An updated host differential due to two novel races of diplocarpon rosae wolf, the causal agent of rose black spot disease

David C. Zlesak, Darcy Ballantyne, Matthew Holen, Andrea Clark, Stan C. Hokanson, Kristen Smith, Jason D. Zurn, Nahla V. Bassil, James M. Bradeen

Research output: Contribution to journalArticlepeer-review


The fungal pathogen, Diplocarpon rosae, infects only roses (Rosa spp.) and leads to rose black spot disease. Rose black spot is the most problematic disease of outdoorgrown roses worldwide due to the potential for rapid leaf chlorosis and defoliation. Eleven races of the pathogen were previously characterized from isolates collected in North America and Europe. Isolates of D. rosae obtained from infected leaves of the roses Brite EyesTM ('RADbrite'; isolate BEP; collected in West Grove, PA) and Oso Easy® Paprika ('CHEwmaytime'; isolate PAP; collected in Minneapolis, MN) proved to have unique infection patterns using the established host differential with the addition of Lemon FizzTM ('KORlem'). The new races are designated race 12 (BEP) and race 13 (PAP), respectively, and Lemon FizzTM should be included in the updated host differential because it distinguishes races 7 and 12. Additionally, inconsistent infections and limited sporulation were found in the host differential Knock Out® ('RADrazz') for races 7 and 12. Expanding the collection of D. rosae races supports ongoing research efforts, including host resistance gene discovery and breeding new rose cultivars with increased and potentially durable resistance.

Original languageEnglish (US)
Pages (from-to)1756-1758
Number of pages3
Issue number11
StatePublished - Nov 2020

Bibliographical note

Funding Information:
Received for publication 3 Feb. 2020. Accepted for publication 31 July 2020. Published online 23 September 2020. This work was funded by the U.S. Department of Agriculture/National Institute of Food and Agriculture Specialty Crop Research Initiative project ‘‘RosBREED: Combining Disease Resistance with Horticultural Quality in New Rosaceous Cultivars’’ under award no. 2014-51181-22378. We thank Bailey Nurseries and Star® Roses and Plants for the donation of roses. S.C.H. is the corresponding author. E-mail: hokan017@ This is an open access article distributed under the CC BY-NC-ND license (https://creativecommons. org/licenses/by-nc-nd/4.0/).


  • Defoliation
  • Disease resistance
  • Marssonina rosae
  • Rosa
  • Virulence

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