromosome constitution of six first generation backcross (BC 1) plants was analysed using sequential fluorescent in situ hybridization ( FISH) and genomic in situ hybridization (GISH) analysis. Four different pro bes were used for the FISH analysis: two species-specific and two rDNA prob es. The six BC1 plants were obtained from crosses between the hybrid A. aur ea x A. inodora with its parent A. inodora. GISH clearly identified all chr omosomes of both parental genomes as well as recombinant chromosomes. The s equential GISH and FISH analysis enabled the accurate identification of all individual chromosomes in the BC1 plants, resulting in the construction of detailed karyotypes of the plants. The identification of the recombinant c hromosomes provided evidence which chromosomes of the two species are homoe ologous. Two of the BC1 plants were aneuploid (2n=2x+1=17) and four triploi d (2n=3x=24), indicating that both n and 2n gametes were functional in the Fl hybrid. Using GISH, it was possible to estimate homeologous recombinatio n in two different types of gametes in the F-1 hyrid. The positions of the crossover points ranged from highly proximal to distal and the maximum numb er of crossover points per chromosome arm was three. Compared with the aneu ploid plants, the triploid plants (which received 2n gametes) clearly posse ssed fewer crossovers per chromosome, indicating reduced chromosome pairing /recombination prior to the formation of the 2n gametes. Besides homeologou s recombination, evidence was found for the presence of structural rearrang ements (inversion and translocation) between the chromosomes of the parenta l species. The presence of the ancient translocation was confirmed through FISH analysis of mitotic and meiotic chromosomes.