MAPPING GENETIC-FACTORS CONTROLLING POLLEN VIABILITY IN AN INTERSPECIFIC CROSS IN HELIANTHUS SECT HELIANTHUS

Segregation of 48 genetic markets, including one CMs restorer gene, on e morphological character gene, six isozymes and 40 RAPD loci, was sco red in a backcross progeny of an interspecific hybrid H. agrophyllusXH . annuus cv RHA274. A linkage map was generated taking into account se gregation distortions for 11 of the 48 loci in the frame of two differ ent 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 cov ering 390 cM. Approximately half of the plants of the BC1 were male fe rtile as expected for the segregation of one dominant male-fertility r estorer gene; however, these displayed a large range of variation for pollen viability. About 80% of this variation was explained by three g enomic regions located on linkage groups 1, 2 and 3. the observation o f meiotic chromosomes revealed a significant rate of mispairing (rod b ivalents and tetravalents) in tight correlation with pollen viability, indicating that chromosome rearrangements (translocations) are the pr eponderant factors reducing pollen viability in this progeny. Cytogene tic and mapping data suggest that the three genomic regions involved i n pollen-viability variation are located close to translocation points which differentiate the parental-species karyotypes. Segregation dist ortion was observed for loci correlated with pollen-viability variatio n. These were most likely the result of two possible suggested mechani sms.