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2003 Plant Management Network.
Accepted for publication 15 April 2003. Published 12 May 2003.


First Report of Downy Mildew of Chives Caused by Peronospora destructor in the Pacific Northwest


Dean A. Glawe, Plant Pathologist, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup, WA 98371-4998


Corresponding author: Dean A. Glawe. glawe@wsu.edu


Glawe, D. A. 2003. First Report of downy mildew of chives caused by Peronospora destructor in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2003-0512-01-HN.


Chive (Allium schoenoprasum L.) is one of the specialty crops grown by farmers in the Puget Sound region of Washington State. In September, 2002, downy mildew symptoms were observed in a 0.2 hectare field planting of chive near Fall City, King County, WA. Downy mildew had not been reported previously on chive in the Pacific Northwest.

According to the grower, the planting consisted of two or three different intermixed, unidentified cultivars of chives. Fifty-six percent of 69 sampled plants exhibited symptoms of the disease (Figs. 1 and 2). The most common symptoms were chlorotic tips of affected leaves. As the disease progressed, entire leaves became tan-colored to light brown with regions of brownish to purple sporulation (Fig. 3). Identification of the causal agent, Peronospora destructor (Berk.) Casp. in Berk., was confirmed on the basis of microscopic features that included monopodially branched sporangiophores with acutely tapering termini (Fig. 3), and sporangia (Fig. 4) that were brownish, pyriiform to oblong, and measured 38 to 63 16 to 31 m (1,3). A voucher specimen was deposited in the Mycological Herbarium at Washington State University (WSP number 70309).


     
 

Fig. 1. Chive plant exhibiting symptoms of downy mildew, including chlorotic and necrotic leaves.

 

Fig. 2. Chive leaves exhibiting chlorosis and necrosis resulting from downy mildew.

 

     
 

Fig. 3. Sporangiophore of Peronospora destructor (by brightfield microscopy).

 

Fig. 4. Sporangium of Peronospora destructor (by differential interference microscopy).

 

There were no significant economic losses from this disease outbreak because the crop was grown for the early season market and the disease was not detectable at the time of harvest. Had the crop been grown for a late season market, the marketability of the crop would have been seriously affected by the detrimental effect of the disease on the appearance of leaves. The occurrence of P. destructor on chives in the Puget Sound region has broad implications. This disease could become more significant in the future under the humid weather and mild temperatures characteristic of climate in the Puget Sound area, and chives may serve as a source of inoculum for other regions (2,4). Chive plantings, even though small in land area, also could play a role in, and be affected by, the epidemiology of this disease on other Allium species in the region, including A. porrum L. and A. cepa L.


Literature Cited

1. Mukerji, K. G. 1975. Peronospora destructor. CMI Descr. Pathog. Fungi Bact. No. 456.

2. Pauti, J. 1989. Epidemiology, prediction and control of onion downy mildew caused by Peronospora destructor. Phytoparasitica 17:31-48.

3. Schwartz, H. F., and Mohan, S. K. 1995. Compendium of Onion and Garlic Diseases. American Phytopathological Society, St. Paul, MN.

4. Yarwood, C. E. 1943. Onion downy mildew. Hilgardia 14:595-691.