FISH chromosome mapping allowing karyotype analysis in Medicago truncatula lines Jemalong J5 and R-108-1

Two lines of Medicago truncatula, R-108-1 and Jemalong J5, exhibit differences in their symbiotic properties, morphological markers, and capacity for regeneration and transformation. Using cytogenetic techniques, we detected differences in chromomycin A(3) straining on the two sides of the secondary constriction of the nucleolar chromosome pair of J5 and R-108-1, while DAPI (4', 6-diamidino-2-phenylindole) staining revealed no differences between the two lines. FISH (fluorescent in situ hybridization) analysis showed a difference between J5 and R-108-1 for the same 5S rRNA genes; three loci were found in J5 but only two loci in R-108-1. However, for the 18S-5.8S-26S rDNA genes only a single locus was found in both lines. Based on these analyses, a karyotype for the two lines was established.