Botrytis cinerea is a necrotrophic fungus that affects many plant species, including wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or "gray mold".

The fungus gives rise to two different kinds of infections on grapes. The first, grey rot, is the result of consistently wet or humid conditions, and typically results in the loss of the affected bunches. The second, noble rot, occurs when drier conditions follow wetter, and can result in distinctive sweet dessert wines, such as Sauternes, the Aszú of Tokaji, or Grasă de Cotnari. The species name Botrytis cinerea is derived from the Latin for "grapes like ashes"; the "grapes" refers to the bunching of the fungal spores on their conidiophores, while "ashes" refers to the greyish colour of the spores en masse. The fungus is usually referred to by its anamorph (asexual form) name, because the sexual phase is rarely observed. The teleomorph (sexual form) is an ascomycete, Botryotinia fuckeliana, also known as Botryotinia cinerea (see taxonomy box).

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