Prospects for introgressing tomato chromosomes into the potato genome: An assessment through GISH analysis

With a view to assess the possibility of homoeologous pairing and crossing- over between the chromosomes of potato (Solanum tuberosum) and tomato (Lyco persicon esculentum), a somatic fusion hybrid and two monosomic alien tomat o addition genotypes were investigated through genomic in situ hybridisatio n (GISH). The somatic fusion hybrid, C31-17-51, was near hexaploid (2n = 6x - 4 = 68) possessing 46 potato chromosomes + 20 tomato chromosomes + trans located chromosomes. The two alien addition genotypes were near tetraploids (2n = 4x + 1 = 49) and consisted of monosomic alien additions for tomato c hromosome 1 in genotype 2103-1, and tomato chromosome 8 in genotype 2301-2. In the fusion hybrid the tomato pachytene chromosome identification reveal ed that the chromosomes 1, 2, 5, 6, 7, 10, and 12 were in diploid condition whereas among those that were in haploid condition, three could be identif ied viz., 4, 9, and 11. The remaining three chromosomes could not be cytolo gically identified. Although the chromosomes with translocated segments cou ld not be identified at the pachytene stage due to technical difficulties, there was clear evidence for the presence of a reciprocal translocation obs erved at diakinesis and metaphase I stages. Because of autosyndetic pairing of the translocated segments, it gave a false impression as if there was a high frequency (86.0%) of allosyndetic pairing. In contrast to the fusion hybrid, the two alien monosomic addition genotypes showed a very low freque ncy of allosyndetic pairing, namely 1.1 and 1.3% respectively for the monos omic additions 1 and 8. In the genotype 2301-2, monosomic addition for toma to chromosome 8, crossing-over between the homoeologous chromosomes was est imated to occur in 0.8% of the meiotic cells investigated. Despite this low frequency of homoeologous pairing and crossing-over, there is a possibilit y for introgressing tomato chromosomal DNA into the potato genome through i ntergenomic recombination.