Genomic characterisation and the detection of raspberry chromatin in polyploid Rubus

This paper reports genomic in situ hybridization (GISH) and fluorescent ins itu hybridization (FISH) data for chromosomes of raspberry (Rubus idaeus 2n = 2x = 14), blackberry (Rubus aggregate, subgenus Eubatus. 2n = 2-12x = 14 -84) and their allopolyploid derivatives used in fruit breeding programmes. GISH was used to discriminate labelled chromosomes of raspberry origin fro m those of blackberry origin in allopolyploid hybrid plants. The raspberry chromosomes were labelled by GISH at their centromeres, and 1 chromosome wa s also labelled over the short arm. In one allopentaploid plant a chromosom e carried a terminal signal. Karyotype analysis indicated that this is a bl ackberry chromosome carrying a raspberry translocation. GISH analysis of an aneuoctaploid blackberry cv 'Aurora' (2n = 8x = 58) showed that both whole and translocated raspberry chromosomes were present. The basic Rubus genom e has one ribosomal DNA (rDNA) locus, and in all but one case all levels of ploidy had the expected multiples of rDNA loci. Interestingly, in the blac kberry cv 'Aurora', there were only six sites, two less than might be predi cted from its aneuoctaploid chromosome number. Our results highlight the po tential of GISH and FISH for genomic designation, physical mapping and intr ogression studies in Rosaceous fruit crops.