Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Sordariomycetes
Subclass	Hypocreomycetidae
Order	Hypocreales
Family	Nectriaceae
Genus	Calonectria

Scientific Name

Calonectria cylindrospora

Scientific Name Synonyms

Cylindrocladium scoparium

Calonectria morganii

Common Name

Author: Alicyn Ryan, University of Florida

Reviewed by: Jeffrey Rollins, University of Florida

Pathogen

In the year 1892, A. P. Morgan was the first to describe the genus Cylindrocladium. He also described the type species for this genus scoparium (3). Cylindrocladium scoparium has a nonspecific, broad host range that encompasses 66 genera in 31 families of plants that are more commonly found in subtropical and tropical regions of the world (2). Economically important hosts include ornamental shrubs like azaleas, roses, and rhododendrons, as well as various trees including Cornus, Pinus, and Eucalyptus (6). Multiple row crops are also susceptible to this pathogen; some include peanuts, potatoes, soybeans, beets, strawberries, and watermelons. Cylindrocladium scoparium infection on these hosts can result in damping off, root rots and blights, stem lesions, leaf spots, defoliation, stunting and post-harvest fruit decays (1, 4).

Symptoms and Signs

Symptomology differ depending on the host infected by C. scoparium. In conifers, roots become necrotic. As the disease progresses, the epidermal tissue blackens and sloughs off when easily pulled. For hardwoods, the roots share these symptoms but also exhibit longitudinal cracking of the epidermis on the roots. As the roots become necrotic, the plant begins to decline until it eventually dies. Cylindrocladium scoparium causes stem lesions on Eucalyptus spp. that are typically found on the petiole. Eucalyptus spp. are also susceptible to stem canker formation, which has a high risk of girdling the plant, possibly killing the infected branch. In azaleas, leaf spots accompany root rot. Spots can cover up to 1/3 of the leaf. Under favorable conditions, the infected areas may look powdery due to conidiophore development. Conidia are 50-60 micrometers in length, 4.5-6 micrometers in width, and are cylindrical in shape with a single septation. The sexual state, Calonectria morganii, is less commonly observed (4). The conidiophores are typically scattered over the leaf surface of the infected plant and are about 0.5 µm in height and from 5-8 µm in width at the base. This species has a specific steril appendage that makes it easy to identify, known as the stipe. This is found in the main axis of the conidiophore and extends beyond the sporogenous zone. The stipe is approximately 27mm in length, 12mm in diameter, and is narrower below the swollen, apical vesicle, which is hyaline and ellipsoidal in shape (4).

Ecology and Spread

Cylindrocladium scoparium overwinters as microsclerotia and can survive for a multiple years in soil or on infected plant tissue. As the tissue debris begins to degrade in the soil, the microsclerotia are released. Germination of the microsclerotia is triggered when they come into contact with root excudates. Once germination is initiated, penetration of the root occurs within 24 hours. Septated hyphae colonize the root and begin to produce masses that form microsclerotia within several days. Under ideal conditions, the pathogen will produce the sexual stage (i.e., perithecia) on the upper portion of the root and crown. This orange colored structure contains asci that encapsulate ascospores and can be forcibly dispersed (2). Conidiophores are also produced on external plant tissue and form the asexual conidia that are wind and rain splash dispersed (4).

High humidity and rainfall are considered to be ideal for this pathogen considering the subtropic and tropic regions where it is most prevalent. Humidity is needed for the formation of the perithecium and for the discharge of the ascospores that can be forcibly released or as a viscous droplet during high humidity levels at day break. During rainfall, water droplets aid in disseminating ascospores when they splash on the perithecia. Both conidia and ascospores may be dispersed short distances via wind-blown plant debris, tillage practices, and pruning tools. The survival of the ascospores and conidia are reduced to 10% during normal day temperature and humidity within two minutes by desiccation (4).

Geographic Distribution

Cylindrocladium scoparium is considered to be a widely dispersed pathogen throughout North and South America, although identification and taxonomic confusion may have skewed actual distribution of this pathogen (7).

Management

Avoid planting in C. scoparium infested soils.
Limit the movement of plants to decrease the spread of the disease.
Rotate fields with non-susceptible hosts.
Till crop residue to degrade plant residue that may serve as inoculum.
Increase air movement through the plants by decreasing plant density or pruning.
Start transplants with disease free seedlings and inspect transplants in the greenhouse frequently.
Rogue any plants that appear unhealthy.
Reduce storage time of susceptable crops and keep storage temperatures at 1.6 - 4.4 degrees Fahrenheit.
Soak pots with 10% bleach for 30 minutes before reuse.
Use fungicide dips on roots for hardwoods and conifers to prevent disease.
Apply fumigants to row crops.
Use foliar sprays of fungicides to reduce progression of the disease for stem and leaf spots.
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 (4, 6).

Diagnostic Procedures

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

on PDA plates, colonies are a reddish-brown from the bottom of the plate with an irregular white margin;
with time, white mycelium becomes reddish-brown and produces abundant amounts of conidiophores; and
older plates develop microsclerotum that form in chains or clumps and can cause the culture to look black from the bottom of the plate.

Resources and References

1. Barnard E. L. 1984. Occurrence, impact, and fungicidal control of girdling stem cankers caused by Cylindrocladium scoparium on eucalyptus seedlings in a south Florida nursery. Plant Dis. 68 6:471-473. Compendium of Cucurbit Diseases. 1996.

2. Crous P. W. 2002. Taxonomy and pathology of Cylindrocladium (Calonectria) and allied genera. APS Press, St. Paul, Minn. 294.

3. Crous, P. W. and Wingfield, M. J. 1994. A monograph of Cylindrocladium, including anamorphs of Calonectria. Mycotaxon, 51, 341–435. http://www.cybertruffle.org.uk/cyberliber/index.htm

4. Howard, A. Cylindrocladium scoparium. www.cals.ncsu.edu/course/pp728/Cylindrocladium_scoparium/Cylindrocladium%20scoparium(1).htm.

5. L. Lombard, Crous, P. Wingfield, B. and Wingfield, M. 2010. Species concepts in Calonectria (Cylindrocladium). Stud Mycol. 66: 1-13.

6. R. M. Leahy. 1994. Cylindrocladium Root and Crown Rot of Roses. Fla. Dept. Agric. & Consumer Services-Division of Plant Industry. Plant Pathology Circular No. 364.

7. United States Department of Agriculture- Agricultural Research Service. http://nt.ars-grin.gov/fungaldatabases/new_allView.cfm?whichone=FungusHost&thisName=Cylindrocladium scoparium&organismtype=Fungus&fromAllCount=yes

Acknowledgements

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)