Comparison of FDR and SDR derived tetraploid progeny from 2x x 4x crosses using haploids of Solanum tuberosum L that produce mixed modes of 2n eggs

The relationship between heterozygosity and heterosis in tetraploid potato (Solanum tuberosum subsp. tuberosum L., 2n = 4x = 48) was examined in a ser ies of first-division restitution (FDR)- and second-division restitution (S DR)-derived tetraploid subpopulations. The subpopulations were constructed using two 2n egg-producing, mixed-mode haploids (2n = 2x = 24) crossed to t hree tetraploid (2x = 4x = 48) potato clones. Half-tetrad analysis using a codominant electrophoretic marker (Pgm-2), which is closely linked to the c entromere, discriminated between FDR- and SDR-derived 4x progeny. The FDR:S DR ratio of the 4x progeny observed was dependent upon the haploid parent u sed in the 2x x 4x cross. Field studies were conducted between 1992 and 199 6 to compare the yield and specific gravity of the two subpopulations and t heir parents from three crosses. There was no difference in the total tuber yield or specific gravity between the FDR- and SDR-subpopulations based up on family means, despite the expectation that FDR-derived progeny would tra nsmit a greater portion of the genome's heterozygosity intact than SDR-deri ved progeny. The 4x parent in each family had a higher yield than either 4x progeny subpopulation. Inbreeding, as a consequence of the haploidization process and a lack of genetic diversity, may have negated any advantage of the FDR-derived progenies over the SDR-derived progenies.