Breeding for disease resistance is an important objective in Brassica crop improvement. In this study, we evaluated the applicability of previously published molecular markers associated with downy mildew resistance in Brassica oleracea genebank material. Phenotypic resistance data were obtained from previous inoculation experiments with Hyaloperonospora parasitica isolates. A subset of 313 individual plants from 115 Brassica accessions, representing different resistance phenotypes at the cotyledon stage, was selected for molecular analysis. Five SSR markers associated with the resistance loci Pp523, Ppa207, and Ppa3 were tested: CB10028, CB10139, BoGMS0900, BoGMS0486, and BoGMS0624. The SSR markers amplified 29 alleles across the analysed material. However, marker–phenotype associations were not fully consistent across crop types and accessions. The highest informativeness was observed for CB10028 and BoGMS0900, whereas other markers showed stronger dependence on genetic background. Our results indicate that published resistance-linked markers can provide useful information for Brassica germplasm characterization, but they cannot be used as universal predictors of downy mildew resistance without further validation in defined genetic backgrounds and against individual pathogen isolates. The present marker evaluation is limited to cotyledon-stage resistance phenotypes, and further phenotyping would be required to assess marker applicability to true-leaf or adult-plant resistance.
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