Mapping genetic factors controlling pollen viability in an interspecific cross in Helianthus sect. Helianthus.

Segregation of 48 genetic markers, including one CMS restorer gene, one morphological character gene, six isozymes and 40 RAPD loci, was scored in a backcross progeny of an interspecific hybrid H. argophyllusxH. annuus cv RHA274. A linkage map was generated taking into account segregation distortions for 11 of the 48 loci in the frame of two different models considering locus-pair segregation in the context of either independent selection pressures or non-equilibrated parental classes. The map consists of nine linkage groups and nine isolated markers covering 390 cM. Approximately half of the plants of the BC1 were male fertile as expected for the segregation of one dominant male-fertility restorer gene; however, these displayed a large range of variation for pollen viability. About 80% of this variation was explained by three genomic regions located on linkage groups 1, 2 and 3. The observation of meiotic chromosomes revealed a significant rate of mispairing (rod bivalents and tetravalents) in tight correlation with pollen viability, indicating that chromosome rearrangements (translocations) are the preponderant factors reducing pollen viability in this progeny. Cytogenetic and mapping data suggest that the three genomic regions involved in pollen-viability variation are located close to translocation points which differentiate the parental-species karyotypes. Segregation distortion was observed for loci correlated with pollen-viability variation. These were most likely the result of two possible suggested mechanisms.