Reproductive Behavior of Diploid and Allotetraploid Rhododendron L. ‘Fragrant Affinity’

Wide hybridization can lead to recombination of diverse traits and creation of unique phenotypes, but the resultant hybrids are often sterile as is the case with the intersubgeneric hybrid Rhododendron L. ‘Fragrant Affinity’. Sterility in wide hybrids can either be genic or chromosomal; the latter may be overcome by induction of polyploidy, which can restore chromosome homology and fertility. Cytologic studies of ‘Fragrant Affinity’ appear to support the presence of bridges between bivalents in metaphase I and laggard chromosomes in anaphase I. In the current study, an allotetraploid form of R. ‘Fragrant Affinity’ was developed using oryzalin (4-(dipropylamino)-3, 5-dinitro-benzenesulfonamide) as a mitotic inhibitor and chromosomal doubling agent. Genome sizes (2C) were determined using flow cytometry and found to be ≈1.6 and 3.2 pg for the diploid and allotetraploid, respectively. Pollen viability, determined by staining and germination tests, was 4% and 0%, respectively, for the diploid and 68% and 45%, respectively, for the allotetraploid. No seeds were produced when the diploid R. ‘Fragrant Affinity’ was used as a pistillate parent when pollinated with pollen from viable diploid and tetraploid parents. The allotetraploid produced viable seeds and seedlings when pollinated with pollen from either diploid or tetraploid parents, including self-pollination, demonstrating restored male and female fertility.