The 2012 ASHS Annual Conference

Rose chromosome number ranges from 14 to 56 and understanding the dynamics of rose chromosome numbers can help improve the progress made in breeding programs and enhance the understanding of certain rose populations.  A survey of the pollen size of 80 roses in a breeding collection suggested that 78% were tetraploid, 7% were triploid, and 14 % were diploid.  These results are currently being verified with flow cytometry.   Of these roses, the presence of large pollen grains indicating non reduction during meiosis occurred in 10% of the roses.  Triploid roses most commonly exhibited non reduction, but there were some diploid plants that had 2n gametes.   The triploid rose ‘Renny’ had extremely large pollen grains with many measuring greater than 50nm in diameter and a couple measuring over 70nm in diameter.  These large pollen grains were likely 3x, though these large sizes did not occur in the other suspected triploids.  A common occurrence among the triploids was the presence of irregular and shrunken pollen grains that were likely aneuploids leading to pollen abortion.   A series of interploidy crosses indicated that there were differences in set, seed yield and seed germination in crosses done between diploids or between tetraploids as compared to those done between either diploid or tetraploids and triploids.  The ploidy level of the seedlings of these crosses is being followed to determine the frequency of haploid and diploid pollen from the triploid parent that results in a viable seedling.