Resistance to Marssonina rosae in Rosa L. seedlings obtained from controlled crosses including germplasm L83

Abstract

Blackspot is a serious disease on cultivated roses and resistance is rare; however, some wild Rosa species exhibit a high level of resistance. Disease incidence in field-grown offspring from three seedling families was evaluated as percentage of infected leaves (regardless of the size and number of spots) on each plant. Dolly, Queen Elizabeth and Friesia were used as pistillate parents and the resistant germplasm L83 (derived from the amphidiploid R. x kordesii) was the staminate parent. Assessments were performed during 3 years. Relative tolerance was seen in 71, 54 and 87%, respectively, of the individuals from the three different seedlings families. The infection pattern corresponded well to environmental factors such as precipitation. The importance of timing and duration of assessments over several years, as well as the correlation between blackspot infection and winter hardiness, are discussed.