DIFFERENTIAL BEHAVIOR OF SOLANUM BREVIDENS RIBOSOMAL DNA LOCI IN A SOMATIC HYBRID AND ITS PROGENY WITH POTATO

Fluorescence in situ hybridization was used to characterize loci encod ing ribosomal RNA (rDNA) among parents and progeny of a somatic fusion between tetraploid Solanum tuberosum (potato) and diploid Solanum bre videns. As expected, four major sites of hybridization to rDNA loci we re evident in the tetraploid parent species, two in the diploid parent species, and six in the hexaploid somatic fusion plant. Two of the lo ci in the somatic fusion plant showed differential signals relative to the other four, which were interpreted as a delayed condensation of s ites harboring the rDNA loci. This delayed condensation was heritable to the first backcross generation of the somatic hybrid crossed with p otato. In the second backcross generation, differential condensation w as not evident. However, a heterochromatic isochromosome was observed whose presence was correlated with a S. brevidens specific marker link ed with the rDNA locus. It is suggested that the S. brevidens rDNA loc i are preferentially affected in the somatic hybrid and its progeny, a nd that the delayed condensation may have contributed to the formation of the isochromosome.