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Cylindrocladium parasiticum
A PP728 Class Project
by Anne Williams

Introduction:

This fungus was first noticed in the US in southwest Georgia in 1965 in peanut (Arachis hypogaea L.) fields and has since become widespread throughout peanut growing areas in the southeast . The disease is known commonly as Cylindrocladium black rot (CBR), or red crown rot (on soybean).

It is thought that the fungus was introduced from Asia during the establishment of a tea plantation in coastal Georgia in the 1950s. It is found in tropical and subtropical regions.

This fungus was originally identified by Bell and Sobers (1966) as that which was previously known as the anamorph of Cercosporella theae var. crotalariae, a common pathogen of tea (Theae sinensis L.) and crotalarias (Crotalaria spp.) in Asia. Bell and Sobers (1966) proposed raising this variety to the species level, and gave the name Calonectria crotalariae (Loos) Bell & Sobers to its perfect form and Cylindrocladium crotalariae to the imperfect form. It was subsequently decided that these names had not been validly published, and thus Crous et al. (1993) established the current name Cylindrocladium parasiticum Crous, Wingfield and Alfenas for the imperfect form. Crous et al. (1993) also determined that Calonectria ilicicola Boedign & Reitsma (1950) and Calonectria crotalariae Bell and Sobers (1966) were the same species, and thus the former name has priority for the teleomorph.

Cylindrocladium parasiticum Crous, M.J. Wingfield, & Alfenas
   Cercosporella theae var. crotalariae Loos, nom. inval.
   Cylindrocladium crotalariae (C.A. Loos) D.K. Bell & Sobers, nom. illeg.

Calonectria ilicicola Boedijn & Reitsma
   Calonectria crotalariae (Loos) D.K. Bell & Sobers
   Calonectria theae var. crotalariae C.A. Loos

Host Range and Distribution:

Cylindrocladium black rot has spread to all peanut-producing states in the US and can infect legumes generally in this region, especially soybean, as well as blueberry (Vaccinium ashei and V. corymbosum) tea (Camellia sinensis), yellow poplar (Liriodendron tulipifera), sweetgum (Liquidambar styraciflua) and other hardwood seedlings. It has recently been reported on the legume weeds patridgepea, sicklepod, and Florida beggarweed (Brenneman et al., 1998; Padgett et al., 1995). Cylindrocladium black rot is a a serious problem on eucalyptus (Eucalyptus spp.), crotalarias and tea in China, Japan, India and Australia (Porter et al., 1991).

Isolation:

Phipps et al. (1976) detailed an elutriation method for isolation of the pathogen from field soil. Griffin et al. (1978) evaluated the effects of various factors on viability of microsclerotia in samples, and concluded that maintaining samples at field moisture and temperature levels is critical. Bell and Sobers (1966) noted that the fungus can be grown successfully on PDA, that perithecial development was enhanced by exposure to fluorescent light, and that optimum mycelial growth occurred at 26-28 ° C.

Identification:

C. ilicicola is an ascomycete in the Pyrenomycete group. The fungus is homothallic, and produces orange-red perithecia, 300-500 m m high and 280-400 m m wide, oval to round or obovate with large, irregular and thin-walled cells. Asci are clavate and have eight falcate spores with 1-3 septae. In contrast, microsclerotia have dark brown, thick-walled cells (Hwang, and Ko, 1976). Conidia are cylindrical, hyaline, have 1 - 3 septae, and are produced by apical budding; they have been measured between 38-68 x 4-5 m m. Vesicles are clavate and 5-10 m m wide. Conidiophore-bearing stipes appear at right angles from the host. Detailed descriptions are given in Crous et al. (1993) and Bell and Sobers (1966).

Symptoms and Signs:

On peanut: the pathogen can infect any below-ground tissue, but the region immediately behind the root tips is the primary infection court. Taproots and hypocotyls become blackened and necrotic, with necrosis terminating at ground line. Root tips are sloughed off, leaving stubs. Sunken, blackish lesions appear on roots, pegs, and pods. Leaf tips and margins become chlorotic, wilted and blighted. Reddish-orange perithecia appear at and just above soil line from mid-June through the end of the season. Ascospores may be exuded from perithecia in a visible thick, yellow liquid.

On soybean: Leaves become chlorotic, browning between veins, with early defoliation and simultaneous petiole drop. Roots show similar black rot symptoms. Reddish-orange perithecia appear at and just above soil line. Soybean is usually more tolerant than peanut. Symptoms often appear late in the season, after pod set, and yields are not always adversely affected.

Northern root-knot nematode Meloidogyne hapla and the ring nematode Criconemella ornata exacerbate CBR. Disease severity may increase if roots are injured by preplant herbicides. Disease development is also more likely in soils high in organic matter or otherwise more likely to retain moisture (Phipps and Beute, 1997).

Ecology and life cycle:

The fungus overwinters as microsclerotia. Intercellular penetration of the root cortex and Rhizobium nodules occurs within 24 hours of germination, and hyphae begin producing microsclerotia within several days. Peanut can produce protective periderms (dermal tissues typical of secondary growth) to wall off invaded and injured areas, and differences between susceptible and resistant varieties of peanut may be mainly due to the speed with which these periderms can be produced. Epidermal weaknesses may occur as a result of injury or the emergence of secondary roots, providing the pathogen additional entrance points.

The decay of dead tissue releases microsclerotia into the soil. Microsclerotia can be dispersed in wind-blown plant debris and by equipment. These propagules are not effective saprophytic competitors.

Perithecial initials can be found on peanut stems within a week after inoculation, and perithecia will form in large quantities on stems if adequate moisture is available. In North Carolina, perithecia have been observed as early as mid-June. Mature ascospores can be present within two to three weeks after inoculation. Conidia are rarely observed under field conditions, but ascospores appear to play a significant role in secondary disease spread within a growing season. Ascospores are discharged both by ejection and in viscous droplets that presumably can be dispersed by rain splash and runoff. Ascospore formation and discharge appear to be controlled by day-night relative humidity fluctuations. Ascospores mature under 100% night-time humidity conditions. The drop in humidity that occurs at dawn triggers a widespread ascospore discharge coinciding with dew precipitation. Both ascospores and conidia are extremely sensitive to desiccation, and survival of either under normal day-time field levels of temperature and humidity is under 10% after two minutes. Ascospore ejection occurs between 20 - 30 ° C, and maximally at 25 ° C, more or less coinciding with vegetative growth temperature optima (Rowe and Beute, 1974).

Management

Peanut seed coat testae and cotyledons are also colonized. Infected seed have discolored or "flecked" testae (Porter et al., 1991). The potential role of seed transmission of the disease was probably overlooked until recently, since almost all dark seed are removed during normal sorting and screening. Application of protectant fungicides to seeds are effective in disease control.

The disease slows over 25 ° C and ceases at 35 ° C. Delaying planting to take advantage of this factor has been successful at reducing disease, but few yield increases have been realized due to the offsetting effects of later harvests.

C. parasiticum is a tropical and subtropical pathogen, and disease severity is sensitive to winter temperatures, particularly in Virginia where it is at the northern end of its range. Delaying tillage till spring keeps propagules away from insulating deep soil, and sometimes can reduce disease.

Applications of nitrogen to peanut fields also can reduce severity of CBR, presumably because fertilization reduces formation of Rhizobium nodules, thus providing fewer infection courts. Fertilization of peanut, however, may result in lower yields due to delayed flowering.

Links to other sites:

USDA ARS Systemic Botany and Mycology
NC State University, Cooperative Extension Service,    Soybean Stem and Root Rots
National IPM Network  (symptoms of Cylindrocladium black rot )
NC State University,  Cooperative Extension Service, Peanut Disease Control:  CBR Management 

Key references:



Return to Pathogen Profiles


Posted: May, 1999


 
 
 
 
 
 

Peanut field

Peanut field showing plants dying from Cylindrocladium black rot (CBR). 
Courtesy Jack Bailey 
 

perithecia
Perithecium. 
Reprinted with permission of The American Phytopathological Society 
 


asci
Asci. 
Reprinted with permission of The American Phytopathological Society 
 

Microsclerotia
Microsclerotia. 
Reprinted with permission of The American Phytopathological Society 
 

Conidia

Conidia. 
Reprinted with permission of The American Phytopathological Society 
 

vesicles
Vesicles. 
Reprinted with permission of The American Phytopathological Society 
 

Conidiaphore
Conidiophore-bearing stipes. Reprinted with permission of The American Phytopathological Society 
 


 
 
 
 
 
 
 

Lesions

Peanut roots and pods which have been rotted by Cylindrocladium black rot (CBR). 
Courtesy Jack Bailey 
 


 
 
 
 

Red perithecium

Perithecia on peanut root. 
Courtesy Jack Bailey.


 
 

Soybean stems

Soybean stem showing the red perithecia of the Cylindrocladium fungus. 
Courtesy S. Koenning. 
 


 

Leaves

Foliar symptoms associated with red crown rot of soybean. 
Courtesy S. Koenning. 
 

Debris

Microsclerotia in wind-blown debris. 
Reprinted by permission of the American Phytopathological Society 
 

Peanut seeds

Healthy (top row) vs. "speckled" peanut seed. Speckles are microsclerotia of the Cylindrocladium fungus. Courtesy Jack Bailey