Genomic in situ hybridization analysis of a trigenomic hybrid involving Solanum and Lycopersicon species

A 4x potato (+) tomato fusion hybrid (2n = 4x = 48) was successfully backcr ossed with a diploid Lycopersicon pennellii (2n = 2x = 24). Genomic in situ hybridization (GISH) on somatic and meiotic chromosomes confirmed that the progenies were triploids (2n = 3x = 36) and possessed three different geno mes: potato, tomato, and L. pennellii. Therefore, they have been called tri genomic hybrids. Total genomic probes of both Lycopersicon species were fou nd to hybridize mutually, whereas the potato genome was clearly differentia ted. During metaphase I, bivalents were formed predominantly between tomato and L. pennellii chromosomes and the univalents of potato chromosomes were most common. Trivalents in all cases included homoeologous chromosomes of potato, tomato, and L. pennellii. However, the triploids were totally steri le as determined from extensive crossing. On chromosome doubling of triploi ds by shoot regeneration from callus, hexaploids (2n = 6x = 72) were obtain ed. Despite exhibiting clear allohexaploid behaviour by forming 36 bivalent s at meiosis, these were also completely sterile like their triploid counte rparts. In spite of this drawback, the prospects of chromosome pairing betw een potato L. pennellii and Solanum genomes does open the possibilities for bringing the two genera close.