Genus/species (aliases): Botrytis cinerea (Noble rot or Grey/Vulgar rot)
Classification: Ascomycete; occurs mainly in anamorphic form
- Cell: filamentous
- Spore: conidia on conidiophores (asexual spores). Conidiophores 2mm or more long and can be 16-30µm wide.
- Zygote: NA
- Ascus: NA
- Liquid Growth: Spores air dispersed and also transmitted by rain droplets
Over winters as mycelia and sclerotia on grape mummies or on cuttings. Condidia are produced on condidaphores and can be dispersed by wind and or rain. They can land and germinate on damaged tissue or on microlesions. Botrytis produces laccase which is an enzyme that will catalyze phenolic oxidation reactions and cause browning. This is accomplished by the conversion of non-flavonoid phenolic compounds such as caffeic and p-courmaric acids to quinines by the laccase. Botyrits also produces lytic enzymes, lipases, pectinases, that allow penetration of plant epidermis. Additionally high levels of lactic and acetic acid, is often found in wines produced with infected grapes. Polyols are also often produced, especially glycerol. Glycerol is often higher in noble rot wines, as it may be broken down in metabolic reactions by bacteria in Grey rot infections.
Commonly found on grapes but there is a wide host range for botrytis cinerea including many fruits vegetables, and flowers. On grape berry surface the stomata have peristomatic areolas that form microlesions. These microlesions offer entry point for botrytis cinerea. This begins with attachment, condida development and then penetration.
Noble rot has unique star pattern on the grape berry surface. Grey rot results in the total degradation and collapse of berry tissue. Conidiophores grow straight out and upright and lend a soft velvety appearance to the necrotic tissues. Also can detect by analysis of laccase enzyme activity by kits or wine expose to oxygen, and immunochemical assay kits. Zoecklein suggests exposing wine to oxygen for several hours and observing for subsequent loss of red color and browning reactions
In the vineyard, canes may show bleaching with black sclerotia forming spots on affected tissue.
Role in wine:
Noble rot is commonly used to produce Sauternes in France, Trokenbeerenausleses and Tokay Asza wines in Hungary by over maturation. If climatic conditions are not favorable (cold and wet climates) grey rot will result and secondary infections by other common mold in the vineyard will out compete the botrytis cinerea. These include Penicillium, Mucor, and Aspergillus sp.
- SO2: X
- DMDC: X
- Heat: X
- Edwards, C. 2005. Illustrated guide to microbes and sediments in Wine, Beer and Juice.
- Kurtzman, C. and Fell, J. 1998. The Yeasts, A Taxonomic Study.