Quantitative trait loci associated with resistance to powdery mildew in cornus florida

Authors: PARIKH, LIPI - Tennessee State University; MMBAGA, MARGARET - Tennessee State University; MERU, GEOFFERY - University Of Florida; ZHANG, GUORONG - Kansas State University; MACKASMIEL, LUCAS - Tennessee State University; Wadl, Phillip; Wang, Xinwang; TRIGIANO, ROBERT - University Of Tennessee

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2017
Publication Date: 9/12/2017
Citation: Parikh, L., Mmbaga, M.T., Meru, G., Zhang, G., Mackasmiel, L., Wadl, P.A., Wang, X., Trigiano, R.N. 2017. Quantitative trait loci associated with resistance to powdery mildew in cornus florida. Scientia Horticulturae. 226:322-326.

Interpretive Summary: Flowering dogwood (Cornus florida) is a popular ornamental tree species that is native to the eastern United States. Production of flowering dogwood has been negatively affected by powdery mildew, which is one of the most destructive diseases in the nursery. Conventional breeding for resistance to powdery mildew is a slow and laborious process because of the long life cycle of the tree. To date, there has been some success in breeding for powdery mildew resistance and there are a few cultivars that are resistant. Another hurdle for breeding progress is the labor and space needed to visually evaluate hybrid seedlings for response to powdery mildew infection. The advent of DNA markers has allowed researchers to speed up the breeding and selection process by identifying DNA markers that are associated with a trait of interest. Our objective in this study was to identify DNA markers that were associated with powdery mildew resistance in flowering dogwood. Controlled crosses were made to develop populations that segregated for powdery mildew resistance. The experimental populations were visually rated for powdery mildew resistance and genotyped with DNA markers. Data from the powdery mildew ratings and DNA markers were statistically analyzed and the results indicated that there were four DNA markers associated with powdery mildew resistance. This study provides an important first step towards the application of marker-assisted selection for powdery mildew resistance in flowering dogwood.

Technical Abstract: 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 the susceptible cultivar ‘Cherokee Princess’(CP), and powdery mildew resistant lines or selections R14 and MI9. The two pseudo-F2 populations (CP x R14, n= 147 and CP x 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 application of marker-assisted selection (MAS) for the improvement of powdery mildew resistance in flowering dogwood.