HPIPM:Onion Post Harvest Decay

Author: Howard F. Schwartz

Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Gammaproteobacteria
Order	Enterobacteriales
Family	Enterobacteriaceae
Genus	Enterobacter

Scientific Name

Enterobacter cloacae

Common Name

Enterobacter bulb decay

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Eurotiomycetes
Subclass	Eurotiomycetidae
Order	Eurotiales
Family	Trichocomaceae
Genus	Aspergillus

Scientific Name

Aspergillus niger

Scientific Name Synonyms

Sterigmatocystis nigra

Common Name

black mold

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Leotiomycetes
Subclass	Leotiomycetidae
Order	Helotiales
Family	Sclerotiniaceae
Genus	Botrytis

Scientific Name

Botrytis aclada

Scientific Name Synonyms

Botrytis allii

Botrytis alli

Common Name

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Eurotiomycetes
Subclass	Eurotiomycetidae
Order	Eurotiales
Family	Trichocomaceae

Scientific Name

Penicillium

Common Name

Penicillium fungi

BACTERIAL bulb infection can be observed while plants are in the field or in storage. Softening of the neck may be observed and bulb tissue may appear translucent or water-soaked Most bacteria are favored by: • Harvest and storage temperatures above 30oC (86oF); some are favored by lower temperatures. • Free moisture and high humidity (greater than 75%) during production and harvest. • Planting of contaminated seed, transplants, sets Irrigation water; storm damage; excess nitrogen after bulb initiation; insects like thrips and maggots; and bruising during harvest

FUNGAL bulb infection can be observed while plants are in the field or in storage. Softening of the neck may be observed and bulb tissue may become covered by moldy, fungal growth. Common diseases include: Fusarium basal rot starts in the field and can progress in storage from a dry basal plate rot to a dry rot of the fleshy scales.

Black mold develops as black discoloration (usually at the neck), shallow lesions on outer scales, streaks of black mycelium and conidia beneath the outer dry scales, and black discoloration in bruised areas. Bulbs usually do not rot, unless secondary bacterial infection occurs.

Gray mold (neck rot) develops as a semi-watery decay, usually in the neck, that progresses down through the bulb. Fleshy scales soften and become water-soaked and translucent, with white to gray mycelium between scales. Gray to black sclerotia and gray mold may form on outer and inner scales.

Blue mold first appears as pale yellow blemishes, watery soft spots, and occasionally purple-red stain on scales. A green to blue mold may develop on the surface of lesions, there may be a light tan or gray color on the fleshy scales, and bulbs may become tough (punky) with a musty odor.

Factors Favoring: • Black mold is favored by harvest and storage >24oC (75oF); blue and gray molds, and Fusarium basal rot are favored by lower temperatures. • These diseases are favored by free moisture and high humidity (>75%) during harvest and storage. • These diseases are also favored by planting infected seed, transplants or sets; crop injury; and bruising of bulbs.

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