MITOTIC AND MEIOTIC IRREGULARITIES IN SOMATIC HYBRIDS OF LYCOPERSICON-ESCULENTUM AND SOLANUM-TUBEROSUM

Chromosome numbers were determined in metaphase complements of root-ti p meristems of 107 tomato (+) potato somatic hybrids, obtained from fi ve different combinations of parental genotypes. Of these hybrids 79% were aneuploid, lacking one or two chromosomes in most cases. All four hybrids that were studied at mitotic anaphase of root tips showed lag gards and bridges, the three aneuploids in a higher frequency than the single euploid. Hybrid K2H2-1C, which showed the highest percentage o f aberrant anaphases, possessed 46 chromosomes. Fluorescence in situ h ybridization with total genomic DNA showed that this hybrid contained 23 tomato, 22 potato, and 1 recombinant chromosome consisting of a tom ato chromosome arm and a potato chromosome arm. The potato parent of K 2H2-1C was aneusomatic in its root tips with a high frequency of monos omic and trisomic cells and a relatively high frequency of cells with one fragment or telosome. Meiotic analyses of three tomato (+) potato somatic hybrids revealed laggards, which occurred most frequently in t he triploid hybrids, and bridges, which were frequently present in pol len mother cells (PMCs) at anaphase I of hypotetraploid K2H2-1C. We ob served putative trivalents in PMCs at diakinesis and metaphase I of eu triploid A7-82A and quadrivalents in part of the PMCs of hypotetraploi d K2H2-1C, suggesting that homoeologous recombination between tomato a nd potato chromosomes occurred in these hybrids. All three hybrids sho wed a high percentage of first division restitution, giving rise to un reduced gametes. However, shortly after the tetrad stage all microspor es completely degenerated, resulting in exclusively sterile pollen.