Journal of Plant Pathology (2003) 85, 294-295

R. Musetti, L. Stringher, S. Borselli, A. Vecchione, F. De Luca, L. Zulini and I. Pertot (2003)
Ultrastructural analysis of Vitis vinifera leaf tissues showing atypical symptoms of downy mildew
Journal of Plant Pathology 85 (4), 294-295
X Meeting, Italian Society for Plant Pathology (poster)
Abstract: In a biodinamic farm of Tuscany a progressive regression of downy mildew outbreaks year after year and a decrease of the virulence, vigour and fertility of the causal agent (Plasmopara viticola) were observed. In particular, anomalous lesions caused by the fungus in leaf tissues of sensitive cultivars of Vitis vinifera were observed. These atypical symptoms were often associated with typical "oil spots" and occurred in favourable environmental conditions for a normal development of the disease. To understand the cause of this phenomenon, an ultrastructural study was carried out on grapevine leaf tissues to detect possible alterations of P. viticola mycelium and the possible presence of endophytes. Moreover, isolations were made on PDA medium from grapevine leaves by strip, washing the surface with sterile water, and sampling small leaf sections. Ultrastructural analysis by transmission electron microscope (TEM) showed that P. viticola hyphae were present in grape leaves showing typical "oil spot" symptoms: they were localized in the substomatal zone and in the intercellular spaces of spongy parenchyma and appeared generally vacuolated. Well-structured haustoria were also present. On the contrary, samples from atypical leaf symptoms had empty intercellular hyphae and necrotic haustoria, while the surrounding asymptomatic leaf tissues contained no hyphae and showed heavy cellular alterations (phenolic accumulation and chloroplast damage, dark material in the xylem, and fibrils differing from P-protein in the phloem). A number of bacteria, filamentous fungi, and yeasts were isolated from the leaf surface, while from inner leaf tissues fungi belonging to the genera Aspergillus, Fusarium, Alternaria, Stenphyllum, and Phoma were recovered. All these isolates were tested as possible antagonists of P. viticola, and showed different efficacy against the pathogen.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Ilaria Pertot

Research topic(s) for pests/diseases/weeds:
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Plasmopara viticola	Grapevine (Vitis)	Italy