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Effects of Ontogenic Resistance upon Establishment and Growth of Uncinula necator on Grape Berries

May 2003 , Volume 93 , Number  5
Pages  556 - 563

Andrea Ficke , David M. Gadoury , Robert C. Seem , and Ian B. Dry

First, second, and third authors: Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; and fourth author: CSIRO Plant Industry, Glen Osmond, SA 5064, Australia

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Accepted for publication 4 December 2002.

Grape berries become resistant to powdery mildew early in development and are nearly immune to infection within 4 weeks after bloom. In this study, ontogenic resistance did not reduce attachment, germination, or appressorium formation of Uncinula necator on 3- to 4-week-old berries of Vitis vinifera ‘Chardonnay’ or 3-week-old berries of V. labruscana ‘Concord’. Pathogen ingress halted at the cuticle before formation of a penetration pore. As berries aged, hyphal elongation and colony growth slowed until finally no secondary hyphae formed on fully resistant berries. More appressoria formed per unit of hyphal length as berries aged, indicating that failure to penetrate older berries led to increased attempts to penetrate resistant fruit. Additionally, hyphae within the colonies began to die as berries aged. Finally, the number of degree-hours between germination and sporulation of the colony (latent period) increased and sporophore density decreased with berry age at time of inoculation. Thus, ontogenic resistance both slows, and eventually halts disease development on grape berries, and limits the likelihood of spread by reducing absolute supply of conidia and delaying their formation. It furthermore has a consistent, stable, and predictable impact on grape powdery mildew and operates in a similar fashion and to a similar degree in both V. labruscana and V. vinifera, although at a slightly earlier phenological stage in V. labruscana.

Additional keywords: adult plant resistance, grape diseases, integrated pest management, Oidium.

© 2003 The American Phytopathological Society