Qualitative resistance conferred by major genes (Rdr genes) has been widely studied but quantitative resistance to BSD requires further investigation. However, in the actual context of reducing agrochemical use, the demand for rose bushes with higher levels of resistance has increased. is efficiently controlled with fungicides. The widespread rose black spot disease (BSD) caused by the hemibiotrophic fungus Diplocarpon rosae Wolf. Co-localization between R-genes and defense response genes was revealed via meta-analysis. Two environmentally stable QTLs linked to black spot disease resistance in the Rosa wichurana genetic background were detected, in different connected populations, on linkage groups 3 and 5. rosae races supports ongoing research efforts, including host resistance gene discovery and breeding new rose cultivars with increased and potentially durable resistance. Additionally, inconsistent infections and limited sporulation were found in the host differential Knock Out (‘RADrazz’) for races 7 and 12. 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. 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’). Eleven races of the pathogen were previously characterized from isolates collected in North America and Europe. Rose black spot is the most problematic disease of outdoor-grown roses worldwide due to the potential for rapid leaf chlorosis and defoliation. The fungal pathogen, Diplocarpon rosae, infects only roses (Rosa spp.) and leads to rose black spot disease. Due to its broad resistance, Rdr4 is an excellent gene to introgress into new rose cultivars. Rdr4 is either a novel gene or an allele of Rdr3 as it provides resistance to races 3 and 9. The chromosomal location of Rdr3 is unknown, however, races 3 and 9 are virulent on Rdr3. Both Rdr1 and Rdr2 are located on a chromosome 1 homoeolog. Three resistance loci have been previously identified (Rdr1, Rdr2, and Rdr3). A single resistance locus (Rdr4) was identified on the long arm of chromosome 5 homoeolog 4. The roses were genotyped with the WagRhSNP 68K Axiom array and the 'polymapR' package was used to construct a map. The segregation ratio was 1:1 (χ 2 = 0.3830, P = 0.5360) suggesting resistance is conferred by a single locus. The progeny were either resistant or susceptible to all races (2, 3, 8, 9, 10, 11, and 13) evaluated. rosae races evaluated except for race 12. To better characterize the resistance present in Brite Eyes TM, phenotyping was conducted on a 94 individual F1 population developed by crossing Brite Eyes TM to the susceptible tetraploid rose 'Morden Blush'. The tetraploid climbing rose Brite Eyes TM ('RADbrite') is known for its resistance to black spot. As such, rose cultivars with genetic resistance to black spot are highly desired. Fungicides are the primary method to manage the disease, but are often viewed unfavorably by home gardeners due to potential environmental and health impacts. The globally distributed pathogen has the potential to cause large economic losses in the outdoor cultivation of roses. Rose black spot, caused by Diplocarpon rosae, is one of the most devastating foliar diseases of cultivated roses (Rosa spp.).
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