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United States Department of Agriculture

Agricultural Research Service

Title: Resistance to Powdery Mildew in Hydrangea

Authors
item Li, Yonghao - UNIV OF TENN
item Windham, Mark - UNIV OF TENN
item Trigiano, Robert - UNIV OF TENN
item Windham, Alan - UNIV OF TENN
item Reed, Sandra
item Mmbaga, Margaret - UNIV OF TENN
item Spiers, James
item Rinehart, Timothy

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2007
Publication Date: July 1, 2007
Citation: Li, Y., Windham, M., Trigiano, R., Windham, A., Reed, S.M., Mmbaga, M., Spiers, J.M., Rinehart, T.A. 2007. Resistance to Powdery Mildew in Hydrangea. Hortscience. pp.919-1022.

Interpretive Summary: Powdery mildew, caused by Erysiphe polygoni, is an important foliar disease of hydrangeas. Infection process and development of E. polygoni on hydrangeas were determined using a leaf disk assay. On susceptible hydrangea cultivars, conidia of E. polygoni germinated and formed primary appressoria within 6 h after inoculation. Secondary germ tubes were initiated from the primary appressoria or other parts of conidia. Lateral appressoria formed from hyphae that originated from germ tubes. Conidia in chains were observed on fungal colonies 5 days after inoculation. Significant differences in fungal development were detected among hydrangea cultivars. In this study, cultivar 'Veitchii' was resistant, 'Nikko Blue' was susceptible, and 'Madame Emile Mouilliere', 'Forever Pink', 'Lilacina' and 'Holstein' were intermediate. Resistance response to powdery mildew in 'Veitchii' was manifested as significantly fewer germinated conidia with branched hyphae, lower value of infection efficiency and less sporulation compared to the susceptible and intermediate cultivars. Latent period was significantly longer on 'Veitchii' than on susceptible cultivar 'Nikko Blue', but there was no significant difference in latent period between resistant and intermediate cultivars. Compared to the susceptible cultivar 'Nikko Blue', resistance to powdery mildew in intermediate and resistant cultivars was conditioned by all four of these resistance components.

Technical Abstract: Powdery mildew, caused by Erysiphe polygoni, is an important foliar disease of hydrangeas. Infection process and development of E. polygoni on hydrangeas were determined using a leaf disk assay. On susceptible hydrangea cultivars, conidia of E. polygoni germinated and formed primary appressoria within 6 h after inoculation. Secondary germ tubes were initiated from the primary appressoria or other parts of conidia. Lateral appressoria formed from hyphae that originated from germ tubes. Conidia in chains were observed on fungal colonies 5 days after inoculation. Significant differences in fungal development were detected among hydrangea cultivars. In this study, cultivar 'Veitchii' was resistant, 'Nikko Blue' was susceptible, and 'Madame Emile Mouilliere', 'Forever Pink', 'Lilacina' and 'Holstein' were intermediate. Resistance response to powdery mildew in 'Veitchii' was manifested as significantly fewer germinated conidia with branched hyphae, lower value of infection efficiency and less sporulation compared to the susceptible and intermediate cultivars. Latent period was significantly longer on 'Veitchii' than on susceptible cultivar 'Nikko Blue', but there was no significant difference in latent period between resistant and intermediate cultivars. Compared to the susceptible cultivar 'Nikko Blue', resistance to powdery mildew in intermediate and resistant cultivars was conditioned by all four of these resistance components.

Last Modified: 11/24/2014
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