A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

June 26, 2003
Source: Amer Phytopathol Soc, DISEASE NOTES [edited]

First Report of Plectosporium Blight on Pumpkin Caused by Plectosporium tabacinum in Alabama
J. M. Mullen and E. J. Sikora, Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849. Plant Dis. 87:749, 2003; published on-line as D-2003- 0416-01N, 2003. Accepted for publication 6 April 2003.

In October of 2001, _Plectosporium tabacinum_ [Pt] (van Beyma) M.E. Palm, W. Gams, & H.I. Nirenberg (formerly _Microdochium tabacinum_ (von Arx, 1984) and _Fusarium tabacinum_ (Gams & Gerlagh, 1968) was observed in field plantings of pumpkin (_Cucurbita pepo_ L.) in Cullman and Jackson counties in north Alabama.

Symptoms were white or tan, spindle-shaped lesions on stems and leafpetioles and slightly raised, corky, white or light brown lesions on pumpkin fruit and fruit stems. Pumpkin symptoms were identical to a
previous description of Pt (published as _M. tabacinum_) on pumpkin, zucchini, and yellow summer squash (1).

Disease severity ranged from less than 10 percent stem tissue damage on pumpkins in Cullman County to 40 to 45 percent stem tissue damage on pumpkins in Jackson County. A field section of pumpkins in Jackson County sprayed with the fungicides azoxystrobin (0.20 kg a.i./ha) and chlorothalonil (2.44 kg a.i./ha), alternated weekly beginning at vine-run, had stem damage of approximately 5 percent compared to ca. 45 percent stem damage on pumpkins in an unsprayed field section.

A 50 percent reduction in marketable fruit due to Pt was observed in the unsprayed field section compared to the section sprayed weekly with fungicides.

Thin slices of lesions, taken from stem and fruit surfaces and examined microscopically, showed 1- or 2-celled, hyaline, bilaterally symmetric spores, 7.0 to 8.5 × 2.8 to 3.0 micrometers. The ends of the spores were slightly narrowed and rounded. Spore characteristics were identical to previous descriptions of Pt produced in culture and on diseased pumpkins and squash (2,3).

Surface-sterilized tissue from fruit lesion margins was plated on PDA and incubated under light (Sylvania Gro-Lux, 40w) with a light/dark cycle of 12 h at 23°C. After 10 days, spores were observed that were similar to those from fruit except that they were multiguttulate and had a phialide arrangement. The fungal mycelium was pale pink to pale orange and closely appressed to the agar. Fungal characteristics in culture agree with a previous description of Pt in culture (2).

To our knowledge, this is the first report of Pt in Alabama.

References:

(1) S. C. Bost and C. A. Mullins. Plant Dis. 76:861, 1992.

(2) M. E. Palm et al. Mycologia 87(3):397, 1995; (3) T. A. Zitter. Microdochium blight. Page 28 in: Compendium of Cucurbit Diseases. T. A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. The American
Phytopathological Society, St. Paul, MN, 1996.

[Plectosporium blight primarily infects pumpkin, yellow squash and zucchini squash. Apparently there are no resistant cultivars and crop losses can exceed 50 percent. Disease management depends upon crop rotation with non-cucurbit crops and the use of chemical fungicides containing chlorothalonil or trifloxystrobin. -Mod.DH]