Plant Pathology: Extension: Plant Disease Library

Botrytis

Important diseases: Gray Mold of vegetables, ornamentals, fruits, and field crops, Neck rot of onion, Blossom blight of numerous herbaceous ornamentals.

Botrytis diseases appear primarily as blossom blights and fruit rots, but the fungus also causes stem cankers, leaf blights and spots, and tuber and bulb rots. Botrytis readily colonizes weakened or dead tissues and often survives on decaying plant material. The disease spreads rapidly under high humidity conditions.

Under humid conditions, the fungus produces a gray to whitish-gray layer of hyphae and fungal fruiting structures (conidiophores and conidia) over the affected tissue. This layer gives the characteristic "gray mold" appearance of Botrytis infections. Infected flowers often have small white or translucent spots on colored petals and brown spots on white petals, with continued moisture the spots will grow together and a fuzzy gray mold will cover the rotten blooms. Leaf spots tend to be tan to darker brown with a zonate appearance. On onion, leaf spots are white surrounded by a light green halo. Stem cankers and damping-off symptoms are common on plants in greenhouses including ornamentals and vegetable transplants. Storage rot is common with Botrytis in which infected tissue is sunken, water-soaked and often covered with gray mold.

Conidiophores are tall, slender and may be clear or pigmented. The upper portion of the conidiophores is irregularly branched. The terminal cells are enlarged or rounded and bear clusters of conidia (spores).

Conidia are single celled, oval, and clear or grayish en mass. Botrytis also produces black survival structures called sclerotia which may or may not be present on infected tissue.