Research PaperQuantitative trait loci associated with resistance to powdery mildew in Cornus florida

- QTL mapping was conducted using the microsatellite or simple sequence repeat (SSR) markers.
- QTL mapping identified four QTLs associated with powdery mildew disease resistance in Cornus florida.
- First study to identify genomic regions associated with resistance to powdery mildew in flowering dogwood.

Powdery mildew of flowering dogwood (Cornus florida) caused by Erysiphe pulchra is one of the most destructive diseases in nursery production of flowering dogwood throughout the southeastern U.S. since the mid-1990s. Efforts to breed for resistance to the disease have been undertaken, but to-date only a few resistant cultivars have been released. Conventional breeding for powdery mildew resistance is time-consuming because of the long generation time for the tree crop. Additionally, phenotyping for powdery mildew resistance is cumbersome and resource intensive. Molecular breeding targeting DNA markers tightly linked to powdery mildew resistance can improve selection efficiency in flowering dogwood breeding programs. Although a genetic map based on simple sequence repeats (SSR) is available for flowering dogwood, genomic regions associated with powdery mildew resistance have not been identified. The aim of the current study was to identify quantitative trait loci (QTLs) associated with powdery mildew resistance in flowering dogwood using segregating pseudo-F2 populations derived from crosses between a susceptible cultivar 'Cherokee Princess'(CP), and powdery mildew resistant lines or selections R14 and MI9. The two pseudo-F2 populations (CP × R14, n = 147 and CP × MI9, n = 147) were phenotyped for powdery mildew resistance in the greenhouse and genotyped using 105 simple sequence repeats (SSR) or microsatellite markers. Four QTLs (R2 = 9.5%-13.2%) were identified in the two populations on linkage groups 4, 5, and 9. This study provides the first step towards marker-assisted selection (MAS) for the improvement of powdery mildew resistance in flowering dogwood.