Greenhouse selection for black spot resistance in roses

Disease resistance is an important trait in new rose cultivars. Methods to screen for rose disease resistances during breeding and selection are needed. Black spot (Diplocarpon rosae) is one of the most occurring diseases in garden roses. To be able to select for better resistance, procedures to inoculate rose seedlings with black spot in the greenhouse were established. Black spot needs a prolonged period of leaf wetness for conidia germination and humid conditions for further development. Greenhouse circumstances were adapted to establish an ideal microclimate for infection. Therefore, seedlings were covered with a plastic tent after inoculation and plants were watered on top off the leaves to increase humidity. To optimize the inoculation and screening procedure different conidial concentrations and the effect of repeated inoculations were tested. Also the best inoculation moment during the growing season was determined. A practical protocol for greenhouse inoculation and resistance screening in the first year of rose selection is discussed.