The Utilization of the Polyploid Nature of Roses
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2015, International Society for Horticultural Science. All rights reserved. Rose chromosome number ranges from 14 to 56. The understanding of 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 110 roses in the TAMU breeding collection suggested that 61% were tetraploid, 34.5% were diploid, and 3.6% were hexaploid. Of these roses, the presence of large pollen grains indicating non reduction during meiosis occurred in 20% of the diploids, and 4% of the tetraploids. Triploid roses commonly exhibited non reduction as well as the presence of irregular and shrunken pollen grains that were likely aneuploids leading to pollen abortion. The results were compared with chromosome counts to determine the accuracy of using pollen size as a ploidy indicator. Pollen size alone was 80% successful at identifying diploids and 84% successful at identifying tetraploids. When pollen appearance was combined with the pollen size, 58% of the triploids were identified. A few of the diploid and tetraploid individuals were falsely grouped as triploids. 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 was followed to determine the frequency of haploid and diploid pollen from the triploid parent that resulted in a viable seedling. In crosses with a tetraploid female parent and a triploid pollen parent, 55% of the progeny were triploid, 41% of the progeny were tetraploid, and 3% were pentaploid. In crosses with a diploid female and a triploid male, 20% of the progeny were diploid, 75% were triploid and 4% were tetraploid.
