Rhododendron 'Rwain', which is a Marc Colombel hybrid documented as 'Kerneostic' X 'Lem's Monarch', has been determined to be a triploid 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.
The University of Coimbra research team also determined the Colombel cross of 'Horizon Monarch' by 'Rwain' produced a triploid and 3 tetraploids, 'Hotei' x 'Rwain' produced a triploid, the Colombel cross of 'Rwain' X 'L'Engin' produced 4 tetraploids, and the Colombel cross of 'Naselle' X 'Rwain' produced a diploid.
Thus, 'Rwain' is a seed and pollen fertile triplod capable of producing offspring that are diploids, triploids, and tetraploids. Although 'Rwain' is fertile, crosses involving 'Rwain' normally produce very few viable seeds.
These findings suggest that for the genus Rhododendrons triploids may provide a path for the exchange of generic material between diploids and tetraploids. To date the evidence suggesting a flow from diploid to tetraploid is much stronger than the evidence for a path from tetraploid to diploid.
Uneven bell curve splitting of fertile triploids allowing triploids to act as a donor of 1x or 2x gametes is demonstrated to occur in the research done in the thirties by Dr. Cyril Dean Darlington and in the nineties by Dr. Justin Ramsey.
These findings are consistent with the observations that Jim Barlup and Marc Colombel made when working with suspected polyploid elepidotes and the rules of engagement of John and Sally Perkins when working with deciduous azaleas.
'Lem's Monarch' and 'Horizon Monarch' have been determined to be tetraploids using flow cytometry by Dr. Thomas Ranney, J.R. Jones, and Nathan Lynch.
"Chromosomes and Plant Breeding", Macmillan (1932).
"Neopolyploidy in Flowering Plants" (2002).
"Let’s talk hybridizing: Hybridizing with elepidote polyploid rhododendrons." (2002)
"Rules of Engagement" (2009)
"Ploidy Levels and Relative Genome Sizes of Diverse Species, Hybrids, and Cultivars of Rhododendron" (2006)
Summary of Ploidy levels
Diploid 'Anna',
Diplid 'Countess of Athlone',
Diploid 'Hotei',
Diploid 'Naselle',
Diploid 'Norman Gill' ,
Diploid 'The Honourable Jean Marie de Montague',
Diploid 1 seedling of 'Naselle' X 'Rwain',
Triploid 'Rwain',
Triploid 1 seedling of 'Horizon Monarch' x 'Rwain',
Triploid 1 seedling of 'Hotei' x 'Rwain',
Tetraploid 'Horizon Monarch',
Tetraploid 'L'Engin',
Tetraploid 'Lem's Monarch',
Tetraploid 'Marnius Koster',
Tetraploid 3 seedlings of 'Horizon Monarch' x 'Rwain',
Tetraploid 4 seedlings of 'Rwain' X 'L'Engin'
Source Marc Colombel
Note: R W A I N is short for Rhododendron Without An Important Name
John and Sally Perkins
