© 2005 Plant Management Network.
First Report of Powdery Mildew of Carrot and Parsley Caused by Erysiphe heraclei in Washington State
Dean A. Glawe, Plant Pathologist, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998; Gary Q. Pelter, Washington State University Extension, County Courthouse, P.O. Box 37, Ephrata 98823; and Lindsey J. du Toit, Assistant/Extension Plant Pathologist, Northwest Washington Research and Extension Center, Washington State University, 16650 State Route 536, Mount Vernon 98273-4768
Corresponding author: Dean A. Glawe. email@example.com
Glawe, D. A., Pelter, G. Q., and du Toit, L. J. 2005. First report of powdery mildew of carrot and parsley caused by Erysiphe heraclei in Washington State. Online. Plant Health Progress doi:10.1094/PHP-2005-0114-01-HN.
Since 1982 (G. Q. Pelter, personal communication), powdery mildew has been observed on carrot [Daucus carota L. subsp. sativus (Hoffm.) Arcang.] processing crops, and on carrot and parsley [Petroselinum crispum (Mill.) Nym.: A. W. Hill] seed crops in Washington, but no published report of this disease in Washington exists. From 2002 to 2004, the anamorph of Erysiphe heraclei DC was observed on plants from processing carrot fields in central Washington. The teleomorph of E. heraclei, not previously reported in Washington, was discovered in a processing carrot field in Grant County in September 2004. A fungus matching the description of the anamorph of E. heraclei (2,3) also was found attacking parsley in a home garden in Grant County. This report documents the occurrence of E. heraclei and its teleomorph on carrot in Washington and the occurrence of E. heraclei on parsley in Washington.
Disease symptoms and signs included chlorotic and necrotic areas on affected leaves with conspicuous white to gray masses of conidia and mycelia. Severity of powdery mildew ranged from < 10 to > 50% of the foliage affected in individual crops. Preliminary observations suggest incidence and severity may be affected by cultivar and type of irrigation system under which the crop is grown (the disease appeared to be more severe in furrow- than overhead-irrigated crops).
The fungus formed the following anamorphic features on both hosts: hyphae
were ectophytic with lobed appressoria; conidiophores bore single conidia (Fig.
1); conidiophore foot cells were cylindrical,
straight, and measured (L × W) (22.5-) 26.5-39.5 (-40.0) × (8.0-) 8.5-10.0 (-10.5)
µm; conidia (Fig. 2) were short-cylindrical to cylindrical, lacked fibrosin
bodies, and measured (29.5-) 32.0-43.5 (-47.0) × (10.5-) 12.5-16.5 (-19.0) µm. The
teleomorph, observed on carrot leaves, included subspherical ascocarps (Fig. 3) that
became dark brown to black, formed hyphoid appendages, and measured
(107-) 112-153 (-170) µm in diameter. Ascocarps each contained multiple asci (Fig.
4) that were saccate, short-stipitate, measured (52.5-) 57.5-70.5 (-78.5) ×
(44.0-) 46.0-60.0 (-64.5) µm, and each contained 3 to 5 ascospores. Ascospores
were subhyaline, ovoid to ellipsoid, multiguttulate, and measured
19.0-26.5 (-27.5) ×
This fungus fits Braun’s (3) concept of E. heraclei, the only Erysiphe species he listed on the Apiaceae. The names Erysiphe polygoni DC and E. umbelliferarum (Lév.) de Bary also have been used for similar fungi attacking Apiaceae (2) but reflect superceded taxonomic concepts (2,3). Erysiphe heraclei has been reported on various species of Apiaceae in other regions in North America (1,4). Powdery mildew also has been observed on carrot in Oregon (J. W. Pscheidt, personal communication). This appears to be the second report of E. heraclei on parsley in North America, a host reported previously in California (4).
Contamination of seed lots with ascocarps of E. heraclei has been suggested as a possible means of disseminating the pathogen, although transmission by seeds has not been demonstrated (1,3). Because the Pacific Northwest provides up to 75% of the U.S. supply of carrot seed, the discovery of the teleomorph in central Washington suggests that additional research is needed to investigate the risk of disseminating the pathogen with carrot seed.
Erysiphe heraclei includes many host-specific races (2,3). Additional research on host ranges of Washington strains, supported by molecular data, is needed to determine the level of biologic and pathogenic diversity within the species; the risks the fungus poses to processing, fresh market, and seed crops; and the role of alternative hosts in the epidemiology of this disease.
1. Abercrombie, K., and Finch, H. C. 1976. Powdery mildew of carrot in California. Plant Dis. Rep. 60:781-782.
2. Aegerter, B. J. 2002. Powdery mildew. Pages 22-23 in: Compendium of Umbelliferous Crop Diseases. R. M. Davis and R. N. Raid, eds. American Phytopathological Society, St. Paul, MN.
3. Braun, U. 1987. A monograph of the Erysiphales (powdery mildews). Beih. Nova Hedwigia 89:1-700.
4. Koike, S. T., and Saenz, G. S. 1994. Occurrence of powdery mildew on parsley in California. Plant Dis. 78:1219.