November 24, 2005
From: American Phytopathological Society, Plant Disease Notes, November 2005 [edited] <http://www.apsnet.org/pd/searchnotes/2005/PD-89-1245A.asp>

First report of Cylindrocladium black rot caused by Cylindrocladium parasiticum on peanut in Texas
T. A. Wheeler, Department of Plant Pathology and Microbiology, Texas A&M University, Lubbock 79403-9803; and M. C. Black, Department of Plant Pathology and Microbiology, Texas A&M University, Uvalde 78802-1849. Plant Dis. 89:1245, 2005; published on-line as DOI: 10.1094/PD-89-1245A. Accepted for publication 12 Jul 2005.

During August 2004, _Cylindrocladium parasiticum_ Crous, M.J. Wingf., & Alfenas (teleomorph _Calonectria ilicicola_ Boedijin & Reitsma) was isolated from peanut (_Arachis hypogaea_ L.) cv. NC 7 taken from an irrigated field in Terry County, TX. On 24 Sep 2004, the mean length of patches with symptoms of dead plants and confirmed for the presence of _C. parasiticum_ was 40 cm (averaged over 52 patches). Pods, pegs, roots, and lower stems of affected plants had decayed black lesions. No perithecia were observed.

Roots were plated on water agar, and mycelia growth was transferred to potato dextrose agar (PDA). Conidia and microsclerotia typical of _C. parasiticum_ had formed at 14 days. After 21 days on PDA, the following mean measurements were recorded: macroconidia 57 x 7 micrometers (usually 2 septations); stipe  115 x 4 micrometers; and sphaeropedunculate vesicle 15 x 10 micrometers. These are within reported ranges for _C. parasiticum_ (1).

4-week-old cultures were comminuted in tap water and added (mycelium and microsclerotia) to potting medium (noninfested nonsterile peanut field soil/peat moss potting mix, 1:1). Peanut-specific _Bradyrhizobium_ sp. was
applied before planting. 3-day-old peanut cv. Tamrun 88 seedlings (3 in number) were transplanted in infested soil (4 replicate pots, 5 isolates). Root, hypocotyl, pod, peg, and lower stem lesions were evident after 8 (Trial
1, one isolate) and 16 weeks (Trial 2, 4 isolates). Virulence varied among isolates (3). _C. parasiticum_ was reisolated on acidified PDA after both trials.

In Trial 3, 6 plant species (3 replicate pots, 5 plants per pot) were challenged with one isolate by drenching a tap water suspension of comminuted microsclerotia and mycelium from 4-week-old PDA cultures into potting medium
and transplanting peanut seedlings or planting seeds for other hosts. Root rot severity (0 to 5 index) (3) and reisolation percentages were cv. Tamrun 88 peanut 2.0, 100 percent; cv. Tamrun 96 peanut 2.0, 92 percent; cv. Hutcheson soybean (_Glycine max_ (L.) Merr.) 3.3, 64 percent; cv. Blue Lake 274 green bean (_Phaseolus vulgaris_ L.) 2.7, 40 percent; cv. California Blackeye 8046 southern pea (_Vigna unguiculata_ (L.) Walp. 2.0, 70 percent; and cv. Jubilee Hybrid sweet corn (Zea mays L.) 0.0, 100 percent.

Noninoculated peanut controls in all trials had no black decayed root lesions and attempts to isolate the fungus were unsuccessful. Peanut seeds planted in the production field were obtained from the southeastern United States. This field had been scheduled for seed production until _C. parasiticum_ was identified. Temperatures and rainfall amounts during the 2004 growing season were less and greater than long-term averages, respectively. No other infested peanut fields have been confirmed or suspected in the region or state.

There is continued risk of contamination from shipments of infected seeds from infested areas (2). This pathogen may pose a serious threat to over 100 000 ha of peanut production in western Texas and eastern New Mexico.

References:
(1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul, MN, 2002.
(2) B. L. Randall-Schadel et al. Plant Dis. 85:362, 2001.
(3) R. C. Rowe and M. K. Beute. Phytopathology 65:422, 1975.

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[Cylindrocladium black rot (CBR) was first found in 1965 in peanut in southwest Georgia and subsequently spread to Florida, in Alachua and Columbia counties. In the mid 1980s CBR was found in peanut in the panhandle section of Florida. Since 1975, CBR has been found in alfalfa, clovers, and soybean. Other crops reported to be susceptible to CBR are cowpea, bean and blueberry.

Yield losses from CBR in some infested peanut fields in Florida have exceeded 50 percent. CBR has become a limiting factor for production of peanut in some fields in the panhandle area, particularly in Santa Rosa County. In general, CBR appears to be gradually increasing in severity in peanut throughout the peanut-producing areas of Florida.

Management of CBR includes avoidance of susceptible crops, a crop rotation of 4-5 years, elimination or reduction of weeds such as hairy indigo (_Indigofera hirsuta_ ), beggarweed (_Desmodium purpureum_ ) and coffeeweed (_Sesbania exaltata_). Soils should be well drained. Phytosanitary measures such as removal of soil and plant debris from tractor tires and implements before moving them to non-infested fields is advised. Some peanut cultivars possess low levels of resistance to CBR.

Chemical control for CBR in peanut has provided some control. In Virginia, North Carolina, and to a limited extent in Georgia, preplant fumigation with metam-sodium has been used successfully, particularly if fumigation is coupled with use of a resistant variety. In Florida, CBR has been suppressed in peanut by means of post-plant sprays of approved fungicides at mid-season.

Links:
<http://plantpath.ifas.ufl.edu/takextpub/FactSheets/pp0139.pdf>
<http://nespal.cpes.peachnet.edu/pa/home/main.asp?TargetDir=9&content=8&media=>
<http://www.cals.ncsu.edu/course/pp728/Cylindrocladium/parasit.htm>
- Mod.DH]