Rain-cracking of post-veraison grape berries (Vitis vinifera L.) reduces yield and quality of must and wine. Under vineyard conditions, cracking is often associated with bunch rots. The objective of ...the present study was to identify the role of Botrytis cinerea Pers.: Fr. as the dominant bunch rot fungus in cracking of Riesling berries. For these experiments grape berries with characteristic symptoms of Botrytis infections were selected in the vineyard. Berries infected by Botrytis always cracked in those regions of the berry where symptoms of the infections (brownish purple colour of the fruit skin) were present. In 55 % of these berries, cracks were orientated perpendicularly to the pedicel/stylar scar axis. Microscopic cracks referred to as microcracks were often present in the stylar scar region and occasionally in the vicinity of lenticels. These cracks allowed penetration of the fluorescent tracer acridine orange. The area infiltrated by the dye was positively related to crack length (r2 =#x003D; 0.43*). Water uptake of detached berries increased with time. Rates of uptake were highly variable and higher for infected berries as compared to berries without infections. Rates of water uptake into infected berries were positively related to cumulative crack length (number of cracks multiplied with average crack length) per berry (r2 =#x003D; 0.45*). Exposing the outer surface of the strained grape berry exocarp to water increased the frequency of microcracks. The increase was larger in infected berries than in those without symptoms. Our data demonstrate that Botrytis infections increase the cracking susceptibility of Riesling grape berries by weakening the grape berry exocarp, increasing crack length per berry which in turn resulted in increased water uptake.
PCR amplification of two
CHS gene fragments of the obligate biotroph
Plasmopara viticola, the causal agent of downy mildew of grapevine, is described. While one fragment shows homology to fungal ...class IV chitin synthases, the other fragment groups with other oomycete chitin synthases to form a novel class of chitin synthases most closely related to class I–III. RT-PCR experiments indicate that
PvCHS1 is constitutively expressed, whereas
PvCHS2 is specifically transcribed in sporangiophores and sporangia. Analyses of wheat germ agglutinin labeling patterns by confocal laser scanning microscopy show that chitin is present on the surface of hyphal cell walls during in planta growth, and of sporangiophores and sporangia.
Although Plasmopara viticola causes grape downy mildew in most, if not all, wine producing countries, many basic biological or chemical aspects are still unknown and thus the histopathological ...changes during development of this oomycete pathogen were studied. The fluorochromes Aniline blue and Uvitex 2B were successfully used in whole leaf stainings to visualise intercellular hyphae and to investigate septal-development in sporangiophores. The occurrence and transfer of cytoplasm in sporangiophores was studied with the aid of Chlorazole Black E and Phloxin B. Application of Chlorazole Black E was the most reliable method to differentiate between cytoplasm and septa in sporangiophores due to a high contrast between the dark cytoplasm and the pale septa. In P. viticola, septa were found in the stem and branches of the sporangiophores, but not in the intercellular hyphae, which was in contrast to other oomycetes, such as P. tabacina, Pseudoperonospora cubensis and P. humuli, where septa were frequently found in the mycelium. In order to verify chemical composition of septa, sporangiophores were digested using chitinase and β-1,3-glucanase. After staining with Aniline blue and Uvitex 2B, the intense fluorescence of septa was conserved after the application of chitinase but not after β-1,3-glucanase, indicating that septa are mainly composed of β-1,3-glucans. Pretreatments of infected vine leaves with 2-deoxy-D-glucose (2-DOG) at low concentrations (1–5 mM) led to a disorganisation of the sporangiophore structure of P. viticola, whereas the production of septa was unaffected. Application of 2-DOG at higher concentrations resulted in a reduced length of intercellular hyphae (10 mM) or total inhibition (50 mM) of the intercellular mycelium. Thus, 2 DOG or its analogues interferes with morphogenesis in Plasmopara viticola and may have a deleterious effect on the spread of this downy mildew between plants.
Abstract
PCR amplification of two CHS gene fragments of the obligate biotroph Plasmopara viticola, the causal agent of downy mildew of grapevine, is described. While one fragment shows homology to ...fungal class IV chitin synthases, the other fragment groups with other oomycete chitin synthases to form a novel class of chitin synthases most closely related to class I–III. RT-PCR experiments indicate that PvCHS1 is constitutively expressed, whereas PvCHS2 is specifically transcribed in sporangiophores and sporangia. Analyses of wheat germ agglutinin labeling patterns by confocal laser scanning microscopy show that chitin is present on the surface of hyphal cell walls during in planta growth, and of sporangiophores and sporangia.
Although
Plasmopara viticola causes grape downy mildew in most, if not all. wine producing countries, many basic biological or chemical aspects are still unknown and thus the histopathological ...changes during development of this oomycete pathogen were studied. The fluorochromes Aniline blue and Uvitex 2B were successfully used in whole leaf stainings to visualise intercellular hyphae and to investigate septal-development in sporangiophores. The occurrence and transfer of cytoplasm in sporangiophores was studied with the aid of Chlorazole Black E and Phloxin B. Application of Chlorazole Black E was the most reliable method to differentiate between cytoplasm and septa in sporangiophores due to a high contrast between the dark cytoplasm and the pale septa. In
P. viticola, septa were found in the stem and branches of the sporangiophores, but not in the intercellular hyphae, which was in contrast to other oomycetes, such as
P. tabacina, Pseudoperonospora cubensis and
P. humuli, where septa were frequently found in the mycelium. In order to verify chemical composition of septa, sporangiophores were digested using chitinase and β-1,3-glucanase. After staining with Aniline blue and Uvitex 2B, the intense fluorescence of septa was conserved after the application of chitinase but not after β-1,3-glucanase, indicating that septa are mainly composed of β-1,3-glucans. Pretreatments of infected vine leaves with 2-deoxy-D-glucose (2-DOG) at low concentrations (1-5 mM) led to a disorganisation of the sporangiophore structure of
P. viticola, whereas the production of septa was unaffected. Application of 2-DOG at higher concentrations resulted in a reduced length of intercellular hyphae (10 mM) or total inhibition (50 mM) of the intercellular mycelium. Thus, 2 DOG or its analogues interferes with morphogenesis in
Plasmopara viticola and may have a deleterious effect on the spread of this downy mildew between plants.
A crossing population was established to characterize quantitative trait loci of agronomically important traits and to elucidate basic principles of quantitative resistance in European type ...grapevine. Regent (female parent) copes well with fungal attack in field trials, whereas Lemberger (male parent) represents a traditional susceptible cultivar. The progeny comprising 153 individuals segregate for resistance to Plasmopara viticola and Uncinula necator and for other agronomic traits such as onset of berry ripening, bunch- and berry characteristics. Phenotypes were scored repeatedly for these quantitative traits over a period of six years. A dense linkage map of molecular markers (AFLP, RAPD, SSR, CAPS of characterized genes) was established for both parents using Mapmaker and Joinmap software under a high stringency of LOD8. These maps were aligned by anchor markers. In QTL interval mapping some of the traits under investigation showed reproducible and significant LOD score profiles. One objective of the project is to approach map-based cloning. To envisage this aim, marker fragments which map to QTL peak regions are currently under investigation.
Rain-cracking of post-veraison grape berries (Vitis vinifera L.) reduces yield and quality of must and wine. Under vineyard conditions, cracking is often associated with bunch rots. The objective of ...the present study was to identify the role of Botrytis cinerea Pers.: Fr. as the dominant bunch rot fungus in cracking of Riesling berries. For these experiments grape berries with characteristic symptoms of Botrytis infections were selected in the vineyard. Berries infected by Botrytis always cracked in those regions of the berry where symptoms of the infections (brownish purple colour of the fruit skin) were present. In 55 % of these berries, cracks were orientated perpendicularly to the pedicel/stylar scar axis. Microscopic cracks referred to as microcracks were often present in the stylar scar region and occasionally in the vicinity of lenticels. These cracks allowed penetration of the fluorescent tracer acridine orange. The area infiltrated by the dye was positively related to crack length (r super(2)=#x003D; 0.43*). Water uptake of detached berries increased with time. Rates of uptake were highly variable and higher for infected berries as compared to berries without infections. Rates of water uptake into infected berries were positively related to cumulative crack length (number of cracks multiplied with average crack length) per berry (r super(2)=#x003D; 0.45*). Exposing the outer surface of the strained grape berry exocarp to water increased the frequency of microcracks. The increase was larger in infected berries than in those without symptoms. Our data demonstrate that Botrytis infections increase the cracking susceptibility of Riesling grape berries by weakening the grape berry exocarp, increasing crack length per berry which in turn resulted in increased water uptake.Original Abstract: Das Platzen reifer Beeren der Weinrebe (Vitis vinifera L.) nach Niederschlaegen verursacht Verluste und Qualitaetseinbusen im Weinbau. Haeufig ist dies in der Spaetphase der Fruchtentwicklung mit einem Befall der Trauben mit Faeulnispilzen verbunden. In der vorliegenden Studie wird die Rolle des Grauschimmels (Botrytis cinerea Pers.:Fr.), der als dominierender Faeulniserreger auftritt, beim Platzen von Beeren der Sorte 'Riesling' untersucht. Hierzu wurden Weinbeeren mit charakteristischen Befallssymptomen (braun-violette Verfaerbung der Fruchthaut) des Pilzes nach natuerlicher Infektion am Standort ausgewaehlt. Nach Niederschlag platzten diese ausschlieslich in einem Bereich, in dem Befallssymptome vorlagen. Die Risse waren mehrheitlich, d. h. bei 55 % der Fruechte, quer zur Fruchtachse zwischen Stiel- und Griffelansatz orientiert. Auf der Fruchthaut von befallenen Weinbeeren traten gehaeuft in der Griffelregion und z. T. an Lentizellen mikroskopische Risse auf, die als Mikrorisse bezeichnet werden. Diese Risse zeigten nach Inkubation mit Acridinorange Infiltrationshofe unterschiedlicher Grose. Die infiltrierte Flaeche korrelierte positiv mit der Risslaenge (r super(2)=#x003D; 0,43*). Die Wasseraufnahme von abgeschnittenen Beeren stieg mit der Zeit an. Die Wasseraufnahmerate variierte stark, war fuer infizierte Beeren hoher als fuer solche ohne Symptome und korrelierte bei infizierten Beeren mit der kumulativen Risslaenge pro Beere (Produkt aus Anzahl der Risse pro Beere und mittlerer Risslaenge; r super(2)=#x003D; 0,45*). Durch Anwesenheit von Wasser auf der gespannten Fruchthaut wurden Mikrorisse induziert, deren Zahl in befallenen Beeren gegenueber solchen ohne Symptome um 55 % anstieg. Die Ergebnisse belegen, dass Botrytis-Befall die Platzempfindlichkeit von Weinbeeren der Sorte Riesling erhoht, insbesondere durch Schwaechung der Fruchthaut, einen Anstieg der Risslaenge pro Beere, wodurch sich eine erhohte Wasseraufnahme ergibt.
PDF
