Rhododendron 'Grand Slam', which is a Harold Greer hybrid documented as 'Trude Webster' x 'Lydia', has been determined to be a tetraploid using flow cytometry by
Dr. João Loureiro, Dr. Silvia Castro, José Cerca, and Mariana Castro
Plant Ecology and Evolution Group,
Centre for Functional Ecology,
Department of Life Sciences,
Faculty of Science and Technology,
University of Coimbra, Portugal.
Rhododendron 'Grand Slam' has as ancestors 'Broughtonii', 'Pink Pearl', 'Cynthia', 'Countess of Derby', 'Trude Webster', 'Antoon van Welie', and 'Lydia'.
Both of the parents of 'Grand Slam' have 'Pink Pearl' as an ancestor.
In the case of the tetraploid 'Grand Slam', a tetraploid crossed with a triploid produced a tetraploid indicating that reduced meiosis most likely occurred for both parents. In other words, 'Grand Slam' having 52 chromosomes received something similar to 26 chromosomes each from both the tetraploid 'Trude Webster' and the triploid 'Lydia'.
Rhododendron 'Grand Slam' was also determined to be a tetraploid using flow cytometry by Dr. Thomas Ranney, J.R. Jones, and Nathan Lynch.
Summary of Ploidy Levels
Triploid 'Broughtonii',
Triploid 'Cynthia',
Triploid 'Lydia',
Triploid 'Pink Pearl',
Tetraploid 'Antoon van Welie',
Tetraploid 'Countess of Derby',
Tetraploid 'Grand Slam',
Tetraploid 'Trude Webster'
Source: Greer Gardens
John and Sally Perkins
