John Perkins -American Rhododendron Society - A Novel Method for Identifying Suspected Triploids скачать в хорошем качестве

John Perkins -American Rhododendron Society - A Novel Method for Identifying Suspected Triploids

Talk presented at the Rhododendron Research Network 2025 Convention - A Novel Method for Identifying Suspected Triploids in Interploidy Contact Zones of Diploid Rhododendron canescens and Tetraploid Rhododendron austrinum. ABSTRACT For over 75 years triploids have been documented in interploidy contact zones involving tetraploid Rhododendron calendulaceum. The most common method of finding suspected triploids in an interploidy contact zone containing R. calendulaceum was to search for plants that had flower color atypical for both R. calendulaceum and the co-located diploid deciduous azalea species. This atypical flower color method worked well for finding triploids at Audra State Park near Buckhannon, West Virginia, Hurricane Creek near Dawsonville, Georgia, and Chattahoochee River National Recreation near Roswell, Georgia. However, flow cytometry also showed that triploids in such populations could have physical characteristics and flower colors typical for R. calendulaceum. In 2006 Dr. Ranney’s team determined using flow cytometry that R. austrinum, R. atlanticum, and R. colemanii as well as R. calendulaceum were tetraploids. Shortly thereafter, Ron Miller discovered that R. austrinum could have pink flowers. Moreover, within given populations of R. austrinum on the Escambia River, Blackwater River, and Yellow River, could have a range of flower colors from typical gold and yellows to combinations of yellow and pink to pink as well as white. These populations made using solely the atypical color rule impractical for finding triploids in interploidy contact zones involving R. austrinum and diploid pink R. canescens. However, our experience hand crossing diploid deciduous azaleas with tetraploid deciduous azaleas showed us the following: 1) Diploid X tetraploid normally produces viable seed; 2) Tetraploid X diploid does not normally produce seed pods; 3) Seedlings from diploid X tetraploid normally have the physically characteristics of the tetraploid pollen parent including flower color; 4) Seedlings from diploid X tetraploid are normally seed sterile triploids, and 5) Seedlings from diploid X tetraploid can be fertile triploids or fertile tetraploids. Both are rare occurring possibly 1 in every 100 seedlings. Ron Miller had observed based on field observations that tetraploid pink R. austrinum as well as tetraploid yellow R. austrinum have glands on the new growth whereas normally diploid pink R. canescens do not. From these observations our team formulated a method for finding triploids in interploidy contacts zones of diploid pink R. canescens with tetraploid R. austrinum that can be summarized as follows: Seedless triploids looking similar to typical glandular on the new growth R. austrinum will be found near large groups of typically nongranular on the new growth diploid pink R. canescens. The smaller the ratio of typical R. austrinum types to diploid pink R. canescent types the more likely the typical looking R. austrinum types are triploids especially if all the R. austrinum types are seedless whereas most of the diploid pink R. canescens have seed. This method allowed our team to locate triploids between R. canescens and R. austrinum in 8 locations in the Blackwater River State Forest, Yellow River Management area, and near Albany, Georgia. Triploids were, also, located in 2 additional interploidy contact zones involving R. austrinum using a combination of the above method with atypical flower color. All triploids were confirmed using flow cytometry.