Transmission of alien tomato chromosomes from BC1 to BC2 progenies derived from backcrossing potato (+) tomato fusion hybrids to potato: the selection of single additions for seven different tomato chromosomes

 By backcrossing three BC₁ genotypes of potato (+) tomato fusion hybrids to different tetraploid potato pollinators, BC₂ populations were produced. A combined total of 97 BC₂ plants from three BC₂ populations were analysed with chromosome-specific probes through restriction fragment length polymorphism (RFLP) for the presence of alien tomato chromosomes. The number of different alien tomato chromosomes transmitted through the female BC₁ parent ranged from 0 to 6, and the average number of different alien chromosomes transmitted per BC₂ plant varied between 1.7 and 3.4 in the different populations. This variation corresponded to the chromosome constitution of the individual BC₁ parents: parent 6739, which possessed 11 different alien chromosomes in a single condition, gave rise to progeny with a lower average number of alien chromosomes per plant than the BC₁ parent 2003 that possessed 2 of the 12 alien chromosomes in a disomic condition. In the latter case, the higher transmission rate was attributed to the more regular distribution of the two alien chromosomes in the disomic condition because of regular bivalent formation during meiosis as revealed by genomic in situ hybridisation (GISH) and fluorescent in situ hybridisation (FISH). The transmission frequencies of individual alien chromosomes were subjected to statistical analysis to test whether the maternal genotypes had an effect on alien-chromosome transmission. Among the BC₂ plants, a total of 27 single additions were detected for as many as seven different chromosomes (1, 2, 4, 6, 8, 10 and 12) out of the 12 possible types. Received: 4 March 1997 / Accepted: 28 August 1997