Ava Peterson

Rose black spot disease is caused by Diplocarpon rosae Wolf, a hemibiotrophic ascomycete fungus. This disease has been extensively researched because of the horticultural significance of roses. Previously researched isolates of D. rosae have been categorized into 13 races. Ramblin’ RedTM is a popular cultivar of climbing rose that has shown resistance to 9 out of 13 known races of D. rosae. However, recently, Ramblin’ RedTM has shown some irregular responses when inoculated with race 5 of D. rosae. In previous years, rose plants have remained in the greenhouse without a cold induced dormancy period. One potential explanation for the loss of resistance could involve the lack of dormant cold periods for the plants and the effect that this could have on specific resistant genes. We hypothesized that a lack of dormancy for the Ramblin’ RedTM population had affected its resistance to race 5 and that providing a cold treatment would restore its resistance. Three temperature treatment groups (4°c, 10°c, 21°c) were used to evaluate the effect of cold induced dormancy on Ramblin’ RedTM resistance to race 5. An additional race (race 11) that Ramblin RedTM remained resistant to despite the lack of cold induced dormancy was used as a positive control. Two separate inoculations were performed using detached leaf inoculations. The percentage of droplets infected and visual rating of sporulation were used to evaluate susceptibility of the plants 14 days post inoculation. This method allowed for a quantitative and qualitative assessment of the plants' susceptibility to D. rosae. Results from these experiments were inconclusive and suggested that no significant difference in susceptibility occurred between plants from each temperature treatment. It is important to note that confounding factors may have imposed plant stress that could have impacted results.