Disease Note.

A New Stem Canker of Peanut in Alabama Caused by Fusarium oxysporum: A Wound-Dependent Disease. J. M. Mullen, Department of Plant Pathology, Auburn University, Auburn, AL 36849. A. K. Hagan, Department of Plant Pathology, Auburn University, Auburn, AL 36849; and P. E. Nelson, Department of Plant Pathology, Pennsylvania State University, University Park 16802. Plant Dis. 80:1301. Accepted for publication 6 August 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1301A.

In August 1992, after several weeks of wet weather, a widespread stem canker was noted in two fields of peanut (Arachis hypogaea L.) cv. Florunner in Covington County, AL. Reddish to dark brown, sunken, elongate (0.5 to 3.0 cm), girdling lesions were located along the central stems at varying distances above the soil line. Foliage distal to the cankers showed chlorosis and wilt. Sporodochia of a Fusarium sp. were observed on the surface of some lesions, and F. oxysporum Schlechtend.:Fr. was consistently isolated from canker margins on acidified potato dextrose agar (aPDA). Pathogenicity of F. oxysporum was tested on two separate occasions on 9- and 13-week-old plants of peanut cv. Florunner. On both occasions, a total of 15 stems on five plants were inoculated with mycelial agar blocks that were held against each stem with a Parafilm wrap. The 9-week-old plants were not wounded; the 13-week-old plants were wounded by slicing the epidermis with a scalpel (a 3- to 4-mm-long slice) just prior to inoculation. With the 9-week-old plants, two noninoculated, nonwounded plants were included as controls. With the 13-week-old plants, two noninoculated, wounded plants were included as controls. Three weeks after inoculation, brown to black lesions (0.5 to 2.0 cm long) were present at each wound inoculation site. F. oxysporum was consistently isolated from canker margins. Cankers did not form on inoculated unwounded sites or uninoculated controls. The apparent association of wounds with canker development in greenhouse tests may indicate the need for mechanical or environmental injury to the central stems of peanut prior to infection by F. oxysporum. F. oxysporum has not previously been reported as causing a stem canker of peanut. A preliminary report of initial studies has been published (1).