The role of cytogenetic tools in orchid breeding

Orchidaceae species account for one-tenth of all angiosperms including more than 30,000 species having significant ecological, evolutionary, and economic importance. Despite Orchidaceae being one of the largest families among flowering plants, crucial cytogenetic information for studying species diversification, inferring phylogenetic relationships, and designing efficient breeding strategies is lacking, except for 10% or less of orchid species cases involving mostly chromosome number or karyotype analysis. Also, only approximately 1.5% of the identified orchid species from less than a hundred genera have genome size data that provide crucial information for breeders and molecular geneticists. Various molecular cytogenetic techniques, such as fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH), have been developed for determining ploidy levels, analyzing karyotypes, and evaluating hybridity, in several ornamental crops including orchids. The estimation of genome size and the determination of nuclear DNA content using flow cytometry have also been employed in some Orchidaceae subfamilies. These different techniques have played an important role in supplementing beneficial knowledge for effective plant breeding programs and other related plant research. This review focused on orchid breeding summarizes the status of current cytogenetic tools in terms of background, advancements, different techniques, significant findings, and research challenges. Principal roles and applications of cytogenetics in orchid breeding as well as different ploidy level determination methods crucial for breeding are also discussed.