BIOASSAYS FOR RESISTANCE SCREENING IN COMMERCIAL ROSE BREEDING

Black spot (Diplocarpon rosae) and powdery mildew (Podosphaera pannosa syn. Sphaerotheca pannosa) are worldwide the most common diseases on roses.
Breeding towards resistance requires efficient bioassays to screen seedlings and parent plants for both diseases.
Screening of a collection of monoconidial cultures established from isolates collected in Belgium revealed the existence of powdery mildew pathotypes.
These pathotypes showed a differential response in virulence when tested on both in vitro rose and Prunus avium plantlets.
For both diseases, bioassays for resistance screening on rose seedlings were developed and applied in a commercial rose breeding program.
Resistance screening was used in the breeding program as one of the earliest selection criteria.
For these pathogens it is possible to enhance selection for resistant plants.