And I know I don't understand the terminology or I wouldn't be asking the question, but I would have thought that the hybrids now would have more genetic diversity, not less. ???
"The species and early hybrids showed the highest genetic diversity, with genetic diversity progressively dropping from the cultivars in the mid-20th century to those produced in the late 20th century. As might be predicted, the tetraploid breeding lines displayed less genetic diversity than diploids. This work clearly shows that the intense artificial selection of plant hybrids recently taken up for ornamental domestication soon generates a measurable decline in genetic diversity. The genus offers a marvellous opportunity to investigate the effect of man-made hybridization and extreme artificial selection pressures during domestication on the genome and gene expression."
