Characterizing and identifying black spot resistance genes in polyploid roses

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: Journal of the American Society for Horticultural Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2018
Publication Date: 7/29/2018
Citation: Zurn, J.D., Zlesak, D.C., Holen, M., Bradeen, J., Hokanson, S.C., Bassil, N.V. 2018. Characterizing and identifying black spot resistance genes in polyploid roses. Abstract for the American Society for Horticultural Science Conference; 2018 July 31-August 3; Washington, DC.

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. Disease responses and genetic mapping are also under investigation in another family generated from a cross between two black spot resistant parents High Voltage and Lemon Fizz. These two varieties are resistant for different strains of black spot.

Technical Abstract: The ornamental quality of outdoor grown roses (Rosa hybrida) is under constant threat from foliar diseases, such as black spot caused by Diplocarpon rosae. Fungicides are primarily used to manage black spot; however, there is a high consumer demand for disease resistant roses which eliminate the need for chemical inputs. Phenotyping with 12 D. rosae races was conducted to better characterize resistance in four popular polyploid rose cultivars (Brite EyesTM, High VoltageTM, Lemon FizzTM, and Morden Blush). Subsequently, two populations (‘Morden Blush’ × Brite EyesTM and High VoltageTM × Lemon FizzTM) were developed to study resistance segregation and map the genes mediating black spot resistance using the rose Axiom array. ‘Morden Blush’ was susceptible to all races while the remaining three cultivars displayed differing disease responses. A 1:1 segregation ratio was observed for the two populations where each individual was either resistant or susceptible to all races tested to date, suggesting resistance is conferred by a single resistance gene in Brite EyesTM and Lemon FizzTM. High VoltageTM is expected to have a different resistance gene than Brite EyesTM and Lemon FizzTM based on observed disease responses. Linkage mapping in the ‘Morden Blush’ × Brite EyesTM population identified a single resistance gene that mapped to a chromosome 5 homeolog (Rdr4). To date, three black spot resistance genes, Rdr1, Rdr2, and Rdr3, have been identified. Rdr1 and Rdr2 both map to chromosome 1 indicating they are not allelic to Rdr4 and the location of Rdr3 is currently unknown. D. rosae races 3 and 9 are virulent on Rdr3 but avirulent on Rdr4. As such, we cannot confirm if Rdr4 is a unique gene or an allele of Rdr3. Future work will focus on developing tools for marker assisted breeding and pyramiding the identified resistance genes into new cultivars.