2019 ASHS Annual Conference

Genetic mapping in polyploid organisms that undergo random pairing during meiosis can be a complex process. Early genetic maps were constructed using single dose allele markers that segregate 1:1. These markers are incapable of being used to identify homoeologous or ohnologous chromosomes. Recently, software capable of identifying allelic dosage for SNP markers and mapping software that allows for the use of higher-dose markers has become available. This has allowed for great advancements in the mapping of segmental allopolyploids, like hybrid roses. The black spot resistance gene Rdr3 was previously identified in the tetraploid rose ‘George Vancouver’ but has not been mapped. As such, a mapping population was developed by crossing ‘George Vancouver’ with the susceptible tetraploid rose ‘Morden Blush’. Phenotyping was conducted via a detached leaf assay with the Diplocaron rosae race 8 isolate ACT. The population was genotyped with the WagRhSNP 68K rose Axiom array and allelic dosages were called using the R package ‘fitPoly’. Genetic mapping was conducted using the R package ‘polymapR’, that allows for the use of single and higher-dose markers for triploid, tetraploid, and hexaploid populations. Rdr3 was mapped to a chromosome 6 homoeolog. To date, three additional black spot resistance genes have been mapped (Rdr1, Rdr2, and Rdr4). Both Rdr1 and Rdr2 map to a chromosome 1 homoeolog and Rdr4 maps to a chromosome 5 homoeolog. Because Rdr3 maps to a different region than any of the previously mapped genes, it is a unique gene and not an allele of the other genes. The mapping of Rdr3 demonstrates how new analysis tools can be used to create maps with much greater marker density for polyploids and begin answering some of the complex genetic questions surrounding them.