Molecular cytogenetics in hop (Humulus lupulus L.) and identification of sex chromosomes by DAPI-banding

Hop ( Humulus lupulus L.) was karyotyped by Fluorescence In Situ Hybridization ( FISH) with probes 18S-25S and 5S rDNA as well as DAPI banding and measurements of lengths of chromosome. Irrespective of the sex of the plants these probes revealed one signal near the telomere of chromosome 6 and two signals each on chromosomes 2 and 5. The shortest chromosome in a metaphase plate of a male plant was designated to be chromosome Y. It displayed neither signals with FISH nor DAPI bands. A middle sized metacentric chromosome with no telomeric but with an interstitial DAPI band on the short arm was designated as X. All autosomes displayed telomeric DAPI-positive bands. For the first time all mitotic hop chromosomes including the sex chromosomes were identified by methods of molecular cytogenetics.