| Reliable and easy-to-use techniques for chromosome identification are critical in plant breeding and genome research. There are two essential tasks in chromosome identification: distinguishing chromosomes from different genomes and differentiating individual chromosomes in the complement of any given genome. The cultivated potato (Solanum tuberosum L.) is widely regarded as a difficult target for cytogenetics studies because of its small and relatively numerous chromosomes. Here I describe the development of fluorescence in situ hybridization (FISH)-based techniques for the identification of potato chromosomes, and demonstrate their utilization in potato germplasm characterization and genome research. Genomic in situ hybridization (GISH) was used to paint chromosomes from different Solanum species into distinct colors, allowing direct and unambiguous detection of alien chromosomes or chromosomal segments in potato breeding lines derived from crosses involving wild species. A set of chromosome-specific bacterial artificial chromosome (BAC) clones was isolated by screening a potato BAC library using genetically mapped restriction fragment length polymorphism (RFLP) markers as probes. The FISH signals derived from these BAC clones serve as convenient and reliable cytogenetic markers for and facilitated the identification of the specific potato chromosomes. Finally, GISH and FISH using chromosome-specific cytogenetic DNA markers were integrated into a sequential procedure, which permitted the simultaneous determination of both the genomic and chromosomal origins of a particular chromosome in potato germplasm containing chromosomes from different species. Ten putative potato - S. brevidens chromosome addition/substitution lines were analyzed by the sequential method, and seven monosomic addition lines and one monosomic substitution line were identified. The FISH-based chromosome identification system will make potato germplasm characterization a more manageable and widely used practice. |
