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:
Bell, D. K. and E. K. Sobers. 1966. A peg, pod, and root necrosis of
peanuts caused by a species of Calonectria. Phytopath.56(11):1361-1364.
Brenneman, T.B., G.B. Padgett, and R.G. McDaniel. 1998.First report
of Cylindrocladium black rot (C. Parasiticum) on partridgepea
and sicklepod. Pl. Dis. 82(9):1064.
Crous, P. W., M J. Wingfield, and A. C. Alfenas. 1993. Cylindrocladium
parasiticum sp. nov., a new name for C. crotalariae. Mycol.
Res. 97(7): 889-896.
Griffin, G. J., D. A. Roth and N. L. Powell. 1978. Physical factors
that influence the recover of microsclerotia populations of Cylindrocladium
crotalariae from naturally infested soils. Phytopath. 68(6): 887-891.
Hwang, S. C. and W. H. Ko. 1976. Biology of condia, ascospores and microsclerotia
of Calonectria crotalariae in soil. Phytopath. 66(1):51-54.
Padgett, G.B., T.B. Brenneman, and N.E. El-Gholl. 1995.First report
of Cylindrocladium black rot (C. parasiticum) on Florida
beggarweed. Pl. Dis. 79(5):539.
Phipps, P. M. and M.K. Beute. 1997. Cylindrocladium black rot..
In: Compendium of Peanut Diseases. 2nd Ed. Amer. Phytopathological
Society. St. Paul, Mn.
Phipps, P. M., M. K. Beute and K. R. Berker. 1976. An elutriation method
for quantitative isolation of Cylindrocladium crotalariae microsclerotia
from peanut field soil. Phytopath. 66(10):1255-1259.
Porter, D. M., F. S. Wright, R. A. Taber and D. H. Smith. 1991. Colonization
of peanut seed by Cylindrocladium crotalariae. Phytopathology 81(8):
896-900.
Rowe, R. C., and M. K. Beute. 1975. Ascospore formation and discharge
by Calonectria crotalariae. Phytopath. 65(4):393-398.
Sidebottom, J. R. and M. K. Beute. 1989. Inducing soil suppression to
Cylindrocladium Black Rot of peanut through crop rotations with
soybean. Plant Dis. 73(8):679-685.
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Posted: May, 1999
