Gachomo, Emma Wanjiru: Studies of the life cycle of Diplocarpon rosae Wolf on roses and the effectiveness of fungicides on pathogenesis. - Bonn, 2005. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Emma Wanjiru Gachomo}},
title = {Studies of the life cycle of Diplocarpon rosae Wolf on roses and the effectiveness of fungicides on pathogenesis},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2005,
note = {The blackspot disease of roses caused by Diplocarpon rosae Wolf teleomorph (anamorph Marssonina rosae) is a widespread and important disease on outdoor grown roses. The development of D. rosae in rose leaves is not clearly understood and no detailed well-documented photographs of the fungus development in the host are available. The control of this pathogen heavily relies on fungicides. The objective of this study was to provide a detailed growth pattern the D. rosae inside the rose leaves and to test the effectiveness of fungicides, the strobilurins and azoles, on the various fungal structures formed by this fungus.
The aggressiveness of various Kenyan and Germany isolates was investigated. A German isolate was used to study the life cycle of D. rosae. The life cycle of the fungus was studied using different staining techniques for the light microscopy and the conventional preparation for electron microscopy: A conidium germinated to form a germ tube, from which an appressorium was sometimes formed. A brown ring that was presumably melanized was formed at the point of penetration of the host cuticle. Upon penetration an infection vesicle was formed in the subcuticular region. Primary hyphae spread from the infection vesicle into the subcuticular and intercellular regions in the host. The subcuticular, intercellular and intramural hyphae formed haustoria of varying shapes in the epidermal cells. The intercellular hyphae also formed haustoria in palisade mesophyll cells. Intracellular hyphae were formed just before the formation of the reproduction structures. Brown heavily ornamented structures formed in the overwintering leaves, opened in spring of the following year to release small thin-walled structures. No ascospores were formed in the subepidermal apothecia-like structures. The strobilurins completely inhibited germination of the conidia of D. rosae but the azoles did not. The azoles were able to destroy the fungal structures in the host even when they were applied after the fungus was fully established in the host but the effectiveness of the strobilurins was limited. Protective and curative tests of the effectiveness of the fungicides were carried out with 100 ppm of the active ingredients.
The study showed that D. rosae is a hemibiotroph: The biotrophic phase is marked by the formation haustoria and the necrotrophic phase by the formation of the intracellular hyphae. The weather conditions in Germany may not be suitable for the development of the ascospores in the subepidermal apothecia. The strobilurins were only effective when applied protectively. The azoles were effective when applied pre and post inoculation.},

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