Cytogenetic approaches enhance advanced breeding in woody ornamental species

Molecular cytogenetic techniques are valuable tools to study chromosome structure and genome constitution and to perform gene mapping and visualization of chromosomal recombination. In woody ornamental species, which are often characterized by small genomes, small-sized chromosomes and low mitotic index in the tiny-to-handle roots, cytogenetic studies are hardly exploited. We developed the “SteamDrop” protocol, which enabled us to prepare high quality chromosome slides for several woody genera e.g. Buxus, Hydrangea, Buddleja, Hibiscus and Rosa. Study of chromosome number and chromosome morphology, together with knowledge of genetic relationships between species, allowed us to create more straightforward breeding programs for these genera. We also successfully implemented genomic in situ hybridisation (GISH) in different woody ornamental species to prove the hybrid nature of offspring from interspecific crosses within Buddleja and Hibiscus. In addition, knowledge of the physical position of specific genes on chromosomes might promote more efficient breeding and selection. We optimised FISH and Tyramide-FISH on mitotic and pachytene chromosomes of roses. Several single-copy genes (1.1-3 kb) involved in abiotic and biotic stress resistance mechanisms were physically mapped on Rosa wichurana Crep. chromosomes 1, 4 and 7 and genetically mapped on the genetic linkage groups. By this, an anchoring of genetic and physical maps was achieved. In the future, these results will facilitate to pyramid stress related genes in specific genotypes.