Introgression of Lilium rubellum Baker chromosomes into L-longiflorum Thunb.: A genome painting study of the F-1 hybrid, BC1 and BC2 progenies

Interspecific hybrids between Lilium longiflorum (L, 2n = 2x = 24) and Lili um rubellum (R, 2n = 2x = 24) were produced with the aim of transferring de sirable horticultural traits from L. rubellum to L. longiflorum. All F-1 hy brids (LR, 2n = 2x = 24) and BC1 individuals (LLR, 2n = 3x = 36) were pheno typically uniform for plant height, flowering time, leaf shape and flower c olour. The BC1 plants were, in spite of their triploid nature, fertile and could be used as a female parent in backcrossings with autotetraploid L. lo ngiflorum (LLLL, 2n = 4x = 48). Twelve BC2 individuals were obtained and th ree of them were selected for further chromosome analysis. As L. longifloru m and L. rubellum chromosomes were indistinguishable in the hybrids, genomi c in- situ hybridization (GISH) was applied to establish the parentage of t he chromosomes of the F-1 hybrids and the BC1 and BC2 progenies. GISH confi rmed the LLRR constitution of the doubled amphimonoploid (allodiploid), and the LLR constitution of all BC1 plants. The three selected BC2 plants were , as expected, aneuploid, containing three complete sets of L. longiflorum chromosomes and six, seven or eight L. rubellum chromosomes, respectively. However, L/R translocation or recombinant chromosomes could not be demonstr ated in the mitotic metaphase complements of the F-1, BC1 and BC2 plants. I n spite of the high frequencies of homoeologous recombination in the F-1 hy brids (LR) pollen was found to be sterile in all cases. At metaphase I of t he pollen mother cells of the BC1 plants, genome painting did not reveal an y cases of homoeologous pairing and recombination between L and R chromosom es. This lack of exchange between homoeologous chromosome segments indicate s complete preferential pairing of the L and R chromosomes in the F-1 (amph idiploid) and BC1 plants. It seems that the preferential pairing in the F-1 and BC1 hybrids hinder the introgression of the chromosome segments or spe cies-specific genes into the recipient for breeding purposes.