Taxonomy

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

Scientific Name

Botrytis cinerea

Scientific Name Synonyms

Botryotinia fuckeliana

Botrytis vulgaris

Sclerotinia fuckeliana

Common Name

gray mold

Author: Michelle S. Oliveira, University of Florida

Reviewed by: Jeffrey Rollins, University of Florida

Pathogen

Botrytis cinerea, a non-specific pathogen, that infects more than 400 hosts including several cultivated crops and many wild plants (2, 3, 4). Grey mold can develop fast and the disease can be devastating on the field, in greenhouses, and in post-harvest. Losses can be severe throughout the production system, at harvest, during transportation, selling, and after final sale.

The pathogen can also live as a saprophyte on necrotic, senescent, or dead tissue. Conidia are hyaline, one-celled, nonseptate, egg-shape (ovoid or globose) with dimensions 8.12 x 11.74 micrometers (variable), grey in mass. Conidiophores are produced directly from the hyphae and are stout (16-30 µm diameter), tall (1-5 mm long) dark brown, and irregularly branched. Sclerotia are the main survival structure, they are usually dark, discoid, firmly attached to the substrate, and with dimentions 2-4 x 1-3 mm. Apothecia is rarely found from the germination of the sclerotia. However, when present are cupulate, stalked and brownish, about 4-5 mm long, and produce hyaline, one-celled, ovoid-ellipsoid ascospores (7 x 5.5. µm) (2, 3, 4).

Symptoms and Signs

Symptoms on flowers and inflorescences vary from blight of the blossom to a complete rot and drop. On fruits, the symptoms start at the base of the calyx with a small round lesion that develops into a soft rot. The fruit becomes covered by a fuzzy mass of grey spores (4), characteristic of the disease. Senescent leaves and stems can also be infected, developing a water-soaked brownish grey soft rot (3). Infected leaves and stems serve as a source of inoculum for new flowers and fruits. Other observed symptoms include: damping-off, stem canker, leaf spots, and tuber, corm, bulb, and root rot (1).

Ecology and Spread

The fungus survives on the soil in the form of sclerotia, on a saprophytic interaction with the plant debris, or as a latent infection in plant tissues. Sclerotia will germinate at temperatures from 3-27 degrees Celsius to produce mycelium (2, 4). Conidiophores produced directly from the hyphae form conidia, which are dispersed by wind, water splash and irrigation. Cool and humid weather are perfect for the germination of conidia on plant tissues, with temperatures around 1-30 degrees Celsius (optimum 18 degrees Celsius). Conidia directly penetrate or will penetrate through wounded tissues. Infection occurs in the presence of free water or relative humidity higher than 90% for several hours, and is optimal at 15-25 degrees Celsius (2, 4). Infected cells collapse and disintegrate causing a soft rot and new conidiophores are formed showing the signs of grey mold. Repeated cycles of the disease will occur while there is a possible host in the field. Under adverse environmental conditions (i.e., high temperatures and low humidity), the fungus will produce new sclerotia and overwinter.

Geographic Distribution

Botrytis cinerea can be found worldwide.

Management

Eliminate plant debris and properly treat the soil before planting to diminish survival of B. cinerea.
Avoid the use of nitrogen fertilization during the cycle of the crop, as it can increase incidence of disease.
Provide aeration through crop leaves, preventing leaf wetness and humidity.
Avoid use of sprinklers to irrigate, reducing disease severity.
Store harvested fruits at low temperatures (0 degrees Celsius) to suppress growth of the pathogen.
Use an antagonistic fungus, Trichoderma harzianum, as a potential biological control (2, 4).
Use weather-based advisory systems to manage disease risk (e.g., Agroclimate).
Use chemical control if necessary. Important: Consult your local extension specialist for legal and efficacious fungicide products available in your state. Remember, the label is the law and the product applicator is responsible for reading and following all chemical labeling.

Diagnostic Procedures

Infected material can be microscopically examined or incubated at high humidity (i.e., moist chambers) in order to produce spores on leafs, petioles, and/or fruit lesions. Diagnostic features include:

presence of a fuzzy grey mass of spores;
dark branched tree-like conidiophores 1-3 mm long;
conidia are hyaline, nonseptate, ovoid or globose, with dimensions 8.12 x 11.74 micrometers; and
possible presence of sclerotia (2-4 x 1-3 mm) on the culture media.

This fungus will grow well on common culture media such as PDA, but will sporulate better in MEA.

Molecular diagnostic methods are available, see NorgenBiotek®.

Resources and References

1. Agrios, G.N. 2004. Plant Pathology. 5th edi. Academic Pr.

2. Compendium of Grapes Diseases. 1994. APS Press, St. Paul-MN.

3. Compendium of Lettuce Diseases. 1997. APS Press, St. Paul-MN.

4. Compendium of Strawberry Diseases. 1998. APS Press, St. Paul-MN.

Acknowledgments

National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)