|Windham, M. -|
|Mmbaga, Margaret -|
|Windham, A. -|
|Li, Y. -|
Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2010
Publication Date: June 1, 2011
Citation: Windham, M.T., Reed, S.M., Mmbaga, M., Windham, A.S., Li, Y., Rinehart, T.A. 2011. Evaluation of Powdery Mildew Resistance in Hydrangea macrophylla. Journal of Environmental Horticulture. 29(2):60-64. Interpretive Summary: Bigleaf hydrangea (Hydrangea macrophylla) is a popular ornamental shrub that is cultivated both as a garden and a pot plant. Powdery mildew can be a significant problem on bigleaf hydrangea in the landscape during late summer to fall and during greenhouse propagation or production of potted plants. While powdery mildew usually does not kill plants in landscape settings, it does reduce the aesthetic quality of the plants. Powdery mildew resistance was evaluated in 90 cultivars of H. macrophylla over a 3-year period. ‘Amagi Amacha’ and ‘Veitchii’ were identified as the best cultivars for use in breeding powdery mildew resistant bigleaf hydrangea. ‘Diadem’ and ‘Omacha’ were also identified as potentially useful sources of resistance. Results of this study will be useful in breeding powdery mildew resistant H. macrophylla.
Technical Abstract: Powdery mildew, Erysiphe polygoni DC, can be a significant problem on Hydrangea macrophylla (Thunb.) Ser. in the landscape during late summer to fall and during greenhouse propagation or production of potted plants. Because very little information related to sources of resistance is available, 90 H. macrophylla cultivars were evaluated for resistance to powdery mildew over a 3-year period. This included 69 H. macrophylla ssp. macrophylla and 18 H. macrophylla ssp. serrata (Thunb.) Makino cultivars, along with three cultivars that are hybrids between the two subspecies. Significant differences among cultivars were found in all 3 years of the study. Three cultivars, ‘Amagi Amacha’, ‘Shirofuji’ and ‘Veitchii’, were among the most resistant each year. ‘Diadem’, ‘Komachi’, ‘Miyama-yae-Murasaki’, and ‘Omacha’ were highly resistant in 2006 and 2008, but only moderately resistant in 2007. ‘Komachi’, ‘Miyama-yae-Murasaki’ and ‘Shirofuji’ were considered unsuitable for breeding purposes as they do not appear to produce fertile flowers. ‘Veitchii’ was the only member of H. macrophylla ssp. macrophylla with a high level of powdery mildew resistance; while all other resistant cultivars were members of H. macrophylla ssp. serrata, not all members of this subspecies are resistant. Using host plant resistance is the desired method of providing protection to powdery mildew in bigleaf hydrangea; the information provided in this report should be useful in developing such a breeding program.