Colletotrichum orbiculare (anthracnose of cucurbits)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Sordariomycetes
Subclass	Hypocreomycetidae
Order	Glomerellales
Family	Glomerellaceae
Genus	Colletotrichum

Scientific Name

Colletotrichum orbiculare

Scientific Name Synonyms

Colletotrichum lagenaria

Colletotrichum lagenarium

Glomerella lagenaria

Common Name

anthracnose

Author:Tom Creswell, Purdue University

Reviewed by: Dan Egel, Purdue University

Pathogen

Colletotrichum orbiculare is widely distributed in most regions where cucurbits are grown. The ascomycete state is rarely found in nature. Conidia are hyaline, nonseptate, mostly oblong and measure 4-6 x 13-19 micrometers.

Symptoms and Signs

Symptoms include leaf spots, fruit rot and seedling damage. Leaf lesions on watermelon tend to be angular but on cucumber and muskmelon they more rounded. Click on each image to see a larger view and read the captions.

Ecology and Spread

The fungus survives non-crop periods on infected plant residue and may be seed borne. Spores are spread by wind, rain, machinery and handling. Warm, wet weather is favorable for anthracnose infection and spread, with optimum temperatures of 26-32 degrees C. Symptoms often become severe when the plant canopy has developed sufficiently to provide consistently high humidity. Symptoms develop about 4 days after infection. Two races of the anthracnose fungus (Colletotrichum orbiculare) are common on cucurbit crops. Race 1 causes lesions on cucumber. Race 2 is responsible for lesions on watermelon. Muskmelon is generally more susceptible to race 1 than to race 2. Many watermelon cultivars are marketed as having resistance to anthracnose race 1, however there are currently no commercial watermelon cultivars that have resistance to race 2 of the anthracnose pathogen.

Geographic Distribution

Anthracnose is a fairly common problem on cucurbits in all humid growing regions.

Management

• Fall Tillage
• Rotate away from cucurbit crops for 3 years
• Host resistance exists in some cucumber varieties
• Start transplants with disease free seeds and inspect transplants in the greenhouse frequently
• Use fungicides to prevent disease at or before the time vines begin to touch within the row
• Do not save seeds from fields where anthracnose has been observed

Diagnostic procedures

Incubate fresh material to allow production of spores within leaf, petiole and fruit lesions. Diagnostic features:

• Presence of a pinkish to salmon mass of spores
• Black stroma
• Black setae
• Conidia are hyaline, nonseptate, oblong and 4-6 x 13-19 micrometers.

Resources and References

• Compendium of Cucurbit Diseases, APS Press, 1996.

Acknowledgements

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30818 as part of "Diagnostic Image Series Development for Supporting IPM in the North Central Region" (USDA-NIFA-RIPM-003349)

http://www.extension.purdue.edu/extmedia/BP/BP-180-W.pdf