MECHANISMS OF 2N POTATO POLLEN FORMATION IN DIHAPLOID SOLANUM-TUBEROSUM L X S-CHACOENSE BITT HYBRID CLONES

The backcrosses of dihaploid Solanum tuberosum with wild species hybri ds generating tetraploids progenies require the formation of non-reduc ed pollen. In this work, the mechanisms responsible for the formation of 2n pollen in 28 dihaploid Solanum tuberosum x Solanum chacoense hyb rids were studied. Four mechanisms were found: parallel spindles (ps), fused spindles (fs), premature cytokinesis-1 (pc-1) and premature cyt okinesis-2 (pc-2). The ps mechanism was the most frequent, being found in 23 of the 28 assessed clones. The ps and fs mechanisms led to the formation of dyads by first division restitution (FDR), transferring a bout 80% of the heterozygosity to the progenies. The pc-1 and pc-2 mec hanisms also led to the formation of dyads, but they were genetically equivalent to second division restitution (SDR), transferring only 40% of the heterozygosity to the progenies. Occurrence of FDR and SDR wer e shown to be associated in 12 clones, indicating that the clones can produce non-reduced microspores by more than one mechanism. However, o nly one mechanism is functional in a single pollen-grain mother-cell. Clones 9-2, 9-3, 9-6 and 15-15 are recommended for use in 4x x 2x mati ngs.