TRANSMISSION OF ALIEN TOMATO CHROMOSOMES FROM BC1 TO BC2 PROGENIES DERIVED FROM BACKCROSSING POTATO(- THE SELECTION OF SINGLE ADDITIONS FOR7 DIFFERENT TOMATO CHROMOSOMES() TOMATO FUSION HYBRIDS TO POTATO )

By backcrossing three BC1 genotypes of potato (+) tomato fusion hybrid s to different tetraploid potato pollinators, BC2 populations were pro duced. A combined total of 97 BC2 plants from three BC2 populations we re analysed with chromosome-specific probes through restriction fragme nt length polymorphism (RFLP) for the presence of alien tomato chromos omes. The number of different alien tomato chromosomes transmitted thr ough the female BC1 parent ranged from 0 to 6, and the average number of different alien chromosomes transmitted per BC2 plant varied betwee n 1.7 and 3.4 in the different populations. This variation corresponde d to the chromosome constitution of the individual BC1 parents: parent 6739, which possessed 11 different alien chromosomes in a single cond ition, gave rise to progeny with a lower average number of alien chrom osomes per plant than the BC1 parent 2003 that possessed 2 of the 12 a lien chromosomes in a disomic condition. In the latter case, the highe r 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 hybr idisation (GISH) and fluorescent in situ hybridisation (FISH). The tra nsmission frequencies of individual alien chromosomes were subjected t o statistical analysis to test whether the maternal genotypes had an e ffect on alien-chromosome transmission. Among the BC2 plants, a total of 27 single additions were detected for as many as seven different ch romosomes (1, 2, 4, 6, 8, 10 and 12) out of the 12 possible types.