Application of GISH to characterize woody ornamental hybrids with small genomes and chromosomes

Genomic in situ hybridization (GISH) is a powerful tool in distinguishing parental genomes in plant hybrids. However, in plants with small genome GISH often failed to decorate entire chromosomes. In this study, the GISH technology was adapted for woody ornamentals, commonly characterized by small genomes (between 842.8 and 2430.4 Mbp/1C or 0.86 and 2.48 pg/1C) and/or high amounts of small chromosomes (up to 82 chromosomes with size 1.4-4.8 mu m). The used GISH method was successful to label entire chromosomes by using an optimal probe/block ratio (> 1/80) and the best probe labelling and detection system (biotin vs. digoxigenin). GISH was performed on Buddleja and Hibiscus hybrids resulting from an interspecific breeding programme. For the first time, GISH on Buddleja x weyeriana'Sungold' (F2 of B. globosa x B. davidii) showed a chromosomal origin of the hybrid: 36 chromosomes inherited from B. davidii (2n = 2x = 76), 28 chromosomes from B. globosa (2n = 2x = 38) and 12 chromosomes were recombinant chromosomes between B. globosa and B. davidii. The detected chromosome constitution in B. x weyeriana points on 2n-gametes formation during meiosis of B. globosa. GISH analysis of F1 and F2 hybrids of B. davidiixB. x weyeriana crosses revealed that 16 (F1) and 10 (F2) chromosomes completely belong to B. davidii and all the other chromosomes were recombinant. This proved that all chromatin material of B. globosa was introgressed into the B. davidii chromosomes. GISH analysis of an F1 hybrid between Hibiscus syriacus x H. paramutabilis revealed 40 chromosomes of H. syriacus (2n = 4x = 80) and 41 chromosomes of H. paramutabilis (2n = 4x = 82). In an F2 hybrid of H. syriacus xH. paramutabilis 25 recombinant chromosomes were detected, indicating introgression of H. syriacus DNA in H. paramutabilis