Mapping the black spot resistance locus Rdr3 in the shrub rose 'George Vancouver' allows for the development of improved diagnostic markers for DNA-informed breeding

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: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2020
Publication Date: 3/12/2020
Citation: Zurn, J.D., Zlesak, D.C., Holen, M., Bradeen, J.M., Hokanson, S.C., Bassil, N.V. 2020. Mapping the black spot resistance locus Rdr3 in the shrub rose 'George Vancouver' allows for the development of improved diagnostic markers for DNA-informed breeding. Theoretical and Applied Genetics. 133:2011-2020. https://doi.org/10.1007/s00122-020-03574-4.
DOI: https://doi.org/10.1007/s00122-020-03574-4

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 four resistance genes have been characterized. One of these genes, Rdr3, was identified by never mapped to a genetic location due to the complex genetics displayed in roses. Because of this we do not know if Rdr3 is a unique gene or a varient of one of the other known genes. New tools have recently been developed that has allowed us to finally map the position of Rdr3 on to chromosome 6 confirming its uniquness. Additionally three new DNA-based tools were developed to allow breeders to identify individuals with Rdr3. Out of 63 individuals examined in the study 13 were found to have Rdr3 and 11 black spot resistant rose varieites were identified that likely have an unknown source of resistance.

Technical Abstract: Diplocarpon rosae, the cause of rose black spot, is one of the most devastating foliar pathogens of cultivated roses (Rosa spp.). There is great potential for this globally distributed pathogen to cause large economic losses in the outdoor cultivation of roses. While the primary method of disease control is fungicides, they are viewed unfavorably by home gardeners due to potential environmental and health impacts. Planting rose cultivars with genetic resistance to black spot can reduce many of the fungicide applications needed in an integrated pest management system. To date, only four resistance genes have been identified in roses (Rdr1, Rdr2, Rdr3, and Rdr4). Rdr3 was never mapped and is thought to be unique from Rdr1 and Rdr2. It is unknown if it is an allele of Rdr4. To assess the novelty of Rdr3, a mapping population was created by crossing the Rdr3 containing cultivar George Vancouver with the susceptible cultivar Morden Blush. The mapping population was genotyped with the WagRhSNP 68K Axiom array and mapped using the ‘polymapR’ package. Rdr3 was mapped to a chromosome 6 homolog confirming it is different from Rdr1 and Rdr2, found on chromosome 1, and from Rdr4, found on chromosome 5. The new mapping information was used in conjunction with the Rosa chinensis genome assembly to develop new tightly-linked simple sequence repeat markers for marker assisted breeding. Three markers were able to predict the presence of Rdr3 in a 62-cultivar validation set. Additionally, 11 cultivars were appear to have resistance genes other than Rdr3. The improved diagnostic markers will be a great asset to the rose breeding community toward developing new black spot resistant cultivars.