Reverse genetics strategies to obtain broad spectrum powdery mildew resistance in roses

Powdery mildew is a serious disease of greenhouse grown roses. For the economically important cut and pot roses around 20 fungicide treatments are needed to ensure high quality plant production. Genetic analyses of rose powdery mildew interactions have shown that, similar to other powdery mildew plant interactions, the fungus is highly variable. Although single dominant resistance genes and QTLs for resistance to powdery mildew have been characterized, resistance  breeding is hampered by complex breeding schemes for QTLs and a low durability of single genes. In contrast mutants in the barley MLO genes and in orthologous genes in Arabidopsis, tomato and pea display broad and durable resistance.  From an EST collection of 44000 ESTs generated by next generation sequencing, we isolated 30 MLO homologues of which four cluster closely to the “true” MLO genes of barley , Arabidopsis and tomato. In addition they also display typical amino acid motives for those MLO genes involved in plant powdery mildew interactions. First analyses of genetic variants of all four genes are currently investigated for mutations that would indicate a loss of function.