Do ploidy levels play a role in disease resistance of roses?

Spontaneous polyploidisation is reported in many plant species in nature. A clear link between altered stress resistances and polyploidy is well studied in ecological context. In breeding polyploidisation is mostly associated with changes in plant morphology, yield, etc. Improving stress resistance by ploidy breeding is less exploited (also see poster: Breeding for polyploidy: examples in horticultural and agricultural crops). In the Polystress-project diploids and their tetraploid counterparts, obtained through polyploidisation, are compared for biotic and abiotic stress resistance. Crops tested are rose and apple. Drought stress is applied as an abiotic stress factor. Powdery mildew (Podosphaera pannosa) in rose and apple scab (Venturia inaequalis) in apple are biotic stresses tested. We present here first preliminary results and testing procedures to compare powdery mildew resistance in diploid and tetraploid rose genotypes. The rose genotypes used are hybrids from a diploid rose population segregating for resistance towards two rose powdery mildew pathotypes. In the diploids powdery mildew is well characterized through pathotype specific QTL-analysis on the genetic map of the rose population. For the comparison of powdery mildew resistance in the diploids and tetraploids, inoculation is performed using an inoculation tower and two powdery mildew pathotypes. Disease indexes are calculated per genotype and pathotype and for the different ploidy levels. Preliminary results of a first tests are shown. Further evaluation is necessary.