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

Author
item Mcgrath, J Mitchell - Mitch
item Helgeson, John

Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: We have been obtaining new disease resistances to viruses, bacteria and fungi by somatic hybridization of potato with wild, sexually incompatible species related to potato. The wild species are often very resistant to the diseases but plant breeders have not been able to use the genes for these resistances because crossing of the wild species with potato is not possible. Thus we have fused leaf cells of the wild species and potato. The resulting product is placed on a nutrient medium which induces it to form a new plant. In the present study we have used a new microscope technique to look at what happens to the chromosomes of the two species when they are combined. The DNA of the 2 species was stained with different dyes which show different colors under ultra violet light. Using this technique we see that the DNA of the two species does not seem to be dividing in complete synchrony. This may affect the degree to which the recombination of the DNA of the two species occurs in breeding studies. However, it is clear that some mixing of the DNA of the species does occur giving some assurance that the traits for the wild plants can be incorporated into improved potato lines. If this is so, the new resistances that we can bring into potato may lead to new defense against the diseases which cost American producers more than $200 million each year in pesticides and loss from disease.

Technical Abstract: Fluorescent in situ hybridization was used to characterize loci encodingribosomal RNA (rDNA) among parents and progeny of a somatic fusion between tetraploid Solanum tuberosum (potato) and diploid S. brevidens. As expected, four major sites of hybridization to rDNA loci were evident in the tetraploid parent species, two in the diploid parent species and six in the hexaploid somatic fusion plant. Unexpectedly, two of the loci in the somatic fusion plant showed later condensation relative to the other four. This delayed condensation was heritable to the first backcross generation of the somatic hybrid crossed with potato. In the second backcross generation, differential condensation was not evident. However, a heterochromatic isochromosome was observed whose presence was correlated with an S. brevidens-specific marker linked with the rDNA locus. It is suggested that the S. brevidens rDNA loci are preferentially affected in the somatic hybrid and its progeny. Further, the observed delayed condensation of S. brevidens rDNA loci may have contributed to the formation of the isochromosome.