Mapping a novel black spot resistance locus in the climbing rose Brite Eyes™ (‘RADbrite’)

Authors: Zurn, Jason; ZLESAK, DAVID - University Of Wisconsin; HOLEN, MATTHEW - University Of Minnesota; BRADEEN, JAMES - University Of Minnesota; HOKANSON, STAN - University Of Minnesota; Bassil, Nahla

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2018
Publication Date: 11/26/2018
Citation: Zurn, J.D., Zlesak, D., Holen, M., Bradeen, J., Hokanson, S., Bassil, N.V. 2018. Mapping a novel black spot resistance locus in the climbing rose Brite Eyes™ (‘RADbrite’). Frontiers in Plant Science. 9:1730. https://doi.org/10.3389/fpls.2018.01730.
DOI: https://doi.org/10.3389/fpls.2018.01730

Interpretive Summary: Rose black spot is one of the most devastating diseases of cultivated roses for both the home and commercial market. The use of genetic resistance is the most economic and environmentally friendly management strategy for controlling the disease. Currently, little is known about resistance found in roses and only three resistance genes have been characterized. The variety Brite Eyes has been found to be resistant to all but one strain of the pathogen which causes black spot. To better characterize the resistance in Brite Eyes a family was developed by crossing it with the susceptible variety Morden Blush. Results of disease screening of this family indicates that the resistance is controlled by a single resistance gene. Subsequent genetic mapping identified a single resistance gene. The previously mapped resistance genes do not map to this location and do not provide resistance to many of the pathogen strains the Brite Eyes gene does. Therefore the resistance gene in Brite Eyes is a new gene.

Technical Abstract: Rose black spot, caused by Diplocarpon rosae, is one of the most devastating foliar diseases of cultivated roses (Rosa spp.). The globally distributed pathogen has the potential to cause large economic losses in the outdoor cultivation of roses. Fungicides are the primary method to manage the disease, but are often viewed unfavorably by home gardeners due to potential environmental and health impacts. As such, rose cultivars with genetic resistance to black spot are highly desired. The tetraploid climbing rose Brite EyesTM (‘RADbrite’) is known for its resistance to black spot. To better characterize the resistance present in Brite EyesTM, phenotyping was conducted on a 94 individual F1 population developed by crossing Brite EyesTM to the susceptible tetraploid rose ‘Morden Blush’. Brite EyesTM was resistant to all D. rosae races evaluated except for race 12. The progeny were either resistant or susceptible to all races (2, 3, 8, 9, 10, 11, and 13) evaluated. The segregation ratio was 1:1 ('2 = 0.3830, P = 0.5360) suggesting resistance is conferred by a single locus. The roses were genotyped with the WagRhSNP 68K Axiom array and the ‘polymapR’ package was used to construct a map. A single resistance locus (Rdr4) was identified on the long arm of chromosome 5 homeolog 4. Three resistance loci have been previously identified (Rdr1, Rdr2, and Rdr3). Both Rdr1 and Rdr2 are located on a chromosome 1 homeolog. The chromosomal location of Rdr3 is unknown, however, races 3 and 9 are virulent on Rdr3. Rdr4 is either a novel gene or an allele of Rdr3 as it provides resistance to races 3 and 9. Due to its broad resistance, Rdr4 is an excellent gene to introgress into new rose cultivars.