GENOMIC IN-SITU HYBRIDIZATION (GISH) AND RFLP ANALYSIS FOR THE IDENTIFICATION OF ALIEN CHROMOSOMES IN THE BACKCROSS PROGENY OF POTATO(+)TOMATO FUSION HYBRIDS

Backcross progenies, BC1 and BC2, derived from crossing a hexaploid po tato (+) tomato fusion hybrid to tetraploid potato, were monitored for the presence of alien tomato chromosomes. For discriminating the toma to chromosomes from those of potato, both mitotic and meiotic chromoso me preparations were labelled differentially through total genomic DNA in situ hybridization (GISH). The presence or absence of individual t omato chromosomes in the BC progeny was identified through RFLP analys es using chromosome-specific DNA probes. The results indicated that th e BC1 plant possessed only nine chromosomes of tomato instead of the e xpected haploid set of 12. Of the nine persistent tomato chromosomes, there were three pairs that formed bivalents and three singles that fo rmed univalents at meiosis. One of the single chromosomes was striking ly longer as a result of some structural mutation and could easily be identified in the hexaploid parent, the BC1 and in some of the BC2 pla nts. From the analyses of BC2 progeny there were indications of the pr esence in the BC1 of tomato chromosomes 1, 3 and 6 in duplicate, and c hromosomes 8, 9 and 10 in the haploid condition. The number of tomato chromosomes transmitted to BC2 plants varied from one to six. The resu lts of GISH revealed that a few BC2 plants possessed more tomato chrom osomes than those deduced from RFLP analysis. This indicated the prese nce of some tomato chromosomes in duplicate and others in the haploid condition. The potential value of these genotypes for establishing pot ato lines with additions and substitutions of tomato chromosomes is di scussed.