Screening Ornamental Cherry (Prunus) Taxa for Resistance to Infection by Blumeriella jaapii

Ornamental flowering cherry trees are important landscape plants in the United States but are susceptible to several serious pests and disease problems. Cherry leaf spot, incited by the fungus Blumeriella jaapii, is characterized by defoliating susceptible trees in late summer, leading to weakening or even death of the tree. To identify resistant plants for use in landscape plantings and in our breeding program, we used a detached leaf assay to screen 69 diverse ornamental flowering cherry taxa for resistance to cherry leaf spot. We found clear differences in susceptibility among the accessions, with seven accessions developing essentially no symptoms at all. A variance decomposition showed that most of the variance (59%) occurred among accessions, indicating that genotype, even more than species, determined susceptibility. The detached leaf assay used in this study is an effective method for screening large numbers of plants for relative resistance to cherry leaf spot. These methods will be particularly useful to characterize germplasm and screen hybrids in breeding and selection programs.