August 19, 2005
From: ProMED-mail <promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of Botrytis blight of peanut caused by Botrytis cinerea in Georgia
J. E. Woodward, T. B. Brenneman, R. C. Kemerait, Jr., and A. K. Culbreath, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793; and J. R. Clark, University of Georgia Cooperative Extension Service, Baxley 31513. Plant Dis. 89:910, 2005; published on-line as DOI: 10.1094/PD-89-0910C. Accepted for publication 10 May 2005.

Because of the importance of spotted wilt caused by Tomato spotted wilt virus (TSWV), most peanut (_Arachis hypogaea_ L.) breeding programs in the southeastern United States are focusing on developing resistance to TSWV. Many of the cultivars with improved resistance to TSWV are late maturing, requiring 150 days to reach optimum maturity. This factor could greatly impact disease problems at harvest.

During November of 2004, an unknown disease was observed on peanut cvs. Georgia 02-C and Hull in a commercial field in Appling County. Symptoms included wilting stems with water-soaked lesions and a dense, gray mold growing on infected tissues. Final disease incidence was less than 5 percent. For isolation, diseased tissue was surface-sterilized by soaking in 0.5 percent sodium hypochlorite for 1 min, air dried, plated on potato
dextrose agar (PDA), and incubated at 20C. _Botrytis cinerea_ Pers.:Fr., causal agent of Botrytis blight, was isolated from the margins of infected tissue.

Mycelia were initially white but became gray after 72 h, at which time tall, branched, septate conidiophores formed. Mature, unicellular, ellipsoid, hyaline conidia (8.9 x 10.4 micrometers) formed in botryose heads (1). Hard, black, irregular-shaped sclerotia formed after 2 weeks.

Stems of greenhouse-grown peanut plants (cv. Georgia Green) were inoculated with PDA plugs colonized with either _B. cinerea_ or _B. allii_ Munn. Inoculations were made 3 cm below the last fully expanded leaf on wounded
and nonwounded tissue. Noncolonized PDA plugs served as controls (n = 9). Plants were arranged in a dew chamber at 20C in a randomized complete block design.

Lesions and spore masses identical to those observed in the field appeared 3 to 5 days after being inoculated with _B. cinerea_. The _B. allii_ inoculations caused only superficial lesions. After 5 days, mean lesion lengths for _B. cinerea_ were 59 and 37 mm for wounded and nonwounded inoculations, respectively. _B. cinerea_ was recovered from 100 percent of the symptomatic tissues. Botrytis blight is considered a late-season disease that occurs in cool, wet weather (3).

Symptoms similar to those of Botrytis blight were observed on mature and over-mature peanut in Georgia and have been cited as "unpublished observations" (2); however, to our knowledge, this is the 1st report of the disease in Georgia. Although Botrytis blight is not considered a major peanut disease, it may become more prevalent at harvest as producers utilize late-maturing cultivars to manage spotted wilt.

References:

(1) H. L. Barnett and B. B. Hunter. Illustrated Guide of Imperfect Fungi. 4th ed. The American Phytopathological Society, St. Paul, MN, 1998.

(2) K. H. Garren and C. Wilson. Peanut Diseases. Pages 262-333 in: The Peanut, the Unpredictable Legume. The National Fertilizer Assoc. Washington
D.C. 1951.

(3) D. M. Porter. Botrytis blight. Pages 10-11 in: Compendium of Peanut Diseases. 2nd ed. N. Kokalis-Burelle et al., eds. The American Phytopathological Society, St. Paul, MN. 1997.

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[Botrytis blight of peanut is a late-season disease that generally occurs in cool, wet weather. Infected tissues rapidly develop a water-soaked, brown appearance and are frequently covered by a greyish-brown mold. Although all currently planted varieties are susceptible to Botrytis blight, NC 17 appears to be highly susceptible to this disease. In the United States, Botrytis blight occurs predominantly in certain areas of West Texas. Symptoms of this disease closely resemble Sclerotinia blight. Disease management is best accomplished by harvesting in a timely fashion and avoiding plant injury so as to reduce symptom incidence and severity.

Links:
<http://plantpathology.tamu.edu/Texlab/Fiber/Peanuts/atlas-toc.html>
<http://ipm.ncsu.edu/Production_Guides/Peanuts/chapter%206.pdf>
- Mod.DH]