March 16, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of Plectosporium blight on pumpkin and squash caused by Plectosporium tabacinum in New York State
P. Jimenez and T. A. Zitter, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. 89:432, 2005; published on-line as DOI: 10.1094/PD-89-0432A. Accepted for publication 5 Jan 2005.

In early August 2004, pumpkin and zucchini squash (_Cucurbita pepo_) plants grown in conventional and organic commercial operations in Orange and Dutchess counties, respectively, showed spindle-shaped lesions on vegetative tissues and silver russeting and spots on fruit, typical of Plectosporium blight. Approximately 20 percent of pumpkin fruit were affected at this early time in yield development, while the zucchini planting had been abandoned due to disease.

Symptomatic pieces of stem, petioles, and main leaf veins were excised, surface disinfected with 0.5 percent sodium hypochlorite, placed on one-quarter-strength potato dextrose agar, and incubated at 21 deg C with a
12-h photoperiod. Pale pink colonies with pinkish, hyaline, aerial mycelium developed from the tissues. When examined microscopically, simple and branched conidiophores with apical phialides were observed, as well as non- and one-septate ellipsoidal to slightly curved conidia that measured 7.5 to 13.0 x 2.5 to 3.3 micrometers. The fungus fits the description of _Plectosporium tabacinum_ (van Beyma) M.E. Palm, W. Gams, & H.I. Nirenberg
(synonyms _Microdochium tabacinum_ (von Arx, 1984) and _Fusarium tabacinum_ (Gams & Gerlagh, 1968) (1).

Pathogenicity was tested on 10 seedlings each of pumpkin, zucchini, gourd (_C. pepo_), winter squash (_C. moschata_), and cucumber (_Cucumis sativa_). Plants were spray-inoculated at the 3 true-leaf stage with a spore suspension at 10 000 conidia/ml in water with 1 percent gelatin. Plants were held overnight in a moist chamber and then transplanted into 12-cm-diameter pots and kept in the greenhouse for the rest of the experiment. _P. tabacinum_ was reisolated from all inoculated plants which completes Koch's postulates.

Symptoms were noted 3 days after inoculation on pumpkin, zucchini, and gourd, with typical spindle-shaped lesions on the main stem, petioles, and main leaf veins (2). Symptoms developed after 1 week on winter squash, and lesions were mostly concentrated on the older portion of the stem with occasional lesions on the petiole and main leaf veins. Symptoms on cucumber, however, did not develop until 2 weeks after inoculation and appeared as an inconspicuous line of coalesced lesions on the ridges of the main stem only. These symptoms could easily be misidentified as physical abrasions from handling or from wind scarring. These results confirm the high susceptibility of _C. pepo_ species, and indicate that other cucurbits are susceptible, albeit at a lower level.

To our knowledge, this is the 1st report of _P. tabacinum_ in New York. A voucher specimen has been deposited in the Cornell Plant Pathology Herbarium (Accession No. CUP 67504).

References:
(1) M. E. Palm et al. Mycologia 87:397, 1995;
(2) 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.

--
ProMED-mail
<promed@promedmail.org>

[Plectosporium blight [Pb], caused by _Plectosporium tabacinum_, is a new destructive disease of cucurbits in New England. Pb was found in Tennessee in 1988 and has since spread rapidly throughout the eastern United States,
occurring on a farm in Massachusetts in 2000 and on at least a dozen farms in Connecticut and Massachusetts in 2003. In the fall of 2004, after 2 seasons of rainy weather, it was present in every field surveyed from Long Island Sound to Burlington, Vermont. Pb can cause significant damage to a wide variety of cucurbit crops in Europe and Asia, but the U.S. strain seems to primarily damage pumpkins, summer squash, zucchini and a few
varieties of gourds. In wet years, which favor disease development and spread, crop losses in no-spray and low-spray fields can range from 50 to 100 percent. Fortunately, this disease is easily recognized and can be effectively managed.

Recommended management strategies include a 3-year crop rotation, planting in sites with good air circulation to encourage rapid drying of the foliage,switching to trickle irrigation, scouting fields to confirm presence of Pb, applying fungicides, and plowing under crop residue after harvest. There are no known pumpkin or summer squash varieties, although differences in susceptibility do occur. Pumpkin varieties Sorcerer, Gold Standard and sugar pumpkins seem to be less susceptible than other varieties grown in the same fields.

Link: <http://www.hort.uconn.edu/ipm/veg/htms/plectosp.htm> -Mod.DH]